how to write references at the end of a research paper

How to Cite in APA Style (7th Edition)

• About APA 7th ed.
• In-text Citations

Basic Rules

Dois and urls.

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• Sample Reference List
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Reference List format

Start of References Page (Section 2.12)

• Start the reference list on a new page after the text and before any tables, figures, and/or appendices.
• The word References  should appear in uppercase and lowercase letters, in bold, and centered; do not underline, or put the word "References" in quotation marks.
• See the Sample Reference List on this library guide.

Spacing (Section 2.12)

• Double-space all reference entries (including between and within references), and put them in a hanging indent format, i.e. all lines after the first line of each reference entry should be indented 0.5 inch from the left margin.

References go A-Z by author's surname (Section 9.44)

• Arrange reference entries in alphabetical order by the surname of the first author followed by initials of the author's given name.

4 Key elements of reference entries

Author. date.   title. source..

          Who  |  When  |  What  |  Where

Nettle, D. (2005).   Happiness: The science behind your smile. Oxford University Press.

Diliello, T. C., Houghton, J. D., & Dawley, D. (2011). Narrowing the creativity gap: The moderating effects of perceived support for creativity. Journal of Psychology, 145 (3), 151-172. https://doi.org/10.1080/00223980.2010.548412

See this APA Style page for more details: Elements of Reference List Entries.

Missing information (No author, no date, etc.)

• Check out this APA Style page: Missing Reference Information .
• 1, 2-20 or 21+ authors
• One author with multiple publications
• Different authors with same surname
• 1 author:  Invert the authors' name if needed, give  surnames first , followed by a comma, and then add the initials. 

William SHAKESPEARE → Shakespeare, W.

CHAN Tai Man → Chan, T. M.

• 2 to 20 authors : Use a comma to separate the author's initials from the next author's name. Add an ampersand ( & ) before the final author.

Chan, T. M ., Cheung, B. B ., & Fung, C. C.

• 21 or more authors : Include the first 19 authors' names, then insert an ellipses (but no ampersand), and add the last author's name.

Chan, T. M., Cheung, B. B., Chung, C. C., Ding, D. D., Fung, E. E., Fung, F. F., Fung, G.G., Fung, H. H., Fung, I. I., Hung, J.J., Hung, K. K., Hung, L. L., Hung, M. M., Ip, N. N., Ip, O. O., Ip, P. P., Ip, Q. Q., Ip. R. R., Jiang, S. S., . . . Zhang, Y. Y.

More details: How many names to include in an APA Style reference ,  Section 9.8

• For several works by the same author or authors in the same order, arrange the reference entries by year of publication, the earliest first.

Chan, T. M. ( 2015 ).

Chan, T. M. ( 2017a ).

Chan, T. M. ( 2017b ).

More details: Section 9.46

• For several works by different first authors with the same surname, arrange the reference entries by different authors with the same surname and different initials alphabetically by first initial(s). 

Chan, K. L. (2015).

Chan, T. K. (2013).

More details: Section 9.48

Publication Date

• Enclose the date of publication in parentheses, followed by a period.

Chan, T. M. (2022).

• For a work that includes the month, day, and/or season along with the year, put the year first, followed by a comma, and then the month and date or season.

Chan, T. M. (2022, January 1).

Chan, T. M. (2022, Spring).

• If no date is available, write n.d. in parentheses  (Section 9.17) .

Chan, T. M. (n.d.).

More details: Section 9.14

Retrieval Date

Provide a retrieval date in the reference when citing an unstable work that is likely or meant to change over time (dictionary entry, Facebook page, etc.). Use this format to include a retrieval date: Retrieved October 10, 2022, from https://xxxxx

More details: Section 9.16 , Elements of Reference List Entries - Retrieval dates

DOI (digital object identifier)  is a unique identifier to help you locate a scholarly work (such as journal article, book chapter) online. 

A sample DOI link: https://doi.org/10.1080/00223980.2010.548412

• Include a DOI in the reference entry when it is available, regardless of whether you used the online version or the print version.
• For works without DOIs, include the URLs instead, if available. More details:  DOIs and URLs
• For works from academic research databases, do not include database information in the reference. Instead, the reference should be the same as the reference for a print version of the work. More details:  Database Information in Reference
• When a DOI or URL is too long, you may use shortened DOI or URL if desired.

More details: Sections 9.34 - 9.36

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APA Formatting and Style Guide (7th Edition)

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In-Text Citations

Resources on using in-text citations in APA style

Reference List

Resources on writing an APA style reference list, including citation formats

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APA Format for End References

APA format is the official style used by the   American Psychological Association .

APA style is used primarily in the social sciences and communicates data in a concise style that precisely describes material, makes the relationship between ideas or data as clear as possible, is generally in the active voice, and utilizes the past tense. In addition to being scientific and precise, you must use bias-free and inclusive language when writing in APA style. Your role is to be objective, to be conscious of word choice, and to avoid discriminatory language.

The font should remain the same throughout the paper. Options include 11-point sans-serif fonts, such as Calibri or Arial, and 12-point serif fonts, such as Times New Roman. Ultimately, check with your instructors about their font preferences. All text, including block quotes and the references section, should be double spaced.

Title pages include the paper title (in bold) followed by an extra space, the author (your name), affiliation (department and college), course number and name, instructor, and due date.

Crediting Sources

In-text citations.

In-text citations are included in the body of the paper. They identify the source by the author and its date of publication. Citations always correspond with an entry in the references section at the end of the paper. The two types of in-text citations,  narrative  and  parenthetical,  are shown below in the  paraphrase  and  direct   quotation  examples.

Paraphrasing means summarizing relevant information from a source. This method of borrowing is more commonly used in APA papers than quotations because it allows a writer to maintain their objective voice and combine the source’s ideas with their own. Paraphrases are always cited both in the text of the paper and in the reference page.

Paraphrase example using the narrative citation method

Rogers (1994) compared younger and older adults’ perceptions of economic stress.

Paraphrase example using the parenthetical citation method

The citation information is included at the end of the paraphrase in parenthesis.

In some instances, the hierarchical level at which employees worked significantly impacted their behavior in work groups (Mellers, Ortiz, & Smoot, 2006).

Direct quotations

Direct quotations are limited in APA style papers. Instead, you should paraphrase whenever possible to blend borrowed information with your context and voice. The   APA Publication Manual, 7 th   Edition   notes that a writer should use direct quotations “when reproducing an exact definition, when an author has said something memorably or succinctly, or when you want to respond to exact wording.” The author, years, and page number (or section identifier) is always paired with quoted material through the narrative or parenthetical citation format.

Short quotation example

This example uses the parenthetical in-text citation format.

In several double-blind experiments, "'the placebo effect' . . . disappeared when behaviors were studied in this manner" (Miele, 1993, p. 276).

Reference(s)

McCauley, S. M., & Christiansen, M. H. (2019). Language learning as language use: A cross-linguistic model of child language development.   Psychological Review, 126 (1),   1-51. http://doi.org/10.1037/rev0000126

Parenthetical citation:   (McCauley & Christiansen, 2019)

Narrative citation:   McCauley and Christiansen (2019)

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A Quick Guide to Referencing | Cite Your Sources Correctly

Referencing means acknowledging the sources you have used in your writing. Including references helps you support your claims and ensures that you avoid plagiarism .

There are many referencing styles, but they usually consist of two things:

• A citation wherever you refer to a source in your text.
• A reference list or bibliography at the end listing full details of all your sources.

The most common method of referencing in UK universities is Harvard style , which uses author-date citations in the text. Our free Harvard Reference Generator automatically creates accurate references in this style.

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Table of contents

Referencing styles, citing your sources with in-text citations, creating your reference list or bibliography, harvard referencing examples, frequently asked questions about referencing.

Each referencing style has different rules for presenting source information. For in-text citations, some use footnotes or endnotes , while others include the author’s surname and date of publication in brackets in the text.

The reference list or bibliography is presented differently in each style, with different rules for things like capitalisation, italics, and quotation marks in references.

Your university will usually tell you which referencing style to use; they may even have their own unique style. Always follow your university’s guidelines, and ask your tutor if you are unsure. The most common styles are summarised below.

Harvard referencing, the most commonly used style at UK universities, uses author–date in-text citations corresponding to an alphabetical bibliography or reference list at the end.

Harvard Referencing Guide

Vancouver referencing, used in biomedicine and other sciences, uses reference numbers in the text corresponding to a numbered reference list at the end.

Vancouver Referencing Guide

APA referencing, used in the social and behavioural sciences, uses author–date in-text citations corresponding to an alphabetical reference list at the end.

APA Referencing Guide APA Reference Generator

MHRA referencing, used in the humanities, uses footnotes in the text with source information, in addition to an alphabetised bibliography at the end.

MHRA Referencing Guide

OSCOLA referencing, used in law, uses footnotes in the text with source information, and an alphabetical bibliography at the end in longer texts.

OSCOLA Referencing Guide

Prevent plagiarism, run a free check.

In-text citations should be used whenever you quote, paraphrase, or refer to information from a source (e.g. a book, article, image, website, or video).

Quoting and paraphrasing

Quoting is when you directly copy some text from a source and enclose it in quotation marks to indicate that it is not your own writing.

Paraphrasing is when you rephrase the original source into your own words. In this case, you don’t use quotation marks, but you still need to include a citation.

In most referencing styles, page numbers are included when you’re quoting or paraphrasing a particular passage. If you are referring to the text as a whole, no page number is needed.

In-text citations

In-text citations are quick references to your sources. In Harvard referencing, you use the author’s surname and the date of publication in brackets.

Up to three authors are included in a Harvard in-text citation. If the source has more than three authors, include the first author followed by ‘ et al. ‘

The point of these citations is to direct your reader to the alphabetised reference list, where you give full information about each source. For example, to find the source cited above, the reader would look under ‘J’ in your reference list to find the title and publication details of the source.

Placement of in-text citations

In-text citations should be placed directly after the quotation or information they refer to, usually before a comma or full stop. If a sentence is supported by multiple sources, you can combine them in one set of brackets, separated by a semicolon.

If you mention the author’s name in the text already, you don’t include it in the citation, and you can place the citation immediately after the name.

• Another researcher warns that the results of this method are ‘inconsistent’ (Singh, 2018, p. 13) .
• Previous research has frequently illustrated the pitfalls of this method (Singh, 2018; Jones, 2016) .
• Singh (2018, p. 13) warns that the results of this method are ‘inconsistent’.

The terms ‘bibliography’ and ‘reference list’ are sometimes used interchangeably. Both refer to a list that contains full information on all the sources cited in your text. Sometimes ‘bibliography’ is used to mean a more extensive list, also containing sources that you consulted but did not cite in the text.

A reference list or bibliography is usually mandatory, since in-text citations typically don’t provide full source information. For styles that already include full source information in footnotes (e.g. OSCOLA and Chicago Style ), the bibliography is optional, although your university may still require you to include one.

Format of the reference list

Reference lists are usually alphabetised by authors’ last names. Each entry in the list appears on a new line, and a hanging indent is applied if an entry extends onto multiple lines.

Different source information is included for different source types. Each style provides detailed guidelines for exactly what information should be included and how it should be presented.

Below are some examples of reference list entries for common source types in Harvard style.

• Chapter of a book
• Journal article

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Your university should tell you which referencing style to follow. If you’re unsure, check with a supervisor. Commonly used styles include:

• Harvard referencing , the most commonly used style in UK universities.
• MHRA , used in humanities subjects.
• APA , used in the social sciences.
• Vancouver , used in biomedicine.
• OSCOLA , used in law.

Your university may have its own referencing style guide.

If you are allowed to choose which style to follow, we recommend Harvard referencing, as it is a straightforward and widely used style.

References should be included in your text whenever you use words, ideas, or information from a source. A source can be anything from a book or journal article to a website or YouTube video.

If you don’t acknowledge your sources, you can get in trouble for plagiarism .

To avoid plagiarism , always include a reference when you use words, ideas or information from a source. This shows that you are not trying to pass the work of others off as your own.

You must also properly quote or paraphrase the source. If you’re not sure whether you’ve done this correctly, you can use the Scribbr Plagiarism Checker to find and correct any mistakes.

Harvard referencing uses an author–date system. Sources are cited by the author’s last name and the publication year in brackets. Each Harvard in-text citation corresponds to an entry in the alphabetised reference list at the end of the paper.

Vancouver referencing uses a numerical system. Sources are cited by a number in parentheses or superscript. Each number corresponds to a full reference at the end of the paper.

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How to Cite: During and After

Two techniques of citing and documenting sources that are usually required in academic writing are:

• Providing a list of citations at the end of the paper
• Citing within the text of the paper

These two techniques are used together.

Cite At the End

Cite as you write.

Need more? See Resources for UCLA Students.

Plagiarism Isn't Just About Words

Did you know that according to the UCLA Dean of Students, using someone else's data in a computer exercise without authorization is considered plagiarism? It's true. Using someone's statistical data, computer code, or any other type of intellectual property without attributing the source is considered plagiarism. See the Office of the Dean of Students web site for more.

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Reference List: Common Reference List Examples

Article (with doi).

Alvarez, E., & Tippins, S. (2019). Socialization agents that Puerto Rican college students use to make financial decisions. Journal of Social Change , 11 (1), 75–85. https://doi.org/10.5590/JOSC.2019.11.1.07

Laplante, J. P., & Nolin, C. (2014). Consultas and socially responsible investing in Guatemala: A case study examining Maya perspectives on the Indigenous right to free, prior, and informed consent. Society & Natural Resources , 27 , 231–248. https://doi.org/10.1080/08941920.2013.861554

Use the DOI number for the source whenever one is available. DOI stands for "digital object identifier," a number specific to the article that can help others locate the source. In APA 7, format the DOI as a web address. Active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list. Also see our Quick Answer FAQ, "Can I use the DOI format provided by library databases?"

Jerrentrup, A., Mueller, T., Glowalla, U., Herder, M., Henrichs, N., Neubauer, A., & Schaefer, J. R. (2018). Teaching medicine with the help of “Dr. House.” PLoS ONE , 13 (3), Article e0193972. https://doi.org/10.1371/journal.pone.0193972

For journal articles that are assigned article numbers rather than page ranges, include the article number in place of the page range.

For more on citing electronic resources, see  Electronic Sources References .

Article (Without DOI)

Found in a common academic research database or in print.

Casler , T. (2020). Improving the graduate nursing experience through support on a social media platform. MEDSURG Nursing , 29 (2), 83–87.

If an article does not have a DOI and you retrieved it from a common academic research database through the university library, there is no need to include any additional electronic retrieval information. The reference list entry looks like the entry for a print copy of the article. (This format differs from APA 6 guidelines that recommended including the URL of a journal's homepage when the DOI was not available.) Note that APA 7 has additional guidance on reference list entries for articles found only in specific databases or archives such as Cochrane Database of Systematic Reviews, UpToDate, ProQuest Dissertations and Theses Global, and university archives. See APA 7, Section 9.30 for more information.

Found on an Open Access Website

Eaton, T. V., & Akers, M. D. (2007). Whistleblowing and good governance. CPA Journal , 77 (6), 66–71. http://archives.cpajournal.com/2007/607/essentials/p58.htm

Provide the direct web address/URL to a journal article found on the open web, often on an open access journal's website. In APA 7, active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list.

Weinstein, J. A. (2010).  Social change  (3rd ed.). Rowman & Littlefield.

If the book has an edition number, include it in parentheses after the title of the book. If the book does not list any edition information, do not include an edition number. The edition number is not italicized.

American Nurses Association. (2015). Nursing: Scope and standards of practice (3rd ed.).

If the author and publisher are the same, only include the author in its regular place and omit the publisher.

Lencioni, P. (2012). The advantage: Why organizational health trumps everything else in business . Jossey-Bass. https://amzn.to/343XPSJ

As a change from APA 6 to APA 7, it is no longer necessary to include the ebook format in the title. However, if you listened to an audiobook and the content differs from the text version (e.g., abridged content) or your discussion highlights elements of the audiobook (e.g., narrator's performance), then note that it is an audiobook in the title element in brackets. For ebooks and online audiobooks, also include the DOI number (if available) or nondatabase URL but leave out the electronic retrieval element if the ebook was found in a common academic research database, as with journal articles. APA 7 allows for the shortening of long DOIs and URLs, as shown in this example. See APA 7, Section 9.36 for more information.

Chapter in an Edited Book

Poe, M. (2017). Reframing race in teaching writing across the curriculum. In F. Condon & V. A. Young (Eds.), Performing antiracist pedagogy in rhetoric, writing, and communication (pp. 87–105). University Press of Colorado.

Include the page numbers of the chapter in parentheses after the book title.

Christensen, L. (2001). For my people: Celebrating community through poetry. In B. Bigelow, B. Harvey, S. Karp, & L. Miller (Eds.), Rethinking our classrooms: Teaching for equity and justice (Vol. 2, pp. 16–17). Rethinking Schools.

Also include the volume number or edition number in the parenthetical information after the book title when relevant.

Freud, S. (1961). The ego and the id. In J. Strachey (Ed.),  The standard edition of the complete psychological works of Sigmund Freud  (Vol. 19, pp. 3-66). Hogarth Press. (Original work published 1923)

When a text has been republished as part of an anthology collection, after the author’s name include the date of the version that was read. At the end of the entry, place the date of the original publication inside parenthesis along with the note “original work published.” For in-text citations of republished work, use both dates in the parenthetical citation, original date first with a slash separating the years, as in this example: Freud (1923/1961). For more information on reprinted or republished works, see APA 7, Sections 9.40-9.41.

Classroom Resources

Citing classroom resources.

If you need to cite content found in your online classroom, use the author (if there is one listed), the year of publication (if available), the title of the document, and the main URL of Walden classrooms. For example, you are citing study notes titled "Health Effects of Exposure to Forest Fires," but you do not know the author's name, your reference entry will look like this:

Health effects of exposure to forest fires [Lecture notes]. (2005). Walden University Canvas. https://waldenu.instructure.com

If you do know the author of the document, your reference will look like this:

Smith, A. (2005). Health effects of exposure to forest fires [PowerPoint slides]. Walden University Canvas. https://waldenu.instructure.com  

A few notes on citing course materials:

• [Lecture notes]
• [Course handout]
• [Study notes]
• It can be difficult to determine authorship of classroom documents. If an author is listed on the document, use that. If the resource is clearly a product of Walden (such as the course-based videos), use Walden University as the author. If you are unsure or if no author is indicated, place the title in the author spot, as above.
• If you cannot determine a date of publication, you can use n.d. (for "no date") in place of the year.

Note:  The web location for Walden course materials is not directly retrievable without a password, and therefore, following APA guidelines, use the main URL for the class sites: https://class.waldenu.edu.

Citing Tempo Classroom Resources

Clear author: 

Smith, A. (2005). Health effects of exposure to forest fires [PowerPoint slides]. Walden University Brightspace. https://mytempo.waldenu.edu

Unclear author:

Health effects of exposure to forest fires [Lecture notes]. (2005). Walden University Brightspace. https://mytempo.waldenu.edu

Conference Sessions and Presentations

Feinman, Y. (2018, July 27). Alternative to proctoring in introductory statistics community college courses [Poster presentation]. Walden University Research Symposium, Minneapolis, MN, United States. https://scholarworks.waldenu.edu/symposium2018/23/

Torgerson, K., Parrill, J., & Haas, A. (2019, April 5-9). Tutoring strategies for online students [Conference session]. The Higher Learning Commission Annual Conference, Chicago, IL, United States. http://onlinewritingcenters.org/scholarship/torgerson-parrill-haas-2019/

Dictionary Entry

Merriam-Webster. (n.d.). Leadership. In Merriam-Webster.com dictionary . Retrieved May 28, 2020, from https://www.merriam-webster.com/dictionary/leadership

When constructing a reference for an entry in a dictionary or other reference work that has no byline (i.e., no named individual authors), use the name of the group—the institution, company, or organization—as author (e.g., Merriam Webster, American Psychological Association, etc.). The name of the entry goes in the title position, followed by "In" and the italicized name of the reference work (e.g., Merriam-Webster.com dictionary , APA dictionary of psychology ). In this instance, APA 7 recommends including a retrieval date as well for this online source since the contents of the page change over time. End the reference entry with the specific URL for the defined word.

Discussion Board Post

Osborne, C. S. (2010, June 29). Re: Environmental responsibility [Discussion post]. Walden University Canvas.  https://waldenu.instructure.com  

Dissertations or Theses

Retrieved From a Database

Nalumango, K. (2019). Perceptions about the asylum-seeking process in the United States after 9/11 (Publication No. 13879844) [Doctoral dissertation, Walden University]. ProQuest Dissertations and Theses.

Retrieved From an Institutional or Personal Website

Evener. J. (2018). Organizational learning in libraries at for-profit colleges and universities [Doctoral dissertation, Walden University]. ScholarWorks. https://scholarworks.waldenu.edu/cgi/viewcontent.cgi?article=6606&context=dissertations

Unpublished Dissertation or Thesis

Kirwan, J. G. (2005). An experimental study of the effects of small-group, face-to-face facilitated dialogues on the development of self-actualization levels: A movement towards fully functional persons [Unpublished doctoral dissertation]. Saybrook Graduate School and Research Center.

For further examples and information, see APA 7, Section 10.6.

Legal Material

For legal references, APA follows the recommendations of The Bluebook: A Uniform System of Citation , so if you have any questions beyond the examples provided in APA, seek out that resource as well.

Court Decisions

Reference format:

Name v. Name, Volume Reporter Page (Court Date). URL

Sample reference entry:

Brown v. Board of Education, 347 U.S. 483 (1954). https://www.oyez.org/cases/1940-1955/347us483

Sample citation:

In Brown v. Board of Education (1954), the Supreme Court ruled racial segregation in schools unconstitutional.

Note: Italicize the case name when it appears in the text of your paper.

Name of Act, Title Source § Section Number (Year). URL

Sample reference entry for a federal statute:

Individuals With Disabilities Education Act, 20 U.S.C. § 1400 et seq. (2004). https://www.congress.gov/108/plaws/publ446/PLAW-108publ446.pdf

Sample reference entry for a state statute:

Minnesota Nurse Practice Act, Minn. Stat. §§ 148.171 et seq. (2019). https://www.revisor.mn.gov/statutes/cite/148.171

Sample citation: Minnesota nurses must maintain current registration in order to practice (Minnesota Nurse Practice Act, 2010).

Note: The § symbol stands for "section." Use §§ for sections (plural). To find this symbol in Microsoft Word, go to "Insert" and click on Symbol." Look in the Latin 1-Supplement subset. Note: U.S.C. stands for "United States Code." Note: The Latin abbreviation " et seq. " means "and what follows" and is used when the act includes the cited section and ones that follow. Note: List the chapter first followed by the section or range of sections.

Unenacted Bills and Resolutions

(Those that did not pass and become law)

Title [if there is one], bill or resolution number, xxx Cong. (year). URL

Sample reference entry for Senate bill:

Anti-Phishing Act, S. 472, 109th Cong. (2005). https://www.congress.gov/bill/109th-congress/senate-bill/472

Sample reference entry for House of Representatives resolution:

Anti-Phishing Act, H.R. 1099, 109th Cong. (2005). https://www.congress.gov/bill/109th-congress/house-bill/1099

The Anti-Phishing Act (2005) proposed up to 5 years prison time for people running Internet scams.

These are the three legal areas you may be most apt to cite in your scholarly work. For more examples and explanation, see APA 7, Chapter 11.

Magazine Article

Clay, R. (2008, June). Science vs. ideology: Psychologists fight back about the misuse of research. Monitor on Psychology , 39 (6). https://www.apa.org/monitor/2008/06/ideology

Note that for citations, include only the year: Clay (2008). For magazine articles retrieved from a common academic research database, leave out the URL. For magazine articles from an online news website that is not an online version of a print magazine, follow the format for a webpage reference list entry.

Newspaper Article (Retrieved Online)

Baker, A. (2014, May 7). Connecticut students show gains in national tests. New York Times . http://www.nytimes.com/2014/05/08/nyregion/national-assessment-of-educational-progress-results-in-Connecticut-and-New-Jersey.html

Include the full date in the format Year, Month Day. Do not include a retrieval date for periodical sources found on websites. Note that for citations, include only the year: Baker (2014). For newspaper articles retrieved from a common academic research database, leave out the URL. For newspaper articles from an online news website that is not an online version of a print newspaper, follow the format for a webpage reference list entry.

OASIS Resources

Oasis webpage.

OASIS. (n.d.). Common reference list examples . Walden University. https://academicguides.waldenu.edu/writingcenter/apa/references/examples

For all OASIS content, list OASIS as the author. Because OASIS webpages do not include publication dates, use “n.d.” for the year.

Interactive Guide

OASIS. (n.d.). Embrace iterative research and writing [Interactive guide]. Walden University. https://academics.waldenu.edu/oasis/iterative-research-writing-web

For OASIS multimedia resources, such as interactive guides, include a description of the resource in brackets after the title.

Online Video/Webcast

Walden University. (2013).  An overview of learning  [Video]. Walden University Canvas.  https://waldenu.instructure.com  

Use this format for online videos such as Walden videos in classrooms. Most of our classroom videos are produced by Walden University, which will be listed as the author in your reference and citation. Note: Some examples of audiovisual materials in the APA manual show the word “Producer” in parentheses after the producer/author area. In consultation with the editors of the APA manual, we have determined that parenthetical is not necessary for the videos in our courses. The manual itself is unclear on the matter, however, so either approach should be accepted. Note that the speaker in the video does not appear in the reference list entry, but you may want to mention that person in your text. For instance, if you are viewing a video where Tobias Ball is the speaker, you might write the following: Tobias Ball stated that APA guidelines ensure a consistent presentation of information in student papers (Walden University, 2013). For more information on citing the speaker in a video, see our page on Common Citation Errors .

Taylor, R. [taylorphd07]. (2014, February 27). Scales of measurement [Video]. YouTube. https://www.youtube.com/watch?v=PDsMUlexaMY

OASIS. (2020, April 15). One-way ANCOVA: Introduction [Video]. YouTube. https://youtu.be/_XnNDQ5CNW8

For videos from streaming sites, use the person or organization who uploaded the video in the author space to ensure retrievability, whether or not that person is the speaker in the video. A username can be provided in square brackets. As a change from APA 6 to APA 7, include the publisher after the title, and do not use "Retrieved from" before the URL. See APA 7, Section 10.12 for more information and examples.

See also reference list entry formats for TED Talks .

Technical and Research Reports

Edwards, C. (2015). Lighting levels for isolated intersections: Leading to safety improvements (Report No. MnDOT 2015-05). Center for Transportation Studies. http://www.cts.umn.edu/Publications/ResearchReports/reportdetail.html?id=2402

Technical and research reports by governmental agencies and other research institutions usually follow a different publication process than scholarly, peer-reviewed journals. However, they present original research and are often useful for research papers. Sometimes, researchers refer to these types of reports as gray literature , and white papers are a type of this literature. See APA 7, Section 10.4 for more information.

Reference list entires for TED Talks follow the usual guidelines for multimedia content found online. There are two common places to find TED talks online, with slightly different reference list entry formats for each.

TED Talk on the TED website

If you find the TED Talk on the TED website, follow the format for an online video on an organizational website:

Owusu-Kesse, K. (2020, June). 5 needs that any COVID-19 response should meet [Video]. TED Conferences. https://www.ted.com/talks/kwame_owusu_kesse_5_needs_that_any_covid_19_response_should_meet

The speaker is the author in the reference list entry if the video is posted on the TED website. For citations, use the speaker's surname.

TED Talk on YouTube

If you find the TED Talk on YouTube or another streaming video website, follow the usual format for streaming video sites:

TED. (2021, February 5). The shadow pandemic of domestic violence during COVID-19 | Kemi DaSilvalbru [Video]. YouTube. https://www.youtube.com/watch?v=PGdID_ICFII

TED is the author in the reference list entry if the video is posted on YouTube since it is the channel on which the video is posted. For citations, use TED as the author.

Walden University Course Catalog

To include the Walden course catalog in your reference list, use this format:

Walden University. (2020). 2019-2020 Walden University catalog . https://catalog.waldenu.edu/index.php

If you cite from a specific portion of the catalog in your paper, indicate the appropriate section and paragraph number in your text:

...which reflects the commitment to social change expressed in Walden University's mission statement (Walden University, 2020, Vision, Mission, and Goals section, para. 2).

And in the reference list:

Walden University. (2020). Vision, mission, and goals. In 2019-2020 Walden University catalog. https://catalog.waldenu.edu/content.php?catoid=172&navoid=59420&hl=vision&returnto=search

Vartan, S. (2018, January 30). Why vacations matter for your health . CNN. https://www.cnn.com/travel/article/why-vacations-matter/index.html

For webpages on the open web, include the author, date, webpage title, organization/site name, and URL. (There is a slight variation for online versions of print newspapers or magazines. For those sources, follow the models in the previous sections of this page.)

American Federation of Teachers. (n.d.). Community schools . http://www.aft.org/issues/schoolreform/commschools/index.cfm

If there is no specified author, then use the organization’s name as the author. In such a case, there is no need to repeat the organization's name after the title.

In APA 7, active hyperlinks for DOIs and URLs should be used for documents meant for screen reading. Present these hyperlinks in blue and underlined text (the default formatting in Microsoft Word), although plain black text is also acceptable. Be consistent in your formatting choice for DOIs and URLs throughout your reference list.

Related Resources

Knowledge Check: Common Reference List Examples

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Referencing: About End-Text References

End-text references.

A reference list contains the information a reader needs to be able to identify and retrieve works cited in a text. This information is in the form of end-text references.

End-text references comprise four elements:

• Author :   who is responsible for this work? An author may be an individual; multiple people; a group (government agency, organisation or institution); or a combination of groups and people.
• Date :   when was the work published? Date of publication can be year only; year, month and day (exact date); year and month; year and season; or a range of dates (e.g. range of years).
• Title :   what is the work called? There are two categories of titles: works that stand alone (e.g. reports, whole books, data sets, webpages, and films), and works that are part of a greater whole (e.g. edited book chapters, podcast and television episodes, and journal articles). 
• Source :   where can I find the work? This might be a publisher, a web address/URL, or both.

End each element with a full stop, with the exception of the URL or DOI (adding a full stop can interfere with accessing the content using the link).

These elements come together to form an end-text citation that follows this format: 

Author. (Date).  Title of the work . Source.

Example of an end-text citation for a whole book with no DOI

Grellier, J., & Goerke, V. (2018). Communications toolkit (4th ed.). Cengage Learning Australia.

For a brief (6-minute) introduction to end-text referencing, view the video below:

See below for the specific rules for formatting each element, from author to source (including URLs).

For information about formatting the reference list as a whole, see the page  Reference List .

There are some variations to this general reference format depending on the type of work you are citing. Reference Examples can help you format a variety of reference types.

Reference Examples

Specific reference examples.

Examples of types of works that you might want to reference. 

• Journal articles
• Newspaper articles
• Magazine articles
• Proprietary databases
• Chapters in a book
• Encyclopaedia entries
• Dictionary entries
• Wikipedia entries
• Republished editions of a book
• Translated books
• United Nations Reports
• Technical reports or standards
• Conference papers
• Code of ethics
• Thesis/dissertation
• TV episodes
• YouTube or streaming videos
• Plays or performances
• Music recordings
• Software or mobile apps
• Online news sources
• Lecture notes and class materials
• Social media
• Format the author's name as family name, comma, first initials. Each initial is separated by a space.
• If the author is an organisation, provide its full name, even if it is abbreviated elsewhere. See below for more information.
• If two authors are both group authors, do not use a comma between them.
• Include up to 20 authors. If a work has more than 20, provide the first 19 authors, an ellipsis (. . .), and then the final name. Do not include an ampersand. The Quick Guide PDF has an example of a work with more than 20 authors.
• A full stop goes at the end of the author element (unless one is there already).

Author, A., Author, B. B., & Author, C.

Bureau of Meteorology & Commonwealth Scientific and Industrial Research Organisation.

When the author is a group, such as a company or a government department, you should provide its full name in the end-text reference, even if it is abbreviated elsewhere. Deciding what counts as its full name can be tricky. You might need to look for an "About Us" or similar page to find out how the organisation should be credited. Visit the APA Style website for more information.

• If a webpage or report is on a government or company website, you should generally use the organisation as the author.
• Sometimes both an individual and a group seem to be the author. If there is a person listed prominently on the work (e.g. on the cover, title page, suggested citation, or the top of an article), that is usually the author; the group would then act as the 'publisher'. Use your judgment to decide who is being presented as the author, and which author would help someone else find the work using your reference.
• If multiple layers of government agencies are listed as the author, use the most specific agency as the author, and include the parent agencies in the source element as 'publisher'.
• Do not include jurisdiction (e.g. Commonwealth of Australia) unless it is needed to distinguish between two organisations that would otherwise have the same name.

The National Cancer Institute is a US-based group which is part of the National Institutes of Health, which is itself part of the Department of Health and Human Services. The author should be only the most specific group:

National Cancer Institute.

The full reference would include the parent bodies as the 'publisher', ordered starting from the largest level, and separated by commas:

National Cancer Institute. (Date). Title of the work . Department of Health and Human Services, National Institutes of Health. https://www......

Specialised roles

Some reference types, such as films or edited books, routinely credit major contributors who would not be described as the 'author' of the work. For these contributors, include their role in parentheses after their name in the end-text reference. (Do  not  include the role in the in-text citation.) If the role is editor, it should be abbreviated as (Ed.), or (Eds.) for multiple editors.

Scott, R. (Director).

Cunningham, S., & Turner, G. (Eds.).

Saunders, A. (Host).

Patterson, J. (with Marklund, L.).

If you can not find the author of a work, including a group or organisation that is responsible for the work, use the title in place of the author. The title spot can be left blank. (Formatting for in-text citation is available  here .)

Do not cite the author as "Anonymous" unless the work was published under that pseudonym.

Italian government declares state of emergency in flood-ravaged Venice. (2019, November 15).  The Age . https://www.theage.com.au/world/europe/italian-government-set-to-declare-state-of-emergency-in-venice-20191115-p53ast.html

Unusual spelling & capitalisation, and titles & ranks

Use the spelling and capitalisation the author uses.

de la Cruz, J.

Johnson-Lee, H., & Johnson Vasquez, L.

If an author's first name is hyphenated, include both initials and the hyphen if both names are capitalised.

Young-Ha Kim ⇒ Kim, Y.-H.

Lee-ann Raboso ⇒ Raboso, L.

Do not include titles and ranks, unless they are part of the author's name.

John Smith, Jr ⇒  Smith, J., Jr.

John Smith, M.D., Ph.D.  ⇒ Smith, J.

Lady Gaga  ⇒ Lady Gaga.

If the real name of someone who usually publishes under a username is known, give the real name first but include the username in brackets:

Dorsey, J. [@jack].

Only the family name will be included in in-text citations: (Dorsey, 2020).

If only the username is known, do not put it in brackets. The username will be treated as the author's name for in-text and end-text citations, e.g. (mt2mt2, 2015).

Give the date the item was published - usually just the year.

For some items that are published more frequently, such as webpages and newspaper articles, a more specific date is required (if available) to help the reader find the specific work you are citing.

Formatting this element

The date goes within parentheses:

(2012, May 18).

(2019, Spring).

Note that the copyright date at the footer of a webpage is usually not the date the content was published.

If you can not find the publication date for an item, use the abbreviation for "no date":

Titles usually do not keep the same formatting as the original source. Keep the original spelling, but capitalisation and italics in titles are standardised to fit the APA style rules. 

Formatting: italics

Titles of stand-alone publications (works that are complete in themselves, like a whole book or a report) are formatted in italics in your end-text references. Titles of items that are part of a larger work (such as articles and chapters) are not in italics.

Stand-alone work:

Project management: The managerial process.

Part of a greater work:

Italian government declares state of emergency in flood-ravaged Venice.

Formatting: capitalisation

There are two types of capitalisation used in APA style referencing:

• Sentence case: Most words are lowercase, except: the first word of the title, the first word of any subtitles, proper nouns (e.g. places and people), and acronyms.
• Title case: Capitalise the first word of the title, the first word of any subtitles, any major or content words, and any word with four or more letters.

Most titles in your end-text referencing will be in sentence case. If you are mentioning the title of a journal as a whole, a newspaper or magazine, an organisation's name, or a publisher, these will usually be in title case.

Sentence case:

The role of occupation in an integrated boycott model: A cross-regional study in China.

Title case:

Health Promotion Journal of Australia.

Gone With the Wind.

Jump to information about:

Edition, report, or volume number

Unusual formats

Original work in another language

Republished or translated works

Works with an edition, report, or volume number

If a work has an edition, report, or volume number, include it in parentheses after the title. Do not put a full stop between the title and this descriptive information. This element is not in italics, even if the title is.

• Use the abbreviation "ed." for edition, and "Vol." for volume.
• Edition is written with numbers, not in superscript: use "6th ed.", not "Sixth ed." or "6 th  ed." Revised edition is abbreviated to "Rev. ed."
• For reports, give the report number as it appears on the work, as in the second and third examples below.

Effective security management (6th ed.).

Land management and farming in Australia, 2014-15 (Cat. No. 4627.0).

Foundation to year 10 curriculum: Language for interaction (ACELA1428).

If there is both a volume and an edition, the edition comes first.

Clinical nutrition (2nd ed., Vol. 3).

Works with an unusual format

If the format is something unusual for an academic context (something other than books, journal articles, and reports), you can include a description of the format after the title. The description will not be in italics, even if the title is.

Guide to the wildflowers of Perth [Brochure].

Don't let me be misunderstood [Song].

Journeys towards expertise in technology-supported teaching [Doctoral dissertation, Edith Cowan University].

Works with no title

If the work has no title, use a description of the work in square brackets.

[Map showing local Perth election results in 2018].

Do not use italics for your description, even if the title would usually be in italics.

If this is a work with an unusual format (e.g. Photograph, Lecture recording, or Map), you can include the type as part of the description.

Works in another language

Before you use a work in another language as a reference for an assignment, check with your unit coordinator that this is acceptable. They might prefer that you find an English-language source so that they can check the reference for themselves.

If you are citing a work in a language other than the language of your own writing, and you read that work in its original language, you should include a translation of the title element. The translated title does not need to be literal: it should inform the reader what the work is about. The translation should be within square brackets, following the original title, and is not italicised even if the title is.

Schweriner Café-Besucher tragen Schwimmnudel-Hüte [Visitors to Schwerin cafe wear pool noodle hats for social distancing].

Nihongo no goi tokusei  [Lexical characteristics of Japanese language].

All other details should be written in the original language. This will make it easier to locate the source. If the language does not use the Roman alphabet (for instance, if it is written in a language like Hindi, Mandarin, or Arabic; or in Japanese, as in the example above), you should transliterate those details into the Roman alphabet if possible.

Republished or translated works

If a work has been republished in a different year, include information about the original publication date at the end of the reference. If other creators had a significant role in creating the new edition, include information about the editor, translator, or (as below) narrator in parentheses after the title; if the type of work needs explanation, include the type in square brackets. These elements are not in italics, even if the title is. There should be no full stop between the title and extra information in the title element, or after the original publication date.

An example of this sort of work might be an ebook published in a different year to the original book, a version translated into a new language or format, or a new edition of a classic book; this is not intended for reprints of the same work by the same publisher soon after publication.

Heller, J. (2008). Catch-22 (T. White, Narr.) [Audiobook]. Hachette Audio UK. (Original work published 1961)

Both dates will appear in the in-text reference for these works: (Heller, 1961/2008).

The source of a work is usually:

• The publisher, parent body of an organisation, or overarching website for a webpage

Note that an item might have both a publisher/website and a URL or DOI.

If the publisher is the same group or individual as the author, do not duplicate the information in your reference. You should still include a DOI or URL if appropriate.

Bureau of Meteorology. (2019). Monthly weather review: Australia: September 2019. http://www.bom.gov.au/climate/mwr/aus/mwr-aus-201909.pdf

Bureau of Meteorology is both the author and the publisher of this report, so the reference does not have a publisher listed in the source.

DOI/URL notes

• Do not place a full stop after a DOI or URL.
• If there is a DOI, always include it. You do not need to include a URL if there is a DOI.
• If using a URL, use a permanent link if there is one. If possible, link directly to the work you used.
• URLs and DOIs should be live (the reader should be able to click the link), but whether they look like hyperlinks (blue and underlined) or like the rest of your text is a style decision that you can make. Check your assignment guidelines or ask your lecturer if they have a preference.
• DOI should be displayed in the format: https://doi.org/10.xxxx

Oxford University Press.

Australian Institute of Criminology. https://aic.gov.au/publications/special/005

https://doi.org/10.1534/g3.114.015966

YouTube. https://www.youtube.com/charlie#p/u/4/qjIsdbBsE8g

URL shorteners

APA style now allows link shorteners  where a link is overly complex or long.

• This advice is aimed largely at student papers: it is usually not appropriate for publication or theses.
• Some URL shorteners only work for a few days, so make sure the link will work for as long as you need it to, including marking and potential appeal periods.
• Check that shortened links are acceptable for your assignment.
• There is no requirement to shorten a URL . Even if a link is very long, you can include it in your reference list.

A URL shortener will take a long URL and make it look more like this:

http://tiny.cc/sp4gpz

Some websites have their own short links that you can use, specific to their site.

APA 7 Tutorial: DOIs and URLs

Learn how to use the two types of electronic retrieval information found in references, digital object identifiers (DOIs) and uniform resource locators (URLs), including how to cite documents retrieved from research databases and websites.

Academic Writer, © 2020 American Psychological Association.

No author

If a work seems to have no author, check to see if an organisation or group might be responsible for it. If there is not a clear group author either, you should use the title in place of the author.

Use the title, or the first few words of the title if it is long, in your in-text citations as well.

The date in a citation refers to the date the content was published. If you can't locate this information, use the abbreviation for "no date" in place of the year: n.d.

Use this abbreviation in your in-text citations as well.

If there is no title, use a description of the work in square brackets.

If the work would usually have a type (e.g. Photograph, Data set, Recording of a play) in brackets after the title, you can include that in the title description.

If a work you used is not available to the intended audience of your assignment or project, consider whether it is appropriate to use it as evidence.

If you decide to use it, you should cite the work as personal communication . This sort of citation does not have a reference list entry, because a reader would not be able to locate the work you used. It uses only in-text citations, with a slightly different format to normal in-text citations.

If you are using your own research data, see Section 8.36 in the APA manual.

In general, cite: 

• what is available on the work you are citing, and
• what would make it easy for another person to find that work.

You should have some information for each of the four elements (author, date, title, source), but if a detail does not exist, leave it off.

Missing reference information on the APA Style website.

APA 7 Tutorial: Missing Reference Elements

Learn about the four reference elements of an APA Style reference: the author, date, title, and source.

What Is a DOI?

If there is a DOI for a source you are citing, include it at the end of your reference. This takes the place of a URL.

A digital object identifier ( DOI ) is a unique code used to identify content and provide a persistent link to a document on the internet. A publisher assigns a DOI when a journal article is published and made available electronically.

A DOI will usually be found on the source near other reference elements like title and author. For APA style referencing, you should put the DOI in the following format:

https://doi.org/10.5468/ogs.2016.59.1.1

Make sure the DOI does not include EZProxy in the URL. It should just be https://doi.org/10.xxxx. If the DOI is not already in URL format (for instance, the example above might just say DOI: 10.5468/ogs.2016.59.1.1), you can attach "https://doi.org/" to the front of the DOI number.

For further information, refer to Crossref or the APA's Academic Writer tutorial below. Read the information about URL shorteners under Source: formatting and notes above before using a short DOI.

• Crossref's display guidelines
• Academic Writer Quick Guide: DOIs and URLs
• DOI link shorteners
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Common Abbrevations

Some words and phrases are abbreviated in all end-text references in APA style. Here's a list of common abbreviations from Section 9.50 of the Manual . Take note of capitalisation and punctuation.

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• Last Updated: May 23, 2024 12:13 PM
• URL: https://ecu.au.libguides.com/referencing

Edith Cowan University acknowledges and respects the Noongar people, who are the traditional custodians of the land upon which its campuses stand and its programs operate. In particular ECU pays its respects to the Elders, past and present, of the Noongar people, and embrace their culture, wisdom and knowledge.

How to Write References and Cite Sources in a Research Paper

Table of contents

• 1.1 Academic Integrity
• 1.2 Avoiding Plagiarism
• 1.3 Building Credibility
• 1.4 Facilitating Further Research
• 2.1 APA (American Psychological Association)
• 2.2 MLA (Modern Language Association)
• 2.3 Chicago Style
• 2.4 IEEE (Institute of Electrical and Electronics Engineers)
• 3.1 Author(s)
• 3.2 Title of the Source
• 3.3 Publication Date
• 3.4 Publisher
• 3.5 Page Numbers
• 3.6 DOI (Digital Object Identifier) or URL (Uniform Resource Locator)
• 4.1.3 Chicago
• 4.2.1 Citing Multiple Authors
• 4.2.4 Chicago
• 4.3 Page Numbers in In-Text Citations
• 5.1 Formatting and Organizing Your References
• 5.2 Alphabetizing Your References
• 5.3.2 Journal
• 5.3.3 Chapter
• 5.3.4 Conference Paper/Presentation
• 5.3.5 Online Sources
• 6.1 Verify Your Source
• 6.2 Follow the One Style Guide
• 6.3 Verify DOI and URLs
• 6.4 Online Citation Generators
• 6.5 Use University Libraries and Writing Centers
• 7 Leave No Stone Unturned!

Citation is necessary while writing your school essay, a publication, or a Master’s thesis. We all want our efforts to be acknowledged, right? The lack of references and citations can make the source think you are trying to steal their work. Hence, the question is how to go about making references.

Do you want to learn how to cite in a research paper? Then this article is for you, as it contains the details of how to reference when writing a research paper. There is a standard way to do this in educational journals and organizational publications.

Hence, a researcher must understand how to reference their writings or journals. It is another thing to write a journal properly, but crediting the sources is more crucial.

Follow this guide to learn:

• The importance of referencing and citations for your academic works;
• How to cite in APA, MLA, Chicago, IEEE, and ASA styles;
• Essential guidelines to follow for a published work.

Why Referencing and Citation Matter

Another important question is: What is the need for referencing and citation? The major reason for citations in research paper format is to serve as directional cues for the employed knowledge. When you cite, readers can know that some portions of your content belong to you. Hence, it is easier to identify how recent the information is.

Citation for your paper comes with several advantages. They include:

Academic Integrity

The citation affirms the integrity of your academic writing. In this information age, there are several details, and it can be difficult to authenticate. When you reference, it helps readers understand the necessity of the discussed topic. Referencing certain authors can give more authority to your papers.

Avoiding Plagiarism

Plagiarism refers to the mindless lifting of details from another material without acknowledging the details. For the source, they could believe you are stealing from them. In most countries, copyright infringement is a punishable crime and can make you lose your hard work.

Building Credibility

Credibility is the goal of every academic scholar. There is no better way to gain relevance than by citing sources from other credible ones.

Facilitating Further Research

For other researchers like you, providing citations can serve as other sources for more information. It helps them to know other philosophies about the subject.

Choosing the Right Citation Style

Now that the advantages have been established, the new worry is the choice of the right style. There are several styles with their respective peculiarities. For example, the MLA writing style is common in liberal scientific paper citations. Let’s delve more into MLA formatting for research papers and other styles.

APA (American Psychological Association)

The commonest style used by many scholars is APA formatting , especially if there is no stated style. This approach employs the use of in-text citations to explain the source. It’s the simplest form of citation.

Here is an in-text referencing example:

“Exercise is a good way to recover from ailments.” APA, n.d. (American Psychological Association).

The reference style includes:

• The author’s name;
• The author’s name is in parenthesis to follow the referenced excerpt;
• The publication date.

MLA (Modern Language Association)

MLA-style formation is concise and known for its scientific referencing format. The peculiarity of the MLA citation is its source citation, episode title, and document layout. You have to:

• Include the parenthetical citation;
• Create some spaces away from the left margin;
• Include the author’s or source’s name.

Ensure you capitalize every word when including the names. You can employ professional MLA Citation Generators to make the compilation easier. It is perfect for the citation format of scientific papers.

Chicago Style

Chicago’s style is famous for two things:

• The in-text citation within the paper;
• The reference list is at its end.

It is an author-date approach. Hence, the in-text citation for a research paper has the author’s or source name and publication year.

IEEE (Institute of Electrical and Electronics Engineers)

This employs the use of numbers. It is chronological as it arranges the citation based on the order of appearance. A click on it takes the reader to the full reference at the end of the paper. To make it easier, you can employ IEEE Citation Maker for a well-curated task. This way, you won’t have to worry about the manual compilation of the IEEE citation style.

This is similar to the author-date approach by Chicago Style. You can:

• Create the quotation;
• Include the parentheses for the author’s name and publication date;
• Add the page number using a colon.

Components of a Citation

Do you want to know how to complete a citation for your professional research paper writing service and research paper? Learn about its components.

The author is also regarded as the source. It is the original writer of the material you are referencing. Sometimes, there may be multiple authors. Do not miss out on anyone while citing a research paper.

Title of the Source

The title of the source is often the name given to the material by the author.

Publication Date

As the name implies, this refers to the date the source was published. Frequently, most writers include it at the start of their material. State the exact month and year of publication, separated with a comma. See example:

“(2016, March 7).”

Including the publisher’s details is only necessary for the full reference. It should be at the end of the paper. It can facilitate further research.

Page Numbers

The page number is necessary, as it helps to easily refer to different sections of the paper.

DOI (Digital Object Identifier) or URL (Uniform Resource Locator)

A DOI is a link to a resource on the internet. The resource can be a book or its chapter. On the other hand, a URL is an address that indicates where the resource can be found. It helps to locate the resource. The use of URLs and DOIs directs readers to the digital identifier of the source.

In-Text Citations

An in-text citation for a research paper is the brief form of the bibliography that you include in the body of the content. It contains the author’s family name and year of publication. It provides enough details to help users know the source in their reference list. Each citation format for research papers is unique.

See citation examples below.

How to Cite Direct Quotations for Each Citation Style

The general rule in referencing is that in-text citations must have a corresponding entry in your reference list. Let’s see how!

There are two types of APA in-text citations:

Parenthetical:

The researchers concluded, “Climate change poses significant challenges for coastal communities” (Johnson & Lee, 2021, p. 78).

In their study on the effects of exercise on mental health, Smith and Johnson (2019) found that regular physical activity was associated with a significant decrease in symptoms of anxiety and depression. According to their research, engaging in exercise three times a week for at least 30 minutes had a positive impact on participants’ overall well-being.

APA in-text citation style employs the source’s name and publication year. A direct quotation will include the page number. Remember, you can generate a citation in a research paper using the APA style via a citation generator.

MLA is known as the scientific style of citation. The uniqueness of MLA Style formatting is the use of a direct quote (in quotes), the Author’s name and page number (in parentheses).

In the novel “To Kill a Mockingbird,” Atticus Finch imparts wisdom to his children, saying, “You never really understand a person until you consider things from his point of view… until you climb into his skin and walk around in it” (Lee 30).

For Chicago, you are to include a parenthetical citation, the author’s name, the publication year, and the quote’s page number.

As Adams (2009) argues, “History is a vast early warning system” (53).

IEEE (Institute of Electrical and Electronics Engineers) style typically uses numerical citations in square brackets for in-text citations. It doesn’t rely heavily on direct quotations in the same way as some other citation styles, like APA or MLA. Instead, IEEE generally prefers paraphrasing and citing the source, but direct quotations can be used when necessary. Here’s an example of a direct quotation in IEEE style:

In-Text Citation:

As stated by Smith, “In most cases, the impedance of the transmission line remains relatively constant throughout its length” [1].

Corresponding Reference Entry:

[1] A. Smith, “Transmission Line Impedance Analysis,” IEEE Transactions on Electrical Engineering, vol. 45, no. 3, pp. 212-225, 2010.

ASA is different because it contains the author’s name, publication year, and even the page number.

According to Smith (2010), “Social institutions shape our behaviors and interactions in profound ways” (p. 45).

How to Cite Paraphrased Information

While writing a college paper, paraphrasing is important to achieve clarity, but it is ideal to cite the source of the paraphrased information. The proper way to cite paraphrased information is to include a parenthetical citation. The style of referencing for all citation styles doesn’t change, but they should be in parenthesis.

“Strength can be defined in terms of ability and acquired skills, according to (Jack et al. 2023).

Citing Multiple Authors

The technique is different when you are citing a source that has multiple authors. For the first-time citation, you should include the names of all the authors. The subsequent activities to generate a citation in APA should only include the first author’s surname and the proper use of ‘et al.’ However, you should include the surname and initials of all these authors in the full reference. Separate the authors with commas and ampersands before the final name.

Two Authors:

When a source has two authors, include both authors’ names in the in-text citation every time you reference the source. Use an ampersand (&) between the authors’ names, and include the year of publication in parentheses. For example:

(Smith & Johnson, 2020) found that…

Three to Five Authors:

When a source has three to five authors, list all authors in the first in-text citation. Use an ampersand (&) between the last two authors’ names. For subsequent citations of the same source, use only the first author’s name followed by “et al.” and the year. For example:

First citation: (Smith, Johnson, & Williams, 2018)…

Subsequent citations: (Smith et al., 2018)…

Six or More Authors:

When a source has six or more authors, you should use “et al.” in both the first and subsequent in-text citations, along with the year. For example:

(Smith et al., 2019) conducted a study on…

Group Authors:

When citing sources authored by a group, organization, or company, use the full name of the group or organization as the author in the in-text citation. If the abbreviation is well-known, you can use the abbreviation in subsequent citations. For example:

First citation: (American Psychological Association [APA], 2019)…

Subsequent citations: (APA, 2019)

When a source has two authors, include both authors’ names in the in-text citation, separated by the word “and.” For example:

(Smith and Johnson 45) found that…

Three or More Authors:

When a source has three or more authors, include only the first author’s name followed by “et al.” in the in-text citation. For example:

(Smith et al. 72) conducted a study on…

If a source has no identifiable author, use a shortened version of the title in the in-text citation. Enclose the title in double quotation marks or use italics if it’s a longer work (e.g., a book or film). For example:

(“Title of the Source” 28) argues that…

(American Psychological Association 62) states that…

Author-Date System:

In the Author-Date system, when a source has two authors, include both authors’ last names and the publication year in parentheses in the in-text citation, separated by an ampersand (&). For example:

(Smith & Johnson 2020) found that…

When a source has three or more authors, you can use “et al.” after the first author’s name in the in-text citation. For example:

(Smith et al. 2018) conducted a study on…

Notes and Bibliography System:

In the Notes and Bibliography system, when a source has two authors, include both authors’ full names in the note. For example:

John Smith and Jane Johnson, Title of the Work (Place of Publication: Publisher, Year), page number.

When a source has three or more authors, list the first author’s name followed by “et al.” in the note. For example:

John Smith et al., Title of the Work (Place of Publication: Publisher, Year), page number.

When a source has two authors, include both authors’ last names in the in-text citation, separated by the word “and.” For example:

(Smith and Johnson 2020) found that…

Three Authors:

When a source has three authors, include all three authors’ last names in the in-text citation, separated by commas. For example:

(Smith, Johnson, and Williams 2018) conducted a study on…

More than Three Authors:

When a source has more than three authors, you should use the first author’s last name followed by “et al.” in the in-text citation. For example:

(Smith et al. 2019) conducted a study on…

When a source has two authors, include both authors’ last names in the in-text citation, separated by “and.” For example:

[1] Smith and Johnson found that…

When a source has three or more authors, use the first author’s last name followed by “et al.” in the in-text citation. For example:

[2] Smith et al. conducted a study on…

Page Numbers in In-Text Citations

The use of page numbers in in-text citations is more peculiar to APA style. You can use paragraphs as indicated above if the source has no page, as seen in some e-books and websites.

Creating a Reference List or Bibliography

Creating a reference list is one of the most important tips for writing a research paper because it shows the general scheme of paper citation. This part of the content is a step-by-step process you can follow to create your reference list for your research paper.

Formatting and Organizing Your References

Formatting and organizing your references is the first step when you want to create your bibliography. You need to arrange all the full references to the in-text citation in the downward part of your paper. To avoid missing out on any, writing every full reference when you write the in-text citation is advisable.

Alphabetizing Your References

Alphabetizing your references ensures you create your bibliography in an orderly fashion for easy comprehension. Hence, you can do it numerically or alphabetically. The numerical order is dependent on the referencing system you are using, while the alphabetical order uses the author’s name to organize the reference.

Citations for Different Source Types

Different source types have their respective references, even for scientific papers. The commonest sources include books, journals, chapters, presentations, and online (to cite a website).

See how to cite an example for each source below:

Author, Initial. (Year). Book Title. City of publication, Country/State: Publisher.

“Social, M. (2023). The effect of the internet in this modern era . London, England: Ink.”

Author last name, First name. Book Title: Subtitle . Edition, Publisher, Year.

Donaldson, Bruce. Dutch: A Comprehensive Grammar . 3rd ed., Routledge, 2017..

Author last name, First name. Book Title: Subtitle . Edition. Place of publication: Publisher, Year. E-book format.

Donaldson, Bruce. Dutch: A Comprehensive Grammar . 3rd ed. Abingdon-on-Thames: Routledge, 2017.

• N. Last Name, Title , Edition. City: Publisher, 2000.
• Angelou, I Know Why the Caged Bird Sings , 1st ed. New York: Random House, 1969

Quote (Name Date)

Referencing is vital in research (Smith 2020).

Author, Initial. (Year). Article Title. Journal Title. The volume of the Journal (in italics), issue number of journal in round brackets, page range of articles, URL, and first time.

Social, M. (2023). The effect of the internet in this modern era . Digital Technology, 26(8), 22-24. (Insert URL).

Author. Journal title Date, Page. DOI

Ahmed, Sara. “What is Whiteness.” Feminist Theory , vol. 8, no. 2, Aug. 2007, pp. 149–168. https://doi.org/10.1177/1464700107078139.

Author’s Last Name, First Name. “Article Title.” Journal Name Volume, No. Issue (Month or Season Year): Page range. DOI or URL.

Pickard, Hanna. “What Is Personality Disorder?” Philosophy, Psychiatry, & Psychology 18, no. 3 (September 2011): 181–84. https://doi.org/10.1353/ppp.2011.0040.

Author Initial(s) and Surname, “Article title,” Journal Title , volume number, issue number, page range, month, and year of publication.

• Chesum, “Innovations in Catalyzation,” J Adhes Sci Technol , Vol. 7, No. 1., pp. 11–24, July-September 2012.

Author Surname, Author Forename. Year Published. ‘Title’. Publication Title Volume Number (Issue Number): Pages Used. Retrieved October 10, 2013 (http://Website URL).

Sandelowski, Margarete. 1994. ‘Focus On Qualitative Methods. Notes On Transcription’. Research in Nursing \& Health 17(4):312.

Chapter Author’s Last Name, First Initial. Second Initial. (Year). Chapter or article title. Editor First Initial. Second Initial. Editor’s Last Name (Ed.). Book title: Subtitle (edition number, if not the first pages of the chapter). Location of publication: Publisher.

Social, M.O., (2023). Coarctation. In D.S. Moodie (Ed.). Management of heart disease: Indulthood (pp. 142-170). Minneapolis, Minnesota: Cardiotext Publishing.

Name. Book title: Subtitle. Editors. Location of publication: publisher.

Schwartz, Paula. “Redefining Resistance: Women in France.” Behind the Lines: Two World Wars , edited by Margaret R. Higonnet et al., Yale UP, 1987, pp. 141–53.

Author’s Last Name, First Name. “Chapter Title.” In Book Title: Subtitle , edited by Editor first name Last name, Page range. Place of publication: Publisher, Year.

Nussbaum, Martha C. “Legal Reasoning.” In The Cambridge Law , edited by John Tasioulas, 59–77. Cambridge: Cambridge University Press, 2020.

Author(s), “Chapter title,” in Book Title, Editor(s), Ed(s). City, Country: Publisher, year, p(p). page(s).

• Saito, A. Jorio, and M. S. Dresselhaus, “Properties of nanographene,” in The Oxford Book of Technology, vol. 2, Materials , A. V. NarlikarEds. Oxford, U.K.: Oxford Univ. Press, 2010, pp. 1–30.

Author’s Last Name, First Name. Year of publication. “Title of Chapter.” Pp. Numbers in Title of Book (italicized), edited by F.I. MI. Last. Location of publisher, state or province postal code or name of country (if a foreign publisher): Publisher’s Name.

Rubin, Avi. 2015. “The Slave: A Drama from the Last Century.” Pp. 87-103 in Society, Culture in Asia: The Modernities , edited by E. R. Toledano: Walter De Gruyter Incorporated.

Conference Paper/Presentation

Last name, initial (Year). Conference paper title. Editor initial, last name (Ed.), Proceedings Book Title . Place of Publication: Publisher.

Winstone, N. & Boud, D. (2017). Supporting students’ engagement: the adoption of practices in the U.K. and Australia. A nnual Conference . Newport, South Wales

Surname, First Name. “Paper Title.” Proceedings Title, Conference Location and Date , edited by Editor Name(s), Publisher, Date of Publication.

Lewis, Jack. “Literature: The Consequences of Loss.” Library Proceedings Conference, Amsterdam, 13–14 June , edited by W. Oldham, LCP Publications, 2015.

Author First Name Last Name, “Title of the Paper” (paper presentation, Conference, Location, Date of conference).

Allison Cloyd, “An Examination of College Students” (paper presentation, EasyBib Conference, New York, NY, July 30, 2014) .

Author initials. Last name, Book Title . City, Country: Publisher, Year.

• P. Hailman, Coding: Man-Made Signals . Cambridge: Harvard Univ. Press, 2008.

Author Surname, Author Forename. Year Published. ‘Title’. P. Pages Used in Publication Title . City: Publisher. Retrieved October 10, 2013 (http://Website URL).

Vargas, Jose. 2014. ‘The End Of Liberty’. Pp. 40-42 in The end . Buenos Aires: Elsevier.

Online Sources

Last Name, Initials. (Year, Month Day). Article title . Site Name. URL

The countdown: A prophecy takedown . (2020, October 19). BBC News. https://www.bbc.com/news/election-us-2020-54596667

Author’s Last Name, First Name. Title of Book . Edition, Publisher, Year of publication.

Smith, Thomas. The Citation Manual for Students: A Guide . 2nd ed., Wiley, 2020.

Author First and Last Name, Title of Book (Place of publication: publisher, year), page number(s).

Albert Einstein, The Meaning of Relativity (Princeton: Princeton University Press, 1923), 44–45.

Author initials. Last Name, Book Title . City (and state if in the U.S.), Country: Publisher, Year.

• P. Hailman, Redundancy: Man-Made Signals . Cambridge, MA, USA: Harvard Univ. Press, 2008.

Last Name, First M. Year. “Title of article.” Title of Journal volume (issue): pages.

DOI/Retrieved Month Day, Year (URL)

Granello, Paul F. 1999. “College Students’ Wellness Due to Social Support.” Journal of Counseling 2(2):110-120.

Doi: 10.1002/j.2161-1882.1999.tb00149.x.

Tips for Accuracy

The goal of citing your paper is because of the advantages stated above. As such, you should not negotiate the accuracy of your citation. Here are the tips you can follow for accurate referencing:

Verify Your Source

Confirm if your source is credible or not. It is easier to verify books, journal articles, and chapters. You should check multiple links to confirm their authenticity.

Follow the One Style Guide

Maintain a single referencing style throughout your paper. It is improper to employ multiple referencing styles. If not specified, you can consider the APA style.

Verify DOI and URLs

DOI and URLs can be tricky and sensitive. A simple error with the punctuation can make them invalid. Hence, verifying every DOI and URL with a click is advisable. Discrediting your citation format for a scientific research paper reference based on an invalid URL is not worth it.

Online Citation Generators

Thanks to the digital age, you don’t have to worry about manually compiling your reference or generating its in-text citation. You can employ online generators to do the rough work for you. In turn, you will have more time to focus on the major content of your research work.

Use University Libraries and Writing Centers

Libraries and writing centers have extensive collections of cited sources. Since books, publications, and journals are more credible sources, university libraries remain a valid source to increase the credibility of your paper.

Leave No Stone Unturned!

Referencing and citation are the best way to preserve the relevance of your academic paper. It gives it the appropriate credibility for future use. That means another writer can refer to your work over many years, even when the level of advancement may be unmatched. A well-referenced work is evergreen.

One must note that well-oriented research paper citations have a proper format. The options include APA, MLA (citation style for science), Chicago, IEEE, and ASA. If not stated, it is advisable to follow the APA formatting style, as it is the most common. However, stick with formatting while compiling cited sources for a research paper.

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Home » References in Research – Types, Examples and Writing Guide

References in Research – Types, Examples and Writing Guide

Table of Contents

References in Research

Definition:

References in research are a list of sources that a researcher has consulted or cited while conducting their study. They are an essential component of any academic work, including research papers, theses, dissertations, and other scholarly publications.

Types of References

There are several types of references used in research, and the type of reference depends on the source of information being cited. The most common types of references include:

References to books typically include the author’s name, title of the book, publisher, publication date, and place of publication.

Example: Smith, J. (2018). The Art of Writing. Penguin Books.

Journal Articles

References to journal articles usually include the author’s name, title of the article, name of the journal, volume and issue number, page numbers, and publication date.

Example: Johnson, T. (2021). The Impact of Social Media on Mental Health. Journal of Psychology, 32(4), 87-94.

Web sources

References to web sources should include the author or organization responsible for the content, the title of the page, the URL, and the date accessed.

Example: World Health Organization. (2020). Coronavirus disease (COVID-19) advice for the public. Retrieved from https://www.who.int/emergencies/disease/novel-coronavirus-2019/advice-for-public

Conference Proceedings

References to conference proceedings should include the author’s name, title of the paper, name of the conference, location of the conference, date of the conference, and page numbers.

Example: Chen, S., & Li, J. (2019). The Future of AI in Education. Proceedings of the International Conference on Educational Technology, Beijing, China, July 15-17, pp. 67-78.

References to reports typically include the author or organization responsible for the report, title of the report, publication date, and publisher.

Example: United Nations. (2020). The Sustainable Development Goals Report. United Nations.

Formats of References

Some common Formates of References with their examples are as follows:

APA (American Psychological Association) Style

The APA (American Psychological Association) Style has specific guidelines for formatting references used in academic papers, articles, and books. Here are the different reference formats in APA style with examples:

Author, A. A. (Year of publication). Title of book. Publisher.

Example : Smith, J. K. (2005). The psychology of social interaction. Wiley-Blackwell.

Journal Article

Author, A. A., Author, B. B., & Author, C. C. (Year of publication). Title of article. Title of Journal, volume number(issue number), page numbers.

Example : Brown, L. M., Keating, J. G., & Jones, S. M. (2012). The role of social support in coping with stress among African American adolescents. Journal of Research on Adolescence, 22(1), 218-233.

Author, A. A. (Year of publication or last update). Title of page. Website name. URL.

Example : Centers for Disease Control and Prevention. (2020, December 11). COVID-19: How to protect yourself and others. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html

Magazine article

Author, A. A. (Year, Month Day of publication). Title of article. Title of Magazine, volume number(issue number), page numbers.

Example : Smith, M. (2019, March 11). The power of positive thinking. Psychology Today, 52(3), 60-65.

Newspaper article:

Author, A. A. (Year, Month Day of publication). Title of article. Title of Newspaper, page numbers.

Example: Johnson, B. (2021, February 15). New study shows benefits of exercise on mental health. The New York Times, A8.

Edited book

Editor, E. E. (Ed.). (Year of publication). Title of book. Publisher.

Example : Thompson, J. P. (Ed.). (2014). Social work in the 21st century. Sage Publications.

Chapter in an edited book:

Author, A. A. (Year of publication). Title of chapter. In E. E. Editor (Ed.), Title of book (pp. page numbers). Publisher.

Example : Johnson, K. S. (2018). The future of social work: Challenges and opportunities. In J. P. Thompson (Ed.), Social work in the 21st century (pp. 105-118). Sage Publications.

MLA (Modern Language Association) Style

The MLA (Modern Language Association) Style is a widely used style for writing academic papers and essays in the humanities. Here are the different reference formats in MLA style:

Author’s Last name, First name. Title of Book. Publisher, Publication year.

Example : Smith, John. The Psychology of Social Interaction. Wiley-Blackwell, 2005.

Journal article

Author’s Last name, First name. “Title of Article.” Title of Journal, volume number, issue number, Publication year, page numbers.

Example : Brown, Laura M., et al. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence, vol. 22, no. 1, 2012, pp. 218-233.

Author’s Last name, First name. “Title of Webpage.” Website Name, Publication date, URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC, 11 Dec. 2020, https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Publication date, page numbers.

Example : Smith, Mary. “The Power of Positive Thinking.” Psychology Today, Mar. 2019, pp. 60-65.

Newspaper article

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Publication date, page numbers.

Example : Johnson, Bob. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, 15 Feb. 2021, p. A8.

Editor’s Last name, First name, editor. Title of Book. Publisher, Publication year.

Example : Thompson, John P., editor. Social Work in the 21st Century. Sage Publications, 2014.

Chapter in an edited book

Author’s Last name, First name. “Title of Chapter.” Title of Book, edited by Editor’s First Name Last name, Publisher, Publication year, page numbers.

Example : Johnson, Karen S. “The Future of Social Work: Challenges and Opportunities.” Social Work in the 21st Century, edited by John P. Thompson, Sage Publications, 2014, pp. 105-118.

Chicago Manual of Style

The Chicago Manual of Style is a widely used style for writing academic papers, dissertations, and books in the humanities and social sciences. Here are the different reference formats in Chicago style:

Example : Smith, John K. The Psychology of Social Interaction. Wiley-Blackwell, 2005.

Author’s Last name, First name. “Title of Article.” Title of Journal volume number, no. issue number (Publication year): page numbers.

Example : Brown, Laura M., John G. Keating, and Sarah M. Jones. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence 22, no. 1 (2012): 218-233.

Author’s Last name, First name. “Title of Webpage.” Website Name. Publication date. URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC. December 11, 2020. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Publication date.

Example : Smith, Mary. “The Power of Positive Thinking.” Psychology Today, March 2019.

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Publication date.

Example : Johnson, Bob. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Example : Thompson, John P., ed. Social Work in the 21st Century. Sage Publications, 2014.

Author’s Last name, First name. “Title of Chapter.” In Title of Book, edited by Editor’s First Name Last Name, page numbers. Publisher, Publication year.

Example : Johnson, Karen S. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by John P. Thompson, 105-118. Sage Publications, 2014.

Harvard Style

The Harvard Style, also known as the Author-Date System, is a widely used style for writing academic papers and essays in the social sciences. Here are the different reference formats in Harvard Style:

Author’s Last name, First name. Year of publication. Title of Book. Place of publication: Publisher.

Example : Smith, John. 2005. The Psychology of Social Interaction. Oxford: Wiley-Blackwell.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Journal volume number (issue number): page numbers.

Example: Brown, Laura M., John G. Keating, and Sarah M. Jones. 2012. “The Role of Social Support in Coping with Stress among African American Adolescents.” Journal of Research on Adolescence 22 (1): 218-233.

Author’s Last name, First name. Year of publication. “Title of Webpage.” Website Name. URL. Accessed date.

Example : Centers for Disease Control and Prevention. 2020. “COVID-19: How to Protect Yourself and Others.” CDC. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html. Accessed April 1, 2023.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Magazine, month and date of publication.

Example : Smith, Mary. 2019. “The Power of Positive Thinking.” Psychology Today, March 2019.

Author’s Last name, First name. Year of publication. “Title of Article.” Title of Newspaper, month and date of publication.

Example : Johnson, Bob. 2021. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Editor’s Last name, First name, ed. Year of publication. Title of Book. Place of publication: Publisher.

Example : Thompson, John P., ed. 2014. Social Work in the 21st Century. Thousand Oaks, CA: Sage Publications.

Author’s Last name, First name. Year of publication. “Title of Chapter.” In Title of Book, edited by Editor’s First Name Last Name, page numbers. Place of publication: Publisher.

Example : Johnson, Karen S. 2014. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by John P. Thompson, 105-118. Thousand Oaks, CA: Sage Publications.

Vancouver Style

The Vancouver Style, also known as the Uniform Requirements for Manuscripts Submitted to Biomedical Journals, is a widely used style for writing academic papers in the biomedical sciences. Here are the different reference formats in Vancouver Style:

Author’s Last name, First name. Title of Book. Edition number. Place of publication: Publisher; Year of publication.

Example : Smith, John K. The Psychology of Social Interaction. 2nd ed. Oxford: Wiley-Blackwell; 2005.

Author’s Last name, First name. Title of Article. Abbreviated Journal Title. Year of publication; volume number(issue number):page numbers.

Example : Brown LM, Keating JG, Jones SM. The Role of Social Support in Coping with Stress among African American Adolescents. J Res Adolesc. 2012;22(1):218-233.

Author’s Last name, First name. Title of Webpage. Website Name [Internet]. Publication date. [cited date]. Available from: URL.

Example : Centers for Disease Control and Prevention. COVID-19: How to Protect Yourself and Others [Internet]. 2020 Dec 11. [cited 2023 Apr 1]. Available from: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. Title of Article. Title of Magazine. Year of publication; month and day of publication:page numbers.

Example : Smith M. The Power of Positive Thinking. Psychology Today. 2019 Mar 1:32-35.

Author’s Last name, First name. Title of Article. Title of Newspaper. Year of publication; month and day of publication:page numbers.

Example : Johnson B. New Study Shows Benefits of Exercise on Mental Health. The New York Times. 2021 Feb 15:A4.

Editor’s Last name, First name, editor. Title of Book. Edition number. Place of publication: Publisher; Year of publication.

Example: Thompson JP, editor. Social Work in the 21st Century. 1st ed. Thousand Oaks, CA: Sage Publications; 2014.

Author’s Last name, First name. Title of Chapter. In: Editor’s Last name, First name, editor. Title of Book. Edition number. Place of publication: Publisher; Year of publication. page numbers.

Example : Johnson KS. The Future of Social Work: Challenges and Opportunities. In: Thompson JP, editor. Social Work in the 21st Century. 1st ed. Thousand Oaks, CA: Sage Publications; 2014. p. 105-118.

Turabian Style

Turabian style is a variation of the Chicago style used in academic writing, particularly in the fields of history and humanities. Here are the different reference formats in Turabian style:

Author’s Last name, First name. Title of Book. Place of publication: Publisher, Year of publication.

Example : Smith, John K. The Psychology of Social Interaction. Oxford: Wiley-Blackwell, 2005.

Author’s Last name, First name. “Title of Article.” Title of Journal volume number, no. issue number (Year of publication): page numbers.

Example : Brown, LM, Keating, JG, Jones, SM. “The Role of Social Support in Coping with Stress among African American Adolescents.” J Res Adolesc 22, no. 1 (2012): 218-233.

Author’s Last name, First name. “Title of Webpage.” Name of Website. Publication date. Accessed date. URL.

Example : Centers for Disease Control and Prevention. “COVID-19: How to Protect Yourself and Others.” CDC. December 11, 2020. Accessed April 1, 2023. https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html.

Author’s Last name, First name. “Title of Article.” Title of Magazine, Month Day, Year of publication, page numbers.

Example : Smith, M. “The Power of Positive Thinking.” Psychology Today, March 1, 2019, 32-35.

Author’s Last name, First name. “Title of Article.” Title of Newspaper, Month Day, Year of publication.

Example : Johnson, B. “New Study Shows Benefits of Exercise on Mental Health.” The New York Times, February 15, 2021.

Editor’s Last name, First name, ed. Title of Book. Place of publication: Publisher, Year of publication.

Example : Thompson, JP, ed. Social Work in the 21st Century. Thousand Oaks, CA: Sage Publications, 2014.

Author’s Last name, First name. “Title of Chapter.” In Title of Book, edited by Editor’s Last name, First name, page numbers. Place of publication: Publisher, Year of publication.

Example : Johnson, KS. “The Future of Social Work: Challenges and Opportunities.” In Social Work in the 21st Century, edited by Thompson, JP, 105-118. Thousand Oaks, CA: Sage Publications, 2014.

IEEE (Institute of Electrical and Electronics Engineers) Style

IEEE (Institute of Electrical and Electronics Engineers) style is commonly used in engineering, computer science, and other technical fields. Here are the different reference formats in IEEE style:

Author’s Last name, First name. Book Title. Place of Publication: Publisher, Year of publication.

Example : Oppenheim, A. V., & Schafer, R. W. Discrete-Time Signal Processing. Upper Saddle River, NJ: Prentice Hall, 2010.

Author’s Last name, First name. “Title of Article.” Abbreviated Journal Title, vol. number, no. issue number, pp. page numbers, Month year of publication.

Example: Shannon, C. E. “A Mathematical Theory of Communication.” Bell System Technical Journal, vol. 27, no. 3, pp. 379-423, July 1948.

Conference paper

Author’s Last name, First name. “Title of Paper.” In Title of Conference Proceedings, Place of Conference, Date of Conference, pp. page numbers, Year of publication.

Example: Gupta, S., & Kumar, P. “An Improved System of Linear Discriminant Analysis for Face Recognition.” In Proceedings of the 2011 International Conference on Computer Science and Network Technology, Harbin, China, Dec. 2011, pp. 144-147.

Author’s Last name, First name. “Title of Webpage.” Name of Website. Date of publication or last update. Accessed date. URL.

Example : National Aeronautics and Space Administration. “Apollo 11.” NASA. July 20, 1969. Accessed April 1, 2023. https://www.nasa.gov/mission_pages/apollo/apollo11.html.

Technical report

Author’s Last name, First name. “Title of Report.” Name of Institution or Organization, Report number, Year of publication.

Example : Smith, J. R. “Development of a New Solar Panel Technology.” National Renewable Energy Laboratory, NREL/TP-6A20-51645, 2011.

Author’s Last name, First name. “Title of Patent.” Patent number, Issue date.

Example : Suzuki, H. “Method of Producing Carbon Nanotubes.” US Patent 7,151,019, December 19, 2006.

Standard Title. Standard number, Publication date.

Example : IEEE Standard for Floating-Point Arithmetic. IEEE Std 754-2008, August 29, 2008

ACS (American Chemical Society) Style

ACS (American Chemical Society) style is commonly used in chemistry and related fields. Here are the different reference formats in ACS style:

Author’s Last name, First name; Author’s Last name, First name. Title of Article. Abbreviated Journal Title Year, Volume, Page Numbers.

Example : Wang, Y.; Zhao, X.; Cui, Y.; Ma, Y. Facile Preparation of Fe3O4/graphene Composites Using a Hydrothermal Method for High-Performance Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2012, 4, 2715-2721.

Author’s Last name, First name. Book Title; Publisher: Place of Publication, Year of Publication.

Example : Carey, F. A. Organic Chemistry; McGraw-Hill: New York, 2008.

Author’s Last name, First name. Chapter Title. In Book Title; Editor’s Last name, First name, Ed.; Publisher: Place of Publication, Year of Publication; Volume number, Chapter number, Page Numbers.

Example : Grossman, R. B. Analytical Chemistry of Aerosols. In Aerosol Measurement: Principles, Techniques, and Applications; Baron, P. A.; Willeke, K., Eds.; Wiley-Interscience: New York, 2001; Chapter 10, pp 395-424.

Author’s Last name, First name. Title of Webpage. Website Name, URL (accessed date).

Example : National Institute of Standards and Technology. Atomic Spectra Database. https://www.nist.gov/pml/atomic-spectra-database (accessed April 1, 2023).

Author’s Last name, First name. Patent Number. Patent Date.

Example : Liu, Y.; Huang, H.; Chen, H.; Zhang, W. US Patent 9,999,999, December 31, 2022.

Author’s Last name, First name; Author’s Last name, First name. Title of Article. In Title of Conference Proceedings, Publisher: Place of Publication, Year of Publication; Volume Number, Page Numbers.

Example : Jia, H.; Xu, S.; Wu, Y.; Wu, Z.; Tang, Y.; Huang, X. Fast Adsorption of Organic Pollutants by Graphene Oxide. In Proceedings of the 15th International Conference on Environmental Science and Technology, American Chemical Society: Washington, DC, 2017; Volume 1, pp 223-228.

AMA (American Medical Association) Style

AMA (American Medical Association) style is commonly used in medical and scientific fields. Here are the different reference formats in AMA style:

Author’s Last name, First name. Article Title. Journal Abbreviation. Year; Volume(Issue):Page Numbers.

Example : Jones, R. A.; Smith, B. C. The Role of Vitamin D in Maintaining Bone Health. JAMA. 2019;321(17):1765-1773.

Author’s Last name, First name. Book Title. Edition number. Place of Publication: Publisher; Year.

Example : Guyton, A. C.; Hall, J. E. Textbook of Medical Physiology. 13th ed. Philadelphia, PA: Saunders; 2015.

Author’s Last name, First name. Chapter Title. In: Editor’s Last name, First name, ed. Book Title. Edition number. Place of Publication: Publisher; Year: Page Numbers.

Example: Rajakumar, K. Vitamin D and Bone Health. In: Holick, M. F., ed. Vitamin D: Physiology, Molecular Biology, and Clinical Applications. 2nd ed. New York, NY: Springer; 2010:211-222.

Author’s Last name, First name. Webpage Title. Website Name. URL. Published date. Updated date. Accessed date.

Example : National Cancer Institute. Breast Cancer Prevention (PDQ®)–Patient Version. National Cancer Institute. https://www.cancer.gov/types/breast/patient/breast-prevention-pdq. Published October 11, 2022. Accessed April 1, 2023.

Author’s Last name, First name. Conference presentation title. In: Conference Title; Conference Date; Place of Conference.

Example : Smith, J. R. Vitamin D and Bone Health: A Meta-Analysis. In: Proceedings of the Annual Meeting of the American Society for Bone and Mineral Research; September 20-23, 2022; San Diego, CA.

Thesis or dissertation

Author’s Last name, First name. Title of Thesis or Dissertation. Degree level [Doctoral dissertation or Master’s thesis]. University Name; Year.

Example : Wilson, S. A. The Effects of Vitamin D Supplementation on Bone Health in Postmenopausal Women [Doctoral dissertation]. University of California, Los Angeles; 2018.

ASCE (American Society of Civil Engineers) Style

The ASCE (American Society of Civil Engineers) style is commonly used in civil engineering fields. Here are the different reference formats in ASCE style:

Author’s Last name, First name. “Article Title.” Journal Title, volume number, issue number (year): page numbers. DOI or URL (if available).

Example : Smith, J. R. “Evaluation of the Effectiveness of Sustainable Drainage Systems in Urban Areas.” Journal of Environmental Engineering, vol. 146, no. 3 (2020): 04020010. https://doi.org/10.1061/(ASCE)EE.1943-7870.0001668.

Example : McCuen, R. H. Hydrologic Analysis and Design. 4th ed. Upper Saddle River, NJ: Pearson Education; 2013.

Author’s Last name, First name. “Chapter Title.” In: Editor’s Last name, First name, ed. Book Title. Edition number. Place of Publication: Publisher; Year: page numbers.

Example : Maidment, D. R. “Floodplain Management in the United States.” In: Shroder, J. F., ed. Treatise on Geomorphology. San Diego, CA: Academic Press; 2013: 447-460.

Author’s Last name, First name. “Paper Title.” In: Conference Title; Conference Date; Location. Place of Publication: Publisher; Year: page numbers.

Example: Smith, J. R. “Sustainable Drainage Systems for Urban Areas.” In: Proceedings of the ASCE International Conference on Sustainable Infrastructure; November 6-9, 2019; Los Angeles, CA. Reston, VA: American Society of Civil Engineers; 2019: 156-163.

Author’s Last name, First name. “Report Title.” Report number. Place of Publication: Publisher; Year.

Example : U.S. Army Corps of Engineers. “Hurricane Sandy Coastal Risk Reduction Program, New York and New Jersey.” Report No. P-15-001. Washington, DC: U.S. Army Corps of Engineers; 2015.

CSE (Council of Science Editors) Style

The CSE (Council of Science Editors) style is commonly used in the scientific and medical fields. Here are the different reference formats in CSE style:

Author’s Last name, First Initial. Middle Initial. “Article Title.” Journal Title. Year;Volume(Issue):Page numbers.

Example : Smith, J.R. “Evaluation of the Effectiveness of Sustainable Drainage Systems in Urban Areas.” Journal of Environmental Engineering. 2020;146(3):04020010.

Author’s Last name, First Initial. Middle Initial. Book Title. Edition number. Place of Publication: Publisher; Year.

Author’s Last name, First Initial. Middle Initial. “Chapter Title.” In: Editor’s Last name, First Initial. Middle Initial., ed. Book Title. Edition number. Place of Publication: Publisher; Year:Page numbers.

Author’s Last name, First Initial. Middle Initial. “Paper Title.” In: Conference Title; Conference Date; Location. Place of Publication: Publisher; Year.

Example : Smith, J.R. “Sustainable Drainage Systems for Urban Areas.” In: Proceedings of the ASCE International Conference on Sustainable Infrastructure; November 6-9, 2019; Los Angeles, CA. Reston, VA: American Society of Civil Engineers; 2019.

Author’s Last name, First Initial. Middle Initial. “Report Title.” Report number. Place of Publication: Publisher; Year.

Bluebook Style

The Bluebook style is commonly used in the legal field for citing legal documents and sources. Here are the different reference formats in Bluebook style:

Case citation

Case name, volume source page (Court year).

Example : Brown v. Board of Education, 347 U.S. 483 (1954).

Statute citation

Name of Act, volume source § section number (year).

Example : Clean Air Act, 42 U.S.C. § 7401 (1963).

Regulation citation

Name of regulation, volume source § section number (year).

Example: Clean Air Act, 40 C.F.R. § 52.01 (2019).

Book citation

Author’s Last name, First Initial. Middle Initial. Book Title. Edition number (if applicable). Place of Publication: Publisher; Year.

Example: Smith, J.R. Legal Writing and Analysis. 3rd ed. New York, NY: Aspen Publishers; 2015.

Journal article citation

Author’s Last name, First Initial. Middle Initial. “Article Title.” Journal Title. Volume number (year): first page-last page.

Example: Garcia, C. “The Right to Counsel: An International Comparison.” International Journal of Legal Information. 43 (2015): 63-94.

Website citation

Author’s Last name, First Initial. Middle Initial. “Page Title.” Website Title. URL (accessed month day, year).

Example : United Nations. “Universal Declaration of Human Rights.” United Nations. https://www.un.org/en/universal-declaration-human-rights/ (accessed January 3, 2023).

Oxford Style

The Oxford style, also known as the Oxford referencing system or the documentary-note citation system, is commonly used in the humanities, including literature, history, and philosophy. Here are the different reference formats in Oxford style:

Author’s Last name, First name. Book Title. Place of Publication: Publisher, Year of Publication.

Example : Smith, John. The Art of Writing. New York: Penguin, 2020.

Author’s Last name, First name. “Article Title.” Journal Title volume, no. issue (year): page range.

Example: Garcia, Carlos. “The Role of Ethics in Philosophy.” Philosophy Today 67, no. 3 (2019): 53-68.

Chapter in an edited book citation

Author’s Last name, First name. “Chapter Title.” In Book Title, edited by Editor’s Name, page range. Place of Publication: Publisher, Year of Publication.

Example : Lee, Mary. “Feminism in the 21st Century.” In The Oxford Handbook of Feminism, edited by Jane Smith, 51-69. Oxford: Oxford University Press, 2018.

Author’s Last name, First name. “Page Title.” Website Title. URL (accessed day month year).

Example : Jones, David. “The Importance of Learning Languages.” Oxford Language Center. https://www.oxfordlanguagecenter.com/importance-of-learning-languages/ (accessed 3 January 2023).

Dissertation or thesis citation

Author’s Last name, First name. “Title of Dissertation/Thesis.” PhD diss., University Name, Year of Publication.

Example : Brown, Susan. “The Art of Storytelling in American Literature.” PhD diss., University of Oxford, 2020.

Newspaper article citation

Author’s Last name, First name. “Article Title.” Newspaper Title, Month Day, Year.

Example : Robinson, Andrew. “New Developments in Climate Change Research.” The Guardian, September 15, 2022.

AAA (American Anthropological Association) Style

The American Anthropological Association (AAA) style is commonly used in anthropology research papers and journals. Here are the different reference formats in AAA style:

Author’s Last name, First name. Year of Publication. Book Title. Place of Publication: Publisher.

Example : Smith, John. 2019. The Anthropology of Food. New York: Routledge.

Author’s Last name, First name. Year of Publication. “Article Title.” Journal Title volume, no. issue: page range.

Example : Garcia, Carlos. 2021. “The Role of Ethics in Anthropology.” American Anthropologist 123, no. 2: 237-251.

Author’s Last name, First name. Year of Publication. “Chapter Title.” In Book Title, edited by Editor’s Name, page range. Place of Publication: Publisher.

Example: Lee, Mary. 2018. “Feminism in Anthropology.” In The Oxford Handbook of Feminism, edited by Jane Smith, 51-69. Oxford: Oxford University Press.

Author’s Last name, First name. Year of Publication. “Page Title.” Website Title. URL (accessed day month year).

Example : Jones, David. 2020. “The Importance of Learning Languages.” Oxford Language Center. https://www.oxfordlanguagecenter.com/importance-of-learning-languages/ (accessed January 3, 2023).

Author’s Last name, First name. Year of Publication. “Title of Dissertation/Thesis.” PhD diss., University Name.

Example : Brown, Susan. 2022. “The Art of Storytelling in Anthropology.” PhD diss., University of California, Berkeley.

Author’s Last name, First name. Year of Publication. “Article Title.” Newspaper Title, Month Day.

Example : Robinson, Andrew. 2021. “New Developments in Anthropology Research.” The Guardian, September 15.

AIP (American Institute of Physics) Style

The American Institute of Physics (AIP) style is commonly used in physics research papers and journals. Here are the different reference formats in AIP style:

Example : Johnson, S. D. 2021. “Quantum Computing and Information.” Journal of Applied Physics 129, no. 4: 043102.

Example : Feynman, Richard. 2018. The Feynman Lectures on Physics. New York: Basic Books.

Example : Jones, David. 2020. “The Future of Quantum Computing.” In The Handbook of Physics, edited by John Smith, 125-136. Oxford: Oxford University Press.

Conference proceedings citation

Author’s Last name, First name. Year of Publication. “Title of Paper.” Proceedings of Conference Name, date and location: page range. Place of Publication: Publisher.

Example : Chen, Wei. 2019. “The Applications of Nanotechnology in Solar Cells.” Proceedings of the 8th International Conference on Nanotechnology, July 15-17, Tokyo, Japan: 224-229. New York: AIP Publishing.

Example : American Institute of Physics. 2022. “About AIP Publishing.” AIP Publishing. https://publishing.aip.org/about-aip-publishing/ (accessed January 3, 2023).

Patent citation

Author’s Last name, First name. Year of Publication. Patent Number.

Example : Smith, John. 2018. US Patent 9,873,644.

References Writing Guide

Here are some general guidelines for writing references:

• Follow the citation style guidelines: Different disciplines and journals may require different citation styles (e.g., APA, MLA, Chicago). It is important to follow the specific guidelines for the citation style required.
• Include all necessary information : Each citation should include enough information for readers to locate the source. For example, a journal article citation should include the author(s), title of the article, journal title, volume number, issue number, page numbers, and publication year.
• Use proper formatting: Citation styles typically have specific formatting requirements for different types of sources. Make sure to follow the proper formatting for each citation.
• Order citations alphabetically: If listing multiple sources, they should be listed alphabetically by the author’s last name.
• Be consistent: Use the same citation style throughout the entire paper or project.
• Check for accuracy: Double-check all citations to ensure accuracy, including correct spelling of author names and publication information.
• Use reputable sources: When selecting sources to cite, choose reputable and authoritative sources. Avoid sources that are biased or unreliable.
• Include all sources: Make sure to include all sources used in the research, including those that were not directly quoted but still informed the work.
• Use online tools : There are online tools available (e.g., citation generators) that can help with formatting and organizing references.

Purpose of References in Research

References in research serve several purposes:

• To give credit to the original authors or sources of information used in the research. It is important to acknowledge the work of others and avoid plagiarism.
• To provide evidence for the claims made in the research. References can support the arguments, hypotheses, or conclusions presented in the research by citing relevant studies, data, or theories.
• To allow readers to find and verify the sources used in the research. References provide the necessary information for readers to locate and access the sources cited in the research, which allows them to evaluate the quality and reliability of the information presented.
• To situate the research within the broader context of the field. References can show how the research builds on or contributes to the existing body of knowledge, and can help readers to identify gaps in the literature that the research seeks to address.

Importance of References in Research

References play an important role in research for several reasons:

• Credibility : By citing authoritative sources, references lend credibility to the research and its claims. They provide evidence that the research is based on a sound foundation of knowledge and has been carefully researched.
• Avoidance of Plagiarism : References help researchers avoid plagiarism by giving credit to the original authors or sources of information. This is important for ethical reasons and also to avoid legal repercussions.
• Reproducibility : References allow others to reproduce the research by providing detailed information on the sources used. This is important for verification of the research and for others to build on the work.
• Context : References provide context for the research by situating it within the broader body of knowledge in the field. They help researchers to understand where their work fits in and how it builds on or contributes to existing knowledge.
• Evaluation : References provide a means for others to evaluate the research by allowing them to assess the quality and reliability of the sources used.

Advantages of References in Research

There are several advantages of including references in research:

• Acknowledgment of Sources: Including references gives credit to the authors or sources of information used in the research. This is important to acknowledge the original work and avoid plagiarism.
• Evidence and Support : References can provide evidence to support the arguments, hypotheses, or conclusions presented in the research. This can add credibility and strength to the research.
• Reproducibility : References provide the necessary information for others to reproduce the research. This is important for the verification of the research and for others to build on the work.
• Context : References can help to situate the research within the broader body of knowledge in the field. This helps researchers to understand where their work fits in and how it builds on or contributes to existing knowledge.
• Evaluation : Including references allows others to evaluate the research by providing a means to assess the quality and reliability of the sources used.
• Ongoing Conversation: References allow researchers to engage in ongoing conversations and debates within their fields. They can show how the research builds on or contributes to the existing body of knowledge.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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Home / Guides / Citation Guides / How to Cite Sources

How to Cite Sources

Here is a complete list for how to cite sources. Most of these guides present citation guidance and examples in MLA, APA, and Chicago.

If you’re looking for general information on MLA or APA citations , the EasyBib Writing Center was designed for you! It has articles on what’s needed in an MLA in-text citation , how to format an APA paper, what an MLA annotated bibliography is, making an MLA works cited page, and much more!

MLA Format Citation Examples

The Modern Language Association created the MLA Style, currently in its 9th edition, to provide researchers with guidelines for writing and documenting scholarly borrowings.  Most often used in the humanities, MLA style (or MLA format ) has been adopted and used by numerous other disciplines, in multiple parts of the world.

MLA provides standard rules to follow so that most research papers are formatted in a similar manner. This makes it easier for readers to comprehend the information. The MLA in-text citation guidelines, MLA works cited standards, and MLA annotated bibliography instructions provide scholars with the information they need to properly cite sources in their research papers, articles, and assignments.

• Book Chapter
• Conference Paper
• Documentary
• Encyclopedia
• Google Images
• Kindle Book
• Memorial Inscription
• Museum Exhibit
• Painting or Artwork
• PowerPoint Presentation
• Sheet Music
• Thesis or Dissertation
• YouTube Video

APA Format Citation Examples

The American Psychological Association created the APA citation style in 1929 as a way to help psychologists, anthropologists, and even business managers establish one common way to cite sources and present content.

APA is used when citing sources for academic articles such as journals, and is intended to help readers better comprehend content, and to avoid language bias wherever possible. The APA style (or APA format ) is now in its 7th edition, and provides citation style guides for virtually any type of resource.

Chicago Style Citation Examples

The Chicago/Turabian style of citing sources is generally used when citing sources for humanities papers, and is best known for its requirement that writers place bibliographic citations at the bottom of a page (in Chicago-format footnotes ) or at the end of a paper (endnotes).

The Turabian and Chicago citation styles are almost identical, but the Turabian style is geared towards student published papers such as theses and dissertations, while the Chicago style provides guidelines for all types of publications. This is why you’ll commonly see Chicago style and Turabian style presented together. The Chicago Manual of Style is currently in its 17th edition, and Turabian’s A Manual for Writers of Research Papers, Theses, and Dissertations is in its 8th edition.

Citing Specific Sources or Events

• Declaration of Independence
• Gettysburg Address
• Martin Luther King Jr. Speech
• President Obama’s Farewell Address
• President Trump’s Inauguration Speech
• White House Press Briefing

Additional FAQs

• Citing Archived Contributors
• Citing a Blog
• Citing a Book Chapter
• Citing a Source in a Foreign Language
• Citing an Image
• Citing a Song
• Citing Special Contributors
• Citing a Translated Article
• Citing a Tweet

6 Interesting Citation Facts

The world of citations may seem cut and dry, but there’s more to them than just specific capitalization rules, MLA in-text citations , and other formatting specifications. Citations have been helping researches document their sources for hundreds of years, and are a great way to learn more about a particular subject area.

Ever wonder what sets all the different styles apart, or how they came to be in the first place? Read on for some interesting facts about citations!

1. There are Over 7,000 Different Citation Styles

You may be familiar with MLA and APA citation styles, but there are actually thousands of citation styles used for all different academic disciplines all across the world. Deciding which one to use can be difficult, so be sure to ask you instructor which one you should be using for your next paper.

2. Some Citation Styles are Named After People

While a majority of citation styles are named for the specific organizations that publish them (i.e. APA is published by the American Psychological Association, and MLA format is named for the Modern Language Association), some are actually named after individuals. The most well-known example of this is perhaps Turabian style, named for Kate L. Turabian, an American educator and writer. She developed this style as a condensed version of the Chicago Manual of Style in order to present a more concise set of rules to students.

3. There are Some Really Specific and Uniquely Named Citation Styles

How specific can citation styles get? The answer is very. For example, the “Flavour and Fragrance Journal” style is based on a bimonthly, peer-reviewed scientific journal published since 1985 by John Wiley & Sons. It publishes original research articles, reviews and special reports on all aspects of flavor and fragrance. Another example is “Nordic Pulp and Paper Research,” a style used by an international scientific magazine covering science and technology for the areas of wood or bio-mass constituents.

4. More citations were created on  EasyBib.com  in the first quarter of 2018 than there are people in California.

The US Census Bureau estimates that approximately 39.5 million people live in the state of California. Meanwhile, about 43 million citations were made on EasyBib from January to March of 2018. That’s a lot of citations.

5. “Citations” is a Word With a Long History

The word “citations” can be traced back literally thousands of years to the Latin word “citare” meaning “to summon, urge, call; put in sudden motion, call forward; rouse, excite.” The word then took on its more modern meaning and relevance to writing papers in the 1600s, where it became known as the “act of citing or quoting a passage from a book, etc.”

6. Citation Styles are Always Changing

The concept of citations always stays the same. It is a means of preventing plagiarism and demonstrating where you relied on outside sources. The specific style rules, however, can and do change regularly. For example, in 2018 alone, 46 new citation styles were introduced , and 106 updates were made to exiting styles. At EasyBib, we are always on the lookout for ways to improve our styles and opportunities to add new ones to our list.

Why Citations Matter

Here are the ways accurate citations can help your students achieve academic success, and how you can answer the dreaded question, “why should I cite my sources?”

They Give Credit to the Right People

Citing their sources makes sure that the reader can differentiate the student’s original thoughts from those of other researchers. Not only does this make sure that the sources they use receive proper credit for their work, it ensures that the student receives deserved recognition for their unique contributions to the topic. Whether the student is citing in MLA format , APA format , or any other style, citations serve as a natural way to place a student’s work in the broader context of the subject area, and serve as an easy way to gauge their commitment to the project.

They Provide Hard Evidence of Ideas

Having many citations from a wide variety of sources related to their idea means that the student is working on a well-researched and respected subject. Citing sources that back up their claim creates room for fact-checking and further research . And, if they can cite a few sources that have the converse opinion or idea, and then demonstrate to the reader why they believe that that viewpoint is wrong by again citing credible sources, the student is well on their way to winning over the reader and cementing their point of view.

They Promote Originality and Prevent Plagiarism

The point of research projects is not to regurgitate information that can already be found elsewhere. We have Google for that! What the student’s project should aim to do is promote an original idea or a spin on an existing idea, and use reliable sources to promote that idea. Copying or directly referencing a source without proper citation can lead to not only a poor grade, but accusations of academic dishonesty. By citing their sources regularly and accurately, students can easily avoid the trap of plagiarism , and promote further research on their topic.

They Create Better Researchers

By researching sources to back up and promote their ideas, students are becoming better researchers without even knowing it! Each time a new source is read or researched, the student is becoming more engaged with the project and is developing a deeper understanding of the subject area. Proper citations demonstrate a breadth of the student’s reading and dedication to the project itself. By creating citations, students are compelled to make connections between their sources and discern research patterns. Each time they complete this process, they are helping themselves become better researchers and writers overall.

When is the Right Time to Start Making Citations?

Make in-text/parenthetical citations as you need them.

As you are writing your paper, be sure to include references within the text that correspond with references in a works cited or bibliography. These are usually called in-text citations or parenthetical citations in MLA and APA formats. The most effective time to complete these is directly after you have made your reference to another source. For instance, after writing the line from Charles Dickens’ A Tale of Two Cities : “It was the best of times, it was the worst of times…,” you would include a citation like this (depending on your chosen citation style):

(Dickens 11).

This signals to the reader that you have referenced an outside source. What’s great about this system is that the in-text citations serve as a natural list for all of the citations you have made in your paper, which will make completing the works cited page a whole lot easier. After you are done writing, all that will be left for you to do is scan your paper for these references, and then build a works cited page that includes a citation for each one.

Need help creating an MLA works cited page ? Try the MLA format generator on EasyBib.com! We also have a guide on how to format an APA reference page .

2. Understand the General Formatting Rules of Your Citation Style Before You Start Writing

While reading up on paper formatting may not sound exciting, being aware of how your paper should look early on in the paper writing process is super important. Citation styles can dictate more than just the appearance of the citations themselves, but rather can impact the layout of your paper as a whole, with specific guidelines concerning margin width, title treatment, and even font size and spacing. Knowing how to organize your paper before you start writing will ensure that you do not receive a low grade for something as trivial as forgetting a hanging indent.

Don’t know where to start? Here’s a formatting guide on APA format .

3. Double-check All of Your Outside Sources for Relevance and Trustworthiness First

Collecting outside sources that support your research and specific topic is a critical step in writing an effective paper. But before you run to the library and grab the first 20 books you can lay your hands on, keep in mind that selecting a source to include in your paper should not be taken lightly. Before you proceed with using it to backup your ideas, run a quick Internet search for it and see if other scholars in your field have written about it as well. Check to see if there are book reviews about it or peer accolades. If you spot something that seems off to you, you may want to consider leaving it out of your work. Doing this before your start making citations can save you a ton of time in the long run.

Finished with your paper? It may be time to run it through a grammar and plagiarism checker , like the one offered by EasyBib Plus. If you’re just looking to brush up on the basics, our grammar guides  are ready anytime you are.

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13.1 Formatting a Research Paper

Learning objectives.

• Identify the major components of a research paper written using American Psychological Association (APA) style.
• Apply general APA style and formatting conventions in a research paper.

In this chapter, you will learn how to use APA style , the documentation and formatting style followed by the American Psychological Association, as well as MLA style , from the Modern Language Association. There are a few major formatting styles used in academic texts, including AMA, Chicago, and Turabian:

• AMA (American Medical Association) for medicine, health, and biological sciences
• APA (American Psychological Association) for education, psychology, and the social sciences
• Chicago—a common style used in everyday publications like magazines, newspapers, and books
• MLA (Modern Language Association) for English, literature, arts, and humanities
• Turabian—another common style designed for its universal application across all subjects and disciplines

While all the formatting and citation styles have their own use and applications, in this chapter we focus our attention on the two styles you are most likely to use in your academic studies: APA and MLA.

If you find that the rules of proper source documentation are difficult to keep straight, you are not alone. Writing a good research paper is, in and of itself, a major intellectual challenge. Having to follow detailed citation and formatting guidelines as well may seem like just one more task to add to an already-too-long list of requirements.

Following these guidelines, however, serves several important purposes. First, it signals to your readers that your paper should be taken seriously as a student’s contribution to a given academic or professional field; it is the literary equivalent of wearing a tailored suit to a job interview. Second, it shows that you respect other people’s work enough to give them proper credit for it. Finally, it helps your reader find additional materials if he or she wishes to learn more about your topic.

Furthermore, producing a letter-perfect APA-style paper need not be burdensome. Yes, it requires careful attention to detail. However, you can simplify the process if you keep these broad guidelines in mind:

• Work ahead whenever you can. Chapter 11 “Writing from Research: What Will I Learn?” includes tips for keeping track of your sources early in the research process, which will save time later on.
• Get it right the first time. Apply APA guidelines as you write, so you will not have much to correct during the editing stage. Again, putting in a little extra time early on can save time later.
• Use the resources available to you. In addition to the guidelines provided in this chapter, you may wish to consult the APA website at http://www.apa.org or the Purdue University Online Writing lab at http://owl.english.purdue.edu , which regularly updates its online style guidelines.

General Formatting Guidelines

This chapter provides detailed guidelines for using the citation and formatting conventions developed by the American Psychological Association, or APA. Writers in disciplines as diverse as astrophysics, biology, psychology, and education follow APA style. The major components of a paper written in APA style are listed in the following box.

These are the major components of an APA-style paper:

Body, which includes the following:

• Headings and, if necessary, subheadings to organize the content
• In-text citations of research sources
• References page

All these components must be saved in one document, not as separate documents.

The title page of your paper includes the following information:

• Title of the paper
• Author’s name
• Name of the institution with which the author is affiliated
• Header at the top of the page with the paper title (in capital letters) and the page number (If the title is lengthy, you may use a shortened form of it in the header.)

List the first three elements in the order given in the previous list, centered about one third of the way down from the top of the page. Use the headers and footers tool of your word-processing program to add the header, with the title text at the left and the page number in the upper-right corner. Your title page should look like the following example.

The next page of your paper provides an abstract , or brief summary of your findings. An abstract does not need to be provided in every paper, but an abstract should be used in papers that include a hypothesis. A good abstract is concise—about one hundred fifty to two hundred fifty words—and is written in an objective, impersonal style. Your writing voice will not be as apparent here as in the body of your paper. When writing the abstract, take a just-the-facts approach, and summarize your research question and your findings in a few sentences.

In Chapter 12 “Writing a Research Paper” , you read a paper written by a student named Jorge, who researched the effectiveness of low-carbohydrate diets. Read Jorge’s abstract. Note how it sums up the major ideas in his paper without going into excessive detail.

Write an abstract summarizing your paper. Briefly introduce the topic, state your findings, and sum up what conclusions you can draw from your research. Use the word count feature of your word-processing program to make sure your abstract does not exceed one hundred fifty words.

Depending on your field of study, you may sometimes write research papers that present extensive primary research, such as your own experiment or survey. In your abstract, summarize your research question and your findings, and briefly indicate how your study relates to prior research in the field.

Margins, Pagination, and Headings

APA style requirements also address specific formatting concerns, such as margins, pagination, and heading styles, within the body of the paper. Review the following APA guidelines.

Use these general guidelines to format the paper:

• Set the top, bottom, and side margins of your paper at 1 inch.
• Use double-spaced text throughout your paper.
• Use a standard font, such as Times New Roman or Arial, in a legible size (10- to 12-point).
• Use continuous pagination throughout the paper, including the title page and the references section. Page numbers appear flush right within your header.
• Section headings and subsection headings within the body of your paper use different types of formatting depending on the level of information you are presenting. Additional details from Jorge’s paper are provided.

Begin formatting the final draft of your paper according to APA guidelines. You may work with an existing document or set up a new document if you choose. Include the following:

• Your title page
• The abstract you created in Note 13.8 “Exercise 1”
• Correct headers and page numbers for your title page and abstract

APA style uses section headings to organize information, making it easy for the reader to follow the writer’s train of thought and to know immediately what major topics are covered. Depending on the length and complexity of the paper, its major sections may also be divided into subsections, sub-subsections, and so on. These smaller sections, in turn, use different heading styles to indicate different levels of information. In essence, you are using headings to create a hierarchy of information.

The following heading styles used in APA formatting are listed in order of greatest to least importance:

• Section headings use centered, boldface type. Headings use title case, with important words in the heading capitalized.
• Subsection headings use left-aligned, boldface type. Headings use title case.
• The third level uses left-aligned, indented, boldface type. Headings use a capital letter only for the first word, and they end in a period.
• The fourth level follows the same style used for the previous level, but the headings are boldfaced and italicized.
• The fifth level follows the same style used for the previous level, but the headings are italicized and not boldfaced.

Visually, the hierarchy of information is organized as indicated in Table 13.1 “Section Headings” .

Table 13.1 Section Headings

A college research paper may not use all the heading levels shown in Table 13.1 “Section Headings” , but you are likely to encounter them in academic journal articles that use APA style. For a brief paper, you may find that level 1 headings suffice. Longer or more complex papers may need level 2 headings or other lower-level headings to organize information clearly. Use your outline to craft your major section headings and determine whether any subtopics are substantial enough to require additional levels of headings.

Working with the document you developed in Note 13.11 “Exercise 2” , begin setting up the heading structure of the final draft of your research paper according to APA guidelines. Include your title and at least two to three major section headings, and follow the formatting guidelines provided above. If your major sections should be broken into subsections, add those headings as well. Use your outline to help you.

Because Jorge used only level 1 headings, his Exercise 3 would look like the following:

Citation Guidelines

In-text citations.

Throughout the body of your paper, include a citation whenever you quote or paraphrase material from your research sources. As you learned in Chapter 11 “Writing from Research: What Will I Learn?” , the purpose of citations is twofold: to give credit to others for their ideas and to allow your reader to follow up and learn more about the topic if desired. Your in-text citations provide basic information about your source; each source you cite will have a longer entry in the references section that provides more detailed information.

In-text citations must provide the name of the author or authors and the year the source was published. (When a given source does not list an individual author, you may provide the source title or the name of the organization that published the material instead.) When directly quoting a source, it is also required that you include the page number where the quote appears in your citation.

This information may be included within the sentence or in a parenthetical reference at the end of the sentence, as in these examples.

Epstein (2010) points out that “junk food cannot be considered addictive in the same way that we think of psychoactive drugs as addictive” (p. 137).

Here, the writer names the source author when introducing the quote and provides the publication date in parentheses after the author’s name. The page number appears in parentheses after the closing quotation marks and before the period that ends the sentence.

Addiction researchers caution that “junk food cannot be considered addictive in the same way that we think of psychoactive drugs as addictive” (Epstein, 2010, p. 137).

Here, the writer provides a parenthetical citation at the end of the sentence that includes the author’s name, the year of publication, and the page number separated by commas. Again, the parenthetical citation is placed after the closing quotation marks and before the period at the end of the sentence.

As noted in the book Junk Food, Junk Science (Epstein, 2010, p. 137), “junk food cannot be considered addictive in the same way that we think of psychoactive drugs as addictive.”

Here, the writer chose to mention the source title in the sentence (an optional piece of information to include) and followed the title with a parenthetical citation. Note that the parenthetical citation is placed before the comma that signals the end of the introductory phrase.

David Epstein’s book Junk Food, Junk Science (2010) pointed out that “junk food cannot be considered addictive in the same way that we think of psychoactive drugs as addictive” (p. 137).

Another variation is to introduce the author and the source title in your sentence and include the publication date and page number in parentheses within the sentence or at the end of the sentence. As long as you have included the essential information, you can choose the option that works best for that particular sentence and source.

Citing a book with a single author is usually a straightforward task. Of course, your research may require that you cite many other types of sources, such as books or articles with more than one author or sources with no individual author listed. You may also need to cite sources available in both print and online and nonprint sources, such as websites and personal interviews. Chapter 13 “APA and MLA Documentation and Formatting” , Section 13.2 “Citing and Referencing Techniques” and Section 13.3 “Creating a References Section” provide extensive guidelines for citing a variety of source types.

Writing at Work

APA is just one of several different styles with its own guidelines for documentation, formatting, and language usage. Depending on your field of interest, you may be exposed to additional styles, such as the following:

• MLA style. Determined by the Modern Languages Association and used for papers in literature, languages, and other disciplines in the humanities.
• Chicago style. Outlined in the Chicago Manual of Style and sometimes used for papers in the humanities and the sciences; many professional organizations use this style for publications as well.
• Associated Press (AP) style. Used by professional journalists.

References List

The brief citations included in the body of your paper correspond to the more detailed citations provided at the end of the paper in the references section. In-text citations provide basic information—the author’s name, the publication date, and the page number if necessary—while the references section provides more extensive bibliographical information. Again, this information allows your reader to follow up on the sources you cited and do additional reading about the topic if desired.

The specific format of entries in the list of references varies slightly for different source types, but the entries generally include the following information:

• The name(s) of the author(s) or institution that wrote the source
• The year of publication and, where applicable, the exact date of publication
• The full title of the source
• For books, the city of publication
• For articles or essays, the name of the periodical or book in which the article or essay appears
• For magazine and journal articles, the volume number, issue number, and pages where the article appears
• For sources on the web, the URL where the source is located

The references page is double spaced and lists entries in alphabetical order by the author’s last name. If an entry continues for more than one line, the second line and each subsequent line are indented five spaces. Review the following example. ( Chapter 13 “APA and MLA Documentation and Formatting” , Section 13.3 “Creating a References Section” provides extensive guidelines for formatting reference entries for different types of sources.)

In APA style, book and article titles are formatted in sentence case, not title case. Sentence case means that only the first word is capitalized, along with any proper nouns.

Key Takeaways

• Following proper citation and formatting guidelines helps writers ensure that their work will be taken seriously, give proper credit to other authors for their work, and provide valuable information to readers.
• Working ahead and taking care to cite sources correctly the first time are ways writers can save time during the editing stage of writing a research paper.
• APA papers usually include an abstract that concisely summarizes the paper.
• APA papers use a specific headings structure to provide a clear hierarchy of information.
• In APA papers, in-text citations usually include the name(s) of the author(s) and the year of publication.
• In-text citations correspond to entries in the references section, which provide detailed bibliographical information about a source.

Writing for Success Copyright © 2015 by University of Minnesota is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

• Manuscript Preparation

How to write your references quickly and easily

• 3 minute read

Table of Contents

Every scientific paper builds on previous research – even if it’s in a new field, related studies will have preceded and informed it. In peer-reviewed articles, authors must give credit to this previous research, through citations and references. Not only does this show clearly where the current research came from, but it also helps readers understand the content of the paper better.

There is no optimum number of references for an academic article but depending on the subject you could be dealing with more than 100 different papers, conference reports, video articles, medical guidelines or any number of other resources.

That’s a lot of content to manage. Before submitting your manuscript, this needs to be checked, cross-references in the text and the list, organized and formatted.

The exact content and format of the citations and references in your paper will depend on the journal you aim to publish in, so the first step is to check the journal’s Guide for Authors before you submit.

There are two main points to pay attention to – consistency and accuracy. When you go through your manuscript to edit or proofread it, look closely at the citations within the text. Are they all the same? For example, if the journal prefers the citations to be in the format (name, year), make sure they’re all the same: (Smith, 2016).

Your citations must also be accurate and complete. Do they match your references list? Each citation should be included in the list, so cross-checking is important. It’s also common for journals to prefer that most, if not all, of the articles listed in your references be cited within the text – after all, these should be studies that contributed to the knowledge underpinning your work, not just your bedtime reading. So go through them carefully, noting any missing references or citations and filling the gaps.

Each journal has its own requirements when it comes to the content and format of references, as well as where and how you should include them in your submission, so double-check before you hit send!

In general, a reference will include authors’ names and initials, the title of the article, name of the journal, volume and issue, date, page numbers and DOI. On ScienceDirect, articles are linked to their original source (if also published on ScienceDirect) or to their Scopus record, so including the DOI can help link to the correct article.

A spotless reference list

Luckily, compiling and editing the references in your scientific manuscript can be easy – and it no longer has to be manual. Management tools like Mendeley can keep track of all your references, letting you share them with your collaborators. With the Word plugin, it’s possible to select the right citation style for the journal you’re submitting to and the tool will format your references automatically.

Like with any other part of your manuscript, it’s important to make sure your reference list has been checked and edited. Elsevier Author Services Language Editing can help, with professional manuscript editing that will help make sure your references don’t hold you back from publication.

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How to Choose a Journal to Submit an Article

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• Published: 28 May 2024

Gut microbiome remodeling and metabolomic profile improves in response to protein pacing with intermittent fasting versus continuous caloric restriction

• Alex E. Mohr   ORCID: orcid.org/0000-0001-5401-3702 1 , 2 ,
• Karen L. Sweazea 1 , 2 , 3 ,
• Devin A. Bowes   ORCID: orcid.org/0000-0001-9819-2503 2 ,
• Paniz Jasbi 4 , 5 ,
• Corrie M. Whisner   ORCID: orcid.org/0000-0003-3888-6348 1 , 2 ,
• Dorothy D. Sears   ORCID: orcid.org/0000-0002-9260-3540 1 ,
• Rosa Krajmalnik-Brown   ORCID: orcid.org/0000-0001-6064-3524 2 ,
• Yan Jin 6 ,
• Haiwei Gu 1 , 6 ,
• Judith Klein-Seetharaman   ORCID: orcid.org/0000-0002-4892-6828 1 , 4 ,
• Karen M. Arciero 7 ,
• Eric Gumpricht 8 &
• Paul J. Arciero   ORCID: orcid.org/0000-0001-7445-6164 7 , 9  

Nature Communications volume  15 , Article number:  4155 ( 2024 ) Cite this article

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• Metabolomics
• Risk factors

The gut microbiome (GM) modulates body weight/composition and gastrointestinal functioning; therefore, approaches targeting resident gut microbes have attracted considerable interest. Intermittent fasting (IF) and protein pacing (P) regimens are effective in facilitating weight loss (WL) and enhancing body composition. However, the interrelationships between IF- and P-induced WL and the GM are unknown. The current randomized controlled study describes distinct fecal microbial and plasma metabolomic signatures between combined IF-P ( n  = 21) versus a heart-healthy, calorie-restricted (CR, n  = 20) diet matched for overall energy intake in free-living human participants (women = 27; men = 14) with overweight/obesity for 8 weeks. Gut symptomatology improves and abundance of Christensenellaceae microbes and circulating cytokines and amino acid metabolites favoring fat oxidation increase with IF-P (p < 0.05), whereas metabolites associated with a longevity-related metabolic pathway increase with CR (p < 0.05). Differences indicate GM and metabolomic factors play a role in WL maintenance and body composition. This novel work provides insight into the GM and metabolomic profile of participants following an IF-P or CR diet and highlights important differences in microbial assembly associated with WL and body composition responsiveness. These data may inform future GM-focused precision nutrition recommendations using larger sample sizes of longer duration. Trial registration, March 6, 2020 (ClinicalTrials.gov as NCT04327141), based on a previous randomized intervention trial.

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Introduction.

As a principal modulator of the gut microbiome (GM) and weight status, nutritional input holds great therapeutic promise for addressing a wide range of metabolic dysregulation 1 . Dependent on the host for nutrients and fluid, one of the main processes by which the GM affects host physiology is producing bioactive metabolites from the gastrointestinal (GI) contents. Nutrient composition, feeding frequency, and meal timing impact this dependency 2 , 3 . To maintain a stable community and ecosystem, the GM must regulate its growth rate and diversity in response to nutrient availability and population density 4 . Such maintenance is affected by caloric restriction (CR) coupled with periods of feeding and intermittent fasting (IF) 5 . Moreover, we’ve recently shown the nutritional composition and meal frequency during these periods alter the metabolizable energy for the host 6 . The current study incorporates protein pacing (P), defined as four meals/day consumed evenly spaced every 4 h, consisting of 25–50 g of protein/meal 7 , 8 , 9 . Indeed, we have previously characterized a dietary approach of calorie-restricted IF-P combined and P alone 7 , 8 . These studies included nutrient-dense meal replacement shakes, along with whole foods, to quantitatively examine beneficial changes in body composition and cardiometabolic, inflammatory, and toxin-related outcomes in healthy and overweight individuals 7 , 8 , 10 , 11 , 12 . Further, recent preclinical work in mice has identified dietary protein as having anti-obesity effects after CR that are partially modulated through the GM 13 . Thus, the need to examine this in humans is warranted.

In this current work, we compare the effects of two low-calorie dietary interventions matched for weekly energy intake and expenditure; continuous caloric restriction on a heart-healthy diet (CR) aligned with current United States (US) dietary recommendations 14 versus our calorie-restricted IF-P diet 8 , 15 , in forty-one individuals with overweight or obesity, over an 8-week intervention. We hypothesize an IF-P diet may favorably influence the GM and metabolome to a greater extent than a calorie-matched CR alone. This exploratory investigation utilizes data and samples from a randomized controlled trial (NCT04327141) that compares the effects of the CR versus IF-P diet on anthropometric and cardiometabolic outcomes, as previously published 15 . As an additional analysis, we select “high” and “low” responders based on relative weight loss (WL) for a subgroup examination of the IF-P diet to better elucidate potential differential responses to intermittent fasting and protein pacing. Of special note, one individual lost 15% of their initial body weight over the 8-week intervention; this individual is followed longitudinally for a year to explore the dynamics of their GM and fecal metabolome. Novel findings from the current study shows an IF-P regimen results in improved gut symptomatology, a more pronounced community shift, and greater divergence of the gut microbiome, including microbial families and genera, such as Christensenellaceae , Rikenellaceae , and Marvinbryantia , associated with favorable metabolic profiles, compared to CR. Furthermore, IF-P significantly increases cytokines linked to lipolysis, weight loss, inflammation, and immune response. These findings shed light on the differential effects of IF-P as a promising dietary intervention for obesity management and microbiotic and metabolic health.

Intermittent fasting - protein pacing (IF-P) significantly influences gut microbiome (GM) dynamics compared to calorie restriction (CR)

We compared an IF-P vs. a CR per-protocol dietary intervention (matched for total energy intake and expenditure) over eight weeks to compare changes in weight, cardiometabolic outcomes, and the GM in men and women with overweight/obesity (IF-P: n  = 21; CR: n  = 20). One participant in each group were lost to follow-up due to non-compliance with dietary intervention (Fig.  1a ; CONSORT flow diagram: Supplementary Fig.  S1a ). The primary outcomes of dietary intake, body weight and composition responses, cardiometabolic outcomes, and hunger ratings after both dietary interventions are provided in our companion paper 15 . Briefly, after a one-week run-in period consuming their usual dietary intake (baseline diet), with no differences between groups at baseline for any dietary intake variable 15 , both dietary interventions significantly reduced total fat, carbohydrate, sodium, sugar, and energy intake by approximately 40% (~1000 kcals/day) from baseline levels (Fig.  1b ; Supplementary Data  1 ). By design, IF-P increased protein intake greater than CR during the intervention. The IF-P regimen consisted of 35% carbohydrate, 30% fat, and 35% protein for five to six days per week and a weekly extended modified fasting period (36–60 h) consisting of 350–550 kcals per day using randomization, as detailed previously 7 , 8 , 9 , 10 , 15 . In comparison, the CR regimen consisted of 41% carbohydrate, 38% fat, and 21% protein in accordance with current US dietary recommendations (Supplementary Table  S1 ) 14 , 16 . Using two-way factorial mixed model analysis of variance (ANOVA), significant macronutrient decreases drove energy reduction from dietary fat and carbohydrate ( p  < 0.001), with increased protein in the IF-P compared to CR ( p  < 0.001; Supplementary Fig.  S1b ; Supplementary Data  1 ). Regarding GI functioning and GM modulation, IF-P significantly decreased sugar and increased dietary fiber relative to CR (IF-P; pre, 20 ± 2 vs. post, 26 ± 2: CR; pre, 24 ± 3 vs. 24 ± 2 g/day; p  < 0.05). Despite similar average weekly energy intake (~9000 kcals/week) and physical activity energy expenditure (~350 kcals/day; p  = 0.260) during the intervention, participants following the IF-P regimen lost significantly more body weight (−8.81 ± 0.71% vs. −5.40 ± 0.67%; p  = 0.003; Fig.  1c ; Supplementary Data  1 ) and total, abdominal, and visceral fat mass and increased fat-free mass percentage (~2×; p  ≤ 0.030), as previously reported 15 . In addition, within-group analyses revealed a significant decrease in the reported frequency of total and lower-moderate GI symptoms (GI symptom rating score [GSRS] ≥4) over time for both IF-P and CR participants. However, when comparing the two dietary interventions at each time point, a more substantial reduction was observed in IF-P participants compared to CR participants (i.e., −9.3% vs. −5.4% and −13.2% vs. −3.9%, respectively; Table  1 ). The increased protein and lower sugar intake in IF-P compared to CR may have favorably mediated the GM and symptomatology.

a Study design with baseline participant characteristics. A registered dietitian counseled individuals from both groups each week. Time points with data collection are shown for both IF-P and CR participants. Icons created using BioRender.com. b Total daily caloric intake at each time point was not significantly different between IF-P and CR diet groups (two-sided Student’s t -test, p  < 0.05). Adjusted values are displayed by dividing total weekly intake by seven, to account for the fasting periods of IF-P. c IF-P participants lost significantly more weight over time versus CR participants. Points connected by line represent percent of weight compared to baseline weight for each participant. d Overall gut microbial colonization, as demonstrated by qPCR-based quantification of 16S rRNA gene copies per gram wet weight was unaffected by time or intervention (linear-mixed effects [LME] model, two-sided p  > 0.05). Alpha diversity metrics, e observed amplicon sequence variants (ASVs), and f Phylogenetic diversity at the ASV level significantly increased over time, independent of the intervention. g Intra-individual changes in GM community structure from baseline to weeks four and eight in IF-P participants shifted significantly throughout the IF-P intervention compared to CR as measured by the Bray-Curtis dissimilarity index (two-sided Wilcoxon rank-sum test). All box and whiskers plots display the box ranging from the first to the third quartile, and the center the median value, while the whiskers extend from each quartile to the minimum or maximum values. Heatmap of significant changes in h family- and i genus-level bacter i a by intervention. Colors indicate the within-group change beta coefficients over time for each cell, and asterisks denote significance. Black-white annotations on the bottom denote the significance of between-group change difference (by MaAsLin2 group × time interactions; p -values were corrected to produce adjusted values [ p .adj] using the Benjamini–Hochberg method). For all panels, IF-P: n  = 20, CR: n  = 19. Source data are provided as a Source Data file.

The substantial reduction in calorie intake of both groups (~40% from baseline) led us to investigate its potential impact on transient microbial colonization in the gut, as estimated by 16S rRNA gene copies (linear-mixed effects model [LME] time effect, p  = 0.114; Fig.  1d ; Supplementary Data  2 ). While it might be expected that a significant reduction in calorie intake could influence gut microbial colonization, our findings indicate that this reduction did not reach statistical significance within the timeframe of our study. This result contrasts with previous research that imposed more substantial energy restriction, such as a four-week regimen of ~800 kcal/day in participants with overweight/obesity, where overall gut microbial colonization notably decreased 4 . In addition to assessing microbial colonization, we also investigated whether the calorie reduction significantly influenced principal stool characteristics, including wet stool weight, Bristol stool scale (BSS), and fecal pH ( p  ≥ 0.066; Table  1 ). However, we did not observe statistically significant changes in these parameters over the course of the study. Moreover, there were no significant differences between the two dietary intervention groups over time (interaction effect, p  ≥ 0.051). In contrast, there were significant time effects for observed amplicon sequence variants (ASVs) and phylogenetic diversity (LME time effect, p  ≤ 0.023; Fig.  1e, f ; Supplementary Data  2 ), with values increasing at weeks four and eight compared to baseline (pairwise comparisons, p  ≤ 0.048); however, no interaction was observed for either alpha diversity metric (group × time effect, p  ≥ 0.925). To rule out the potential confounding effects of GI transit time 17 , BSS (as a surrogate marker) and stool pH were not significantly correlated with alpha diversity (Spearman correlations, p  ≥ 0.210). In relation to community composition, much of the intervention variance could be attributed to individual response upon testing nested permutational analysis of variance (PERMANOVA; R 2  = 0.749, p  = 0.001; Supplementary Table  S2 ), showcasing the highly individualistic landscape of the human GM in response to dietary intervention. However, a significant 1.8% of the variance was accounted for by the group × time interaction ( p  = 0.001). Moreover, individual responses over time showed variance between the two dietary interventions (PERMANOVA, R 2  = 0.123, p  = 0.003). This variability was apparent by assessing intra-individual differences, where a pronounced increase in Bray-Curtis dissimilarity was observed in the IF-P compared to the CR group after four (median Bray-Curtis dissimilarity, 0.53 [IQR: 0.47–0.61] vs. 0.38 [IQR: 0.33–0.47]) and eight weeks (0.50 [IQR: 0.41–0.55] vs. 0.39 [IQR: 0.33–0.45]; Fig.  1g ; Wilcoxon rank-sum test, p  ≤ 0.005).

To understand the taxa driving this GM variation from baseline to weeks four and eight between the two dietary interventions, we constructed MaAsLin2 linear-mixed models with the individual participant as a random factor 18 . We observed differential abundance patterns at the family and genus level in response to the IF-P but not the CR intervention. Of the 28 family and 69 genus-level features captured after filtering, a respective total of six and 18 taxa displayed significant interaction effects, with all significant time effects occurring from IF-P ( p .adj ≤ 0.10; Fig. 1h, i ; Supplementary Data  3 , 4 ). Notably, the changes observed at the four-week mark were more pronounced compared to those at eight weeks. These early alterations may signify an initial adaptation phase during which microbial populations respond to the modified substrate availability and nutrient composition, suggesting a degree of community resilience 19 . Increases were sustained to the third fecal collection for the family Christensenellaceae and the genera Incertae Sedis ( Ruminococcaceae family), Christensenellaceae R-7 group , and UBA1819 ( Ruminococcaceae family) (effect size > 2.0). Christensenellaceae is well regarded as a marker of a lean (anti-obesity) phenotype 20 and is associated with higher protein intake 21 . Other notable increases included Rikenellaceae , which, like Christensenellaceae , has been linked to reduced visceral adipose tissue and healthy metabolic profiles 22 , and Marvinbryantia , a candidate marker for predicting long-term weight loss success in individuals with obesity 23 . In addition, IF-P increased Ruminococcaceae , which has been noted to have an increased proteolytic and lipolytic capacity 24 . This shift in IF-P participants likely represents a change in GM substrate fermentation preferences as the diet regimen (relative protein and carbohydrate) and energy restriction is expected to increase the proteolytic: saccharolytic potential ratio 25 . In contrast, all taxa that decreased in IF-P participants were butyrate producers. These included the family Butyricicoccaceae and several genera such as Butyricicoccus (week four), Eubacterium ventriosum group (weeks four and eight), and Agathobacter (week four) (effect size < −2.0). When comparing monozygotic twin pairs, Eubacterium ventriosum group and another reduced genus, Roseburia , were more abundant in the higher body mass index (BMI) siblings 26 . Others, such as the mucosa-associated Butyricicoccus and Erysipelotricaceae UCG-003, have been positively correlated with insulin resistance and speculated to contribute to impaired glycolipid metabolism 27 .

Despite these changes in GM composition and increased fiber intake (+30% vs. baseline) of the IF-P participants 15 , we did not detect a significant shift in the abundance of the principal fecal short-chain fatty acids (SCFAs), acetate, propionate, butyrate, or valerate, as assessed by gas chromatography-mass spectrometry (GC–MS) (LME, p  ≥ 0.470; Supplementary Fig.  S1c ; Supplementary Data  5 ). Several factors likely contribute to this finding. For example, the distinct physical-chemical properties of fiber sources between IF-P and CR are inherently different. Participants adhering to the IF-P diet consumed most of their dietary fiber as liquid meal replacements (shakes) that are rich in non-digestible, oligosaccharide dietary-resistant starch 5 (RS5). In contrast, subjects on the CR regimen consumed their fiber from whole food sources such as vegetables, whole grains, and legumes. These fiber sources provided a mixture of soluble and insoluble fibers and a more complex fiber profile than IF-P participants. Moreover, even similar fiber profiles may function differently due to differences in food matrices and/or food preparation (cooking, raw consumption, etc.). Also of relevance is the timing of their fiber consumption. IF-P participants’ fiber intake was concentrated in fiber-rich shakes, offering immediate availability of fiber to the GI tract. In contrast, CR participants consumed fiber through whole foods, leading to a slower digestion and absorption process influenced by individual digestive transit times and enzymatic profiles. Interestingly, our results parallel recent work where participants more than doubled their fiber intake without affecting fecal SCFAs 28 . The disparate findings may be due to the type of dietary-resistant starch (RS) as a component of the nutrition regimen. In the current study, RS5 was included in the meal replacement shakes (eight grams/shake, two shakes/day, 16 g/day total). Prior research supports resistant starch intakes of >20 g/day favorably modulate SCFA production, primarily butyrate, over four to 12-week interventions 29 , 30 . Moreover, this lack of response in fecal SCFAs in both groups may have been further compounded by the significant reduction in energy intake in both groups, where the epithelia of the GI tract may have absorbed any potential increase in SCFAs from the dietary shift. It is worth noting that stool analysis may not be the most reliable biological surrogate for capturing SCFA flux over time 28 . Nevertheless, the changes in nutrient quality, timing, ratios, and the observed shift toward proteolytic activity suggest that the luminal matrix of digesta in the IF-P group impacted substrate availability for GM. This effect appears to be an influencing force in driving the observed beneficial shifts in microbial communities, such as Christensenellaceae and Incertae Sedis , as well as improvements in GI symptomatology in IF-P compared to CR. These results underscore the complexity of dietary influences on GM and highlight the need for further research to explore the impact of liquid meal replacements versus whole food sources on GM changes and SCFA status.

IF-P modulates circulating cytokines and gut microbiome taxa compared to CR

Caloric restriction and WL have been well known to positively influence inflammatory cytokine expression, with GM now emerging as an important modulator 31 . Surveying a panel of 14 plasma cytokines, we noted significant interaction (group × time) effects for IL-4, IL-6, IL-8, and IL-13 (LME, p  ≤ 0.034; Fig.  2a–d ; Supplementary Table  S3 ; Supplementary Data  6 ). These cytokines exhibited increases at weeks four and/or eight compared to baseline exclusively in the IF-P group (pairwise comparisons, p .adj ≤ 0.098), while no significant changes were observed in the CR group ( p .adj ≥ 0.562). Notably, IL-4 has been reported to display lipolytic effects 32 , and IL-8 has been positively associated with weight loss and maintenance 33 . Regarded as a proinflammatory myokine, IL-6 can acutely increase lipid mobilization in adipose tissue under fasting or exercise conditions 34 , 35 , 36 . IL-13 may be important for gut mucosal immune responses and is a stimulator of mucus production from goblet cells 37 , which has been recently reported to be influenced during a two-day-a-week fasting regimen in mice 38 . These results were of note considering the significant total body weight, fat, and visceral fat loss in the IF-P compared to the CR group. Surprisingly, correlational analysis with change (post – pre) in anthropometric and select plasma biomarker values with the cytokine profile did not reveal any significant associations after correcting for multiple testing effects ( p .adj ≥ 0.476; Supplementary Data  7 ). Plasma cytokines were, however, correlated with microbial composition for samples collected in the IF-P group during the intervention period (weeks four and eight) using graph-guided fused least absolute shrinkage and selection operator (GFLASSO) regression, revealing associations between cytokine-taxa pairs (Supplementary Fig.  S2a ). Of the four cytokines that increased in IF-P participants, we identified multiple significant correlations: Colidextribacter (rho = −0.55, p .adj = 0.015), Ruminococcus gauvreauii group (rho = 0.50, p .adj = 0.036), and Intestinibacter (rho = 0.45, p .adj = 0.086) with IL-4 (Supplementary Fig.  S2b ) and an unclassified genus from Oscillospiraceae (rho = −0.53, p .adj = 0.019), Colidextribacter (rho = −0.52, p .adj = 0.019), and Ruminoccus gauvreauii group (rho = 0.51, p .adj = 0.019) with IL-13 (Supplementary Fig.  S2c ).

a IL-4, b IL-6, c IL-8, and d IL-13: Each panel shows the cytokine concentration levels. Significant time effects and interaction effects (group × time) were detected using linear-mixed effects models (LME, two-sided p  < 0.05), indicating differential changes over the intervention period. IF-P participants exhibited significant increases in cytokine levels compared to baseline, as evidenced by pairwise comparisons adjusted for multiple testing using the Benjamini–Hochberg method (two-sided p .adj < 0.10). All box and whiskers plots display the box ranging from the first to the third quartile, and the center the median value, while the whiskers extend from each quartile to the minimum or maximum values. For all panels, IF-P: n  = 20, CR: n  = 19. Source data are provided as a Source Data file.

Displaying negative correlations for IL-4 and IL-13, Colidextribacter has been shown to be positively correlated to fat accumulation, insulin, and triglyceride levels in mice fed a high-fat diet 39 and positively correlated with products of lipid peroxidation, suggesting its potential role in promoting oxidative stress 40 . Conversely, Ruminoccus gauvreauii group was positively correlated with IL-4 and IL-13. Although limited information is available regarding the host interactions of this microbe, this genus is considered a commensal part of the core human GM and able to convert complex polysaccharides into a variety of nutrients for their hosts 41 . While these findings highlight the potential interplay between specific microbes and cytokine profiles, the directional influence—whether microbial changes drive cytokine alterations or vice versa—cannot be determined in this study setting. Furthermore, despite the change in cytokine profiles in the IF-P group, we did not detect any significant time or group × time effects when measuring lipopolysaccharide-binding protein (LBP; Δ pre/post, IF-P: 0.24 ± 0.31 vs CR: −0.93 ± 0.49 μg/mL; p  ≥ 0.254), a surrogate marker for gut permeability 42 . While the GM plays a crucial role in modulating the gut-immune axis, the observed cytokine fluctuations and microbial associations might also involve other factors. These include the production of specific metabolites due to shifts in microbial composition as well as the influence of the dietary regimen itself, which may have a central role in shaping these interactions.

IF-P and CR yield distinct circulating metabolite signatures and convergence of multiple metabolic pathways

To understand the potential differential impact of IF-P versus CR on the host, we surveyed the plasma metabolome, reliably detecting 136 plasma metabolites across 117 samples (i.e., QC CV < 20% and relative abundance > 1000 in 80% of samples). Based on outlier examination (random forest [RF] and principal component analysis [PCA]), no samples were categorized as outliers, and all data were retained for subsequent analysis. Metabolomic profile shifts were observed in both IF-P and CR groups compared with baseline (Canberra distance), however, these did not differ significantly by group or time (weeks four and eight; Wilcoxon rank-sum test, p  ≥ 0.087; Supplementary Fig.  S3a ). We prepared a general linear model (GLM) with age, sex, and time as covariates and corrected for false discovery rate (FDR). When controlling for these relevant covariates, we observed significant differences between IF-P and CR for 15 metabolites (Fig.  3a , Supplementary Table  S4 ): 2,3-dihydroxybenzoic acid, malonic acid, choline, agmatine, protocatechuic acid, myoinositol, oxaloacetic acid, xylitol, dulcitol, asparagine, n-acetylglutamine, sorbitol, cytidine, acetylcarnitine, and urate ( p .adj ≤ 0.089). To estimate the univariate classification performance of the 15 significant metabolites, we performed a receiver operating characteristic (ROC) analysis. Ten metabolites demonstrated a moderate area under the curve (AUC) (0.718–0.819), while five metabolites had an AUC < 0.70. Therefore, to improve classification performance, we constructed a supervised PLS-DA model using levels of the 15 significant metabolites ( p .adj ≤ 0.089) and analyzed variable importance in projection (VIP) scores (Supplementary Fig.  S3b ). Five metabolites with a VIP > 1.0 (2,3-dihydroxybenzoic acid, malonic acid, protocatechuic acid, agmatine, and myoinositol) were retained to construct an enhanced orthogonal projection to latent structures discriminant analysis (OPLS-DA) model. In contrast, the model fit was assessed with 100-fold leave-one-out cross-validation (LOOCV; see “Methods” section). Permutation testing showed the refined OPLS-DA model to have an acceptable fit to data ( Q 2  = 0.460, p  < 0.001), with appreciable explanatory capacity ( R 2  = 0.506, p  < 0.001; Supplementary Fig.  S3c ). The ROC analysis produced an area under the curve (AUC) of 0.929 (95% CI: 0.868–0.973, sensitivity = 0.8, specificity = 0.9; Supplementary Fig.  S3d ) between the CR and IF-P groups showing good accuracy of the GLM and providing strong support for the differential expression of these 15 metabolites between groups.

a Abundance and log fold-change of significant plasma metabolites between IF-P and CR groups as determined by a general linear model (GLM) adjusted for age, sex, and time. All GLM analyses utilized two-sided p -values, with multiple testing corrections applied using the Benjamini–Hochberg method ( p .adj). Metabolome pathway analysis was conducted for b IF-P and c CR using all reliably detected metabolites showing significantly altered pathways ( p .adj < 0.10) with moderate and above impact (>0.10). Impact scores were calculated using a hypergeometric test, while significance was assessed via a test of relative betweenness centrality, emphasizing the changes in metabolic network connectivity. For all panels, IF-P: n  = 20, CR: n  = 19. Source data are provided as a Source Data file.

Two metabolites, malonic acid, and acetylcarnitine, increased compared to the CR intervention. Several other investigators have noted the increase in acetylcarnitine via fasting protocols 43 , 44 . This increase is consistent with free fatty acid mobilization and increased transportation of these fatty acids via carnitine acylation into the mitochondria for fatty acid oxidation. These results would also be consistent with the expected ketogenesis, although not documented in our study, but noted by similar fasting interventions 44 . Relatedly, malonic acid, a naturally occurring organic acid, is a key regulatory molecule in fatty acid synthesis via its conversion to acetoacetate; hence, our results may reflect this increased synthesis in response to the mobilization and oxidation of fatty acids occurring during fasting. Other metabolites that decreased with IF-P include several sugar alcohols (myoinositol, dulcitol, and xylitol). Dulcitol (galactitol) is a sugar alcohol derived from galactose. It is possible that during fasting, levels of dulcitol decrease as glucose (initially) and free fatty acids (after 24–36 h of fasting) are preferentially utilized as energy substrates. One amino acid (asparagine) and one amino acid analog (N-acetylglutamine, associated with consumption of a Mediterranean diet 45 ) also decreased with IF-P relative to CR. Finally, 2,3-dihydroxybenzoic acid significantly decreased with IF-P. This metabolite is formed during the metabolism of flavonoids, as it is found abundantly in fruits, vegetables, and some spices. At the cellular level, this hydroxybenzoic acid functions as a cell signaling agent and has been speculated as a potentially protective molecule in various cancers 46 . It is unclear whether this metabolite decreased due to either dietary intake or metabolic processes related to high-protein intake or the fasting protocol. Collectively, the metabolic responses to these dietary regimens reflect the interrelationships of several anabolic and catabolic physiologic responses to three key components of these interventions: (a) the WL process itself, (b) changes in amount (and type) of macronutrient distribution (i.e., meal replacement shakes vs. whole food diet approach; higher vs. normal protein intakes), and (c) the adherence to fasting (IF-P only).

To determine the significantly impacted pathways of the dietary interventions, we grouped participant samples according to baseline or intervention period (weeks four and eight), with IF-P and CR assessed separately. A total of 14 pathways were significant in the IF-P group ( p .adj < 0.10; Fig.  3b ), with three displaying large impact coefficients (>0.5): (1) Glycine, serine, and threonine metabolism, (2) alanine, aspartate, and glutamate metabolism, and (3) ascorbate and aldarate metabolism. In comparison, 24 pathways were significant for the CR group (Fig.  3c ), with four showing large impact coefficients (>0.5): (1) Phenylalanine, tyrosine, and tryptophan biosynthesis, (2) alanine, aspartate, and glutamate metabolism, (3) citrate cycle (TCA cycle), and (4) glycine, serine and threonine metabolism. Notably, the glycine, serine, and threonine pathway has recently been found in preclinical models to play a pivotal role in longevity and related life-sustaining mechanisms independent of diet, though heavily impacted by fasting time and caloric restriction 47 . This may be partially related to the ability of glycine to increase tissue glutathione 48 , 49 and protect against oxidative stress 50 . In our analysis, this pathway was significant in both diet groups and is biochemically and topologically related to the additionally captured amino acid pathway, alanine, aspartate, and glutamate metabolism, as well as the energy-releasing pathway, the citrate cycle (TCA cycle). Notably, in the CR group, phenylalanine, tyrosine, and tryptophan biosynthesis, are important for neurotransmitter production and reported to be suppressed (tryptophan) in obesity 51 . This representation may have also been attributed to the differences in protein intake 52 or differences in dietary diversity 53 , yet to be determined. Regardless, we noted similar representations of pathway impact between IF-P and CR, with metabolic response centered on utilization of amino acids in addition to lipid turnover and energy pathways.

Gut microbiome and plasma metabolome latent factors indicate differential multi-omic signatures between IF-P and CR regimens

As the plasma metabolome has been suggested as a bidirectional mediator of GM influence on the host 54 , we performed a multi-omics factor analysis (MOFA) 55 to identify potential patterns of covariation and co-occurrence between the microbiome and circulating metabolites. Operating in a probabilistic Bayesian framework, MOFA simultaneously performs unsupervised matrix factorization to obtain overall sources of variability via a limited number of inferred factors and identifies shared versus exclusive variation across multiple omic data sets 55 . Eight latent factors were identified (minimum explained variance ≥2%; see “Methods” section), with the plasma metabolome and GM explaining 37.12% and 17.49% of the overall sample variability, respectively (Fig.  4a ). Based on significance and the proportion of total variance explained by individual factors for each omic assay, Factors 1 ( R 2  = 11.98) and 6 ( R 2  = 5.28) captured the greatest covariation between the two omic layers (Fig.  4a ; Supplementary Table  S5 ). In contrast, Factors 2 and 5 were nearly exclusive to the metabolome, and factors 3 and 4 to the GM. Interestingly, Factor 1 was significantly negatively correlated to dietary protein intake (Spearman rho = −0.270, p.adj = 0.021; Fig.  4b ) and captured the variation associated with the CR diet (Wilcoxon rank-sum test, p .adj = 3.2e-04; Fig.  4c ). Factor 6 had the greatest number of significant correlations, including negative associations with visceral adipose tissue, waist circumference, body weight, BMI, fat mass, android fat, subcutaneous adipose tissue, dietary sodium, carbohydrate, fat, energy intake (kcal), and sugar (Spearman rho ≤ −0.220, p .adj ≤ 0.075) and captured the variation associated with IF-P (Wilcoxon rank-sum test, p .adj = 0.007).

a The cumulative proportion of total variance explained ( R 2 ) and proportion of total variance explained by eight individual latent factors for each omic layer. b Spearman correlation matrix of the eight latent factors and clinical anthropometric and dietary covariates. Each circle represents a separate association, with the size indicating the significance (-log10 ( p -values)) and the color representing the effect size (hue) with its direction (red: positive; blue: negative). All correlations are calculated using two-sided tests. Asterisks within a circle denote significance after adjustment with the Benjamini–Hochberg method. c Scatter plot of Factors 1 and 6, with each dot representing a sample colored by intervention. Box and whisker plots illustrate significant differences between groups after adjusting for multiple testing using the Benjamini–Hochberg method (Wilcoxon rank-sum test; top = Factor 1, p .adj = 3.2e-04; right = Factor 6, p .adj = 0.007). The plots show boxes ranging from the first to the third quartile and the median at the center, with whiskers extending to the minimum and maximum values. d Factor 1 and 6 loadings of genera and metabolites with the largest weights annotated. Symbols: * p .adj < 0.10, ** p .adj < 0.01, *** p .adj < 0.001, **** p .adj < 1.0e-04. For all panels, IF-P: n  = 20, CR: n  = 19. Source data are provided as a Source Data file.

Assessing the positive weights (feature importance) of Factor 1 revealed a microbial and metabolomic signature linked with CR, including the taxa Faecalibacterium , Romboutsia , and Roseburia , and the plasma metabolites myoinositol, agmatine, N-acetylglutamine, erythrose, and mucic acid (Fig.  4d ). Previous dietary restriction studies have reported co-occurrence of gut microbial taxa and plasma metabolites that span a wide variety of applications and investigations 56 . The specific co-occurrences observed in Factor 1 exhibited an abundance of butyrate-producing bacterial taxa that utilize carbohydrates as their predominant substrate and plasma metabolites that are generally involved in carbohydrate metabolism, such as erythrose, an intermediate in the pentose phosphate pathway (PPP), and mucic acid which is derived from galactose and/or galactose-containing compounds (i.e., lactose). These co-occurrence patterns biologically cohere considering the nutritional profile of the CR group and the large contribution of fiber-rich, unrefined carbohydrates and reduction in sugar (~50% kcal from sugar). Indeed, these nutritional changes may have influenced the GM to accommodate changes in dietary substrate more efficiently. One interesting co-occurrence was the genus Romboutsia and metabolite N-acetylglutamine. Romboutsia has been shown to produce several SCFAs and ferment certain amino acids, including glutamate 57 . N-acetylglutamine is biosynthesized from glutamate; thus, its co-occurrence with the abundance of Romboutsia encourages further exploration into this interaction 58 .

Factor 6 captured the signature associated with IF-P, with positive contributions from the taxa Incertae Sedis ( Ruminococcaceae family), Erysipelatoclostridium , Christensenellaceae R-7 group , Oscillospiraceae UCG-002, and Alistipes , and the plasma metabolites malonic acid, adipic acid, succinate, methylmalonic acid, and mucic acid (Fig.  4d ). Prior work has established that Alistipes increases from diets rich in protein and fat, and contributes to the highest number of putrefaction pathways (i.e., fermentation of undigested proteins in the GI tract) over the other commensals 59 . This could explain the co-occurrence of plasma metabolites from protein catabolism, such as 2-aminoadipid acid, adipic acid, and glutamic acid 22 , 59 . Oscillospiraceae has recently been viewed with next-generation probiotic potential, harboring positive regulatory effects in areas related to obesity and chronic inflammation 60 . Mentioned prior, recent studies have reported on the role of Christensenellaceae on human health, participating in host amino acid and lipid metabolism as well as fiber fermentation 20 , with Christensenellaceae R-7 group notably evidenced to correlate with visceral adipose tissue reduction 22 . As such, the elevated abundance of microbes in the GM of IF-P participants observed in this study in tandem with the co-occurrence of metabolites indicative of protein degradation and mobilization and oxidation of fatty acids, such as methylmalonic acid, malonic acid, and succinate, presents a nascent multi-omic signature of IF-P. In addition, and more pronounced in the IF-P vs CR group, participants decreased sugar intake by ~75% (kcals) compared to baseline levels. Considering the other regimental components of IF-P, the differences in multi-omic signatures likely display the selective pressures of these two interventions.

Gut microbiome (GM) composition is associated with weight loss (WL) responsiveness to IF-P diet

The IF-P intervention produced a microbiome and metabolomic response; however, the loss in body weight and fat across individuals varied (Fig.  5a ). To provide deeper characterization and explore differential features of WL responsiveness, we performed a GM-focused subgroup analysis by employing shotgun metagenomic and untargeted fecal metabolomic surveys in 10 individuals that either achieved ≥10% loss in body weight or bordered on clinically important WL (i.e., >5% BW; herein, ‘High’ and ‘Low’ responders) 61 . Importantly, baseline characteristics between WL responder classification did not differ significantly (baseline body weight: High, 108.9 ± 30.8 vs. Low, 81.9 ± 18.1 kg, p  = 0.117; Supplementary Table  S6 ). Assessing the GM at the fundamental taxonomic rank, species composition showed significant separation by weight loss response evaluated by Bray-Curtis dissimilarity (group × time: R 2  = 0.114, p  = 0.001; Fig.  5b ; Supplementary Table  S7 ), with most of the variation explained by the individual ( R 2  = 0.711, p  = 0.001). In comparison, species level alpha diversity did not differ significantly between classifications (group × time: p  ≥ 0.674; Fig.  5c, d ). Identifying 212 species after filtering, we noted significant differences in bacterial abundances between groups over time (Fig.  5e ; Supplementary Data  8 ). A total of 10 features increased in the High-responder group relative to the Low-response group over the eight-week study period, including Collinsella SGB14861 , Clostridium leptum , Blautia hydrogenotrophica , and less typified species; GGB74510 SGB47635 (unclassified Firmicutes), GGB3511 SGB4688 (unclassified Firmicutes), Faecalicatena contorta , Lachnospiraceae bacterium NSJ-29 , Phascolarctobacterium SGB4573 , GGB38744 SGB14842 (unclassified Oscillospiraceae ), and Massiliimalia timonensis (effect size ≥ 1.163, p .adj ≤ 0.092). The increase in Collinsella , a less characterized anaerobic pathobiont that produces lactate and has been associated with low-fiber intakes 62 , 63 and lipid metabolism 64 , may have been related to the periods of CR and IF, in conjunction with the greater influx of host-released fatty acids in the High-responder group. Relatedly, Clostridium leptum growth has been linked with increases in monounsaturated fat intake, reductions in blood cholesterol 65 , and stimulation of Treg induction (i.e., anti-inflammatory) 66 . The latter association is relevant to the SCFA-promoting (primarily butyrate) qualities of Clostridium leptum 67 . Blautia hydrogenotrophica , an acetogen with bidirectional metabolic cross-feeding properties (e.g., transfer of hydrogen and acetate), is also important for butyrate formation 68 . Taxa that decreased relative to the Low-responder group; Eubacterium ventriosum , Streptococcus salivarius , Eubacterium rectale , Anaerostipes hadrus , Roseburia inulinivorans , Mediterraneibacter glycyrrhizinilyticus , and Blautia massiliensis (effect size ≤ −1.690, p .adj ≤ 0.078), included butyrate producers, Eubacterium ventriosum , Eubacterium rectale , Roseburia inulinivorans , and others, such as Streptococcus salivarius , a nuclear factor kappa B (NF-κB) activity repressor 69 and Peroxisome proliferator-activated receptor gamma (PPARγ) inhibitor potentially influencing lipid and glucose metabolism 70 . Investigating monozygotic (MZ) twin pairs, Eubacterium ventriosum was more abundant in the higher BMI siblings 26 , with enhanced scavenging fermentation capabilities 71 . Roseburia inulinivorans is a mobile firmicute (flagella) that harbors a wide-ranging enzymatic repertoire able to act on various dietary polysaccharide substrates suggestive of the ability to respond to the availability of alternative dietary substrates 72 . While we noted a more variable shift in fecal total SCFAs, acetate, propionate, butyrate, or valerate (via targeted GC–MS), in the Low weight loss responders, there was no significant difference when compared to High weight loss responders (Wilcoxon rank-sum test, p  ≥ 0.210; Supplementaryl Fig.  S4a ; Supplementary Data  9 ).

a Relative weight loss over the eight-week intervention for each participant in the IF-P group. b NMDS ordination showed the personalized trajectories of participants’ microbiomes over time. Dotted lines connect the same individual and point toward the final sample collection. No significant time or group × time interaction effects for alpha diversity metrics, c observed species, and d the Shannon index. Box and whiskers plots display the box ranging from the first to the third quartile, and the center the median value, while the whiskers extend from each quartile to the minimum or maximum values. Volcano plots displaying differential abundance between High and Low weight loss responders for e microbial species and f functional pathways. Significant features were more enriched in High and Low weight loss responders colored orange and light blue, respectively. g Alluvial plot displaying the fecal metabolite profile at the subclass level (Human Microbiome Database). Most abundant metabolite subclasses displayed (i.e., ≥1%). Metabolome pathway analysis for h High and i Low weight loss responders using all reliably detected fecal metabolites showing altered pathways with moderate and above impact (>0.10). Impact was calculated using a hypergeometric test, while significance was determined using a test of relative betweenness centrality. j Grid-fused least absolute shrinkage and selection operator (GFLASSO) regression of species from differential abundance analysis displayed correlative relationships with fecal metabolites. Species with greater abundance in High (High > Low) and Low (Low > High) weight loss responders are separate‘. For all panels, High: n  = 5, Low: n  = 5. Source data are provided as a Source Data file.

Less affected compared to taxonomic features were the 275 microbial-affiliated metabolic pathways identified after filtering, of which gluconeogenesis III and guanosine ribonucleotides de novo biosynthesis were increased (effect size ≥ 0.108, p .adj = 0.079), while super pathway of L-alanine biosynthesis, sucrose degradation IV (sucrose phosphorylase), sucrose degradation III (sucrose invertase), super pathway of thiamine diphosphate biosynthesis III, and flavin biosynthesis I (bacteria and plants) were decreased in the High relative to the Low weight loss responder group (effect size ≤ −0.247, p .adj ≤ 0.079; Fig.  5f ; Supplementary Data  10 )

As the difference in microbial shifts versus function is well established, we also tracked the fecal metabolome to better understand metabolic modification/production and identify potential microbial metabolic targets for future weight loss interventions. Overall, we reliably detected (QC relative standard deviation > 20% and mean intensity value > 1000 in 80% of samples) and annotated 607 (Human Metabolome Database) compounds across fecal samples. Notably, we found the fecal metabolite profile of both subgroups abundant in amino acids, peptides, and analogs, with decreases in sulfates, furanones, and quaternary ammonium salts and increases in cholestane steroids, carboxylic acid derivatives, and imidazoles (Fig.  5g ). Assessing metabolite changes between groups did not yield significance when comparing logFC values (Wilcoxon rank-sum test, p .adj > 0.10; Supplementary Fig.  S4b ). Pathway analysis of High weight loss responders revealed prominent metabolic signatures relevant to lipid metabolism (glycerolipid and arachidonic metabolism), nucleotide turnover (pyrimidine metabolism), and aromatic amino acid formation (phenylalanine, tyrosine, and tryptophan biosynthesis; Fig.  5h , Supplementary Data  11 ). In comparison, the more prominent enriched pathways for Low weight loss responders included those related to amino acid and peptide metabolism (glycine, serine, and threonine, d-glutamine and d-glutamate, and tyrosine metabolism and arginine biosynthesis; Fig.  5i , Supplementary Data  12 ).

Finally, species captured by our differential abundance analysis were channeled into a GFLASSO model with the fecal metabolome library to select metabolically relevant compounds best predicted by microbial abundances. Restricting taxa and metabolites displaying stronger co-occurrence signals (GFLASSO coefficients > 0.02), we noted several patterns (Fig.  5j ). This included positive associations between GGB3511 SGB4688 (unclassified Firmicute) and malonic acid (important to fatty acid metabolism), as well as Roseburia inulinivorans and 3-Hydroxy-2-oxo-1H-indole-3-acetic acid. Negative associations included Phascolarctobacterium SGB4573 with the fatty acid ester, methyl sorbate, and Streptococcus salivarius (anti-inflammatory) with leukotriene B4 dimethylamide.

Differences detected in our subgroup analysis suggest that the GM composition plays a role in WL responsiveness during IF-P interventions. Notable differences in taxa and fecal metabolites suggest differing substrate utilization capabilities and nutrient-acquiring pathways between High and Low responders, despite being on the same dietary regimen. Although differences between High and Low responders were statistically significant for the microbiome data, the magnitude of differences varied, suggesting further research is needed to clarify these differences.

Long-term IF-P remodels the gut microbiome after substantial weight loss – A case study

Considering the microbiomic and metabolic importance of sustained WL, we additionally performed a longitudinal, exploratory case study analysis on the participant who lost the most body weight during the eight-week WL period (−15.3% BW, −24.9 kg). Under rigorous clinical supervision, this individual was guided through and comprehensively tracked over 52 weeks, strictly adhering to an IF-P regimen, including WL (0–16 weeks) and maintenance (16–52 weeks) periods, which included adjusting the calorie intake to maintain energy balance. Microbial richness and evenness at the species level displayed a general inverse trend with body weight reduction, although they converged at 52 weeks (Fig.  6a, b ). Species dissimilarity peaked at weeks four and 16, after which it plateaued, but remained consistently higher in comparison to baseline over the 52-week period (Fig.  6c ). Examining positive linear coefficients of a PERMANOVA model, constructed to detect variation between community compositions over time, dominant influences included several species within the Lachnospiraceae family such as Fusicatenibacter saccharivorans , Blautia wexlerae , Blautia massillensis , Anaerostipes hadrus , and Coprococcus comes and others like Akkermansia muciniphila (Fig.  6d ). Negative contributions included species from the Oscillospiraceae family, such as Ruminococcus bromii and Ruminococcus torques . Indeed, visualizing community composition over the sampling time points suggested specific GM remodeling (Fig.  6e ; Supplementary Data  13 ). Many keystone taxa prominent over time in the microbiome are highly relevant to the significant reduction in body weight and metabolic improvement of the case-study participant. For example, Blautia wexlerae , a commensal bacterium recently reported to confer anti-adipogenesis and anti-inflammatory properties to adipocytes 73 became visually more prominent over time. This association was also the case for the health-associated microbe, Anaerostipes hadrus , which converts inositol stereoisomers (including myoinositol) to propionate and acetate, apt to improve insulin sensitivity and reduce serum triglyceride levels 74 , translating to reduced host metabolic disease risk 75 . Other elevated taxa, like the mucin-degrading Akkermansia muciniphila and Bacteroides faecis , are negatively correlated with markers for insulin resistance 76 . There was also a notable bloom of Collinsella SGB14861 (anaerobic pathobiont producing lactate) 63 and suppression of Eubacterium rectale , Ruminococcus torques (associated with circadian rhythm disruption in mice) 77 , and Ruminococcus bromii (an exceptional starch degrader) 78 .

Change in alpha diversity metrics a observed species and b Shannon index with percentage of baseline body weight. c Bray-Curtis dissimilarity at the species level with d top PERMANOVA model coefficients (analysis: species~time). e Alluvial plot displaying the variation in abundance of the 20 most prevalent bacteria over time. For visual clarity, the less abundant taxa are not displayed. f Canberra distance of fecal metabolome with g top PERMANOVA model coefficients (analysis: pathway~time). h Pathway analysis of fecal metabolites comparing baseline to subsequent sample collections. Data are plotted as -log10(p) versus pathway impact. Node size corresponds to the proportion of metabolites captured in each pathway set, while node color signifies significance. Impact was calculated using a hypergeometric test, while significance was determined using a test of relative betweenness centrality. No p -value adjustments were made. Source data are provided as a Source Data file.

Compared to the more pronounced shifts in the GM, an inspection of Bray-Curtis dissimilarity at the microbial metabolic pathway level was much less affected (Supplementary Fig.  S5a ). Though positive contributions in multiple biosynthesis pathways were noted, as well as reductions in the superpathway of UDP-glucose-derived O-antigen building blocks biosynthesis and glucose and glucose-1-phosphate degradation (Supplementary Fig.  S5b ; Supplementary Data  14 ). We also tracked the fecal metabolome concordance with the GM to corroborate potential metabolic output. Shifts in metabolites captured by calculating the Canberra distance were prominent (Fig.  6f ), with positive influences from agrocybin (possessing antifungal activity 79 ), nicotinic acid (nicotinamide adenine dinucleotide precursor), and sulfate, and reductions in cadaverine (involved in the inhibition of intestinal motility 80 ), maltitol, acetohydroxamic acid (a urease inhibitor), and hypoxanthine, after removing the dominant amino acid subclass (Fig.  6g ; Supplementary Fig.  S5c ). At the chemical class level, we observed apparent shifts in chemical subclasses; cholestane steroids, amines, purines, and purine derivatives, and amino acids, peptides, and analogs (Supplementary Fig.  S5d ). Given our case-study approach, we performed a pathway analysis using all reliably detected fecal metabolites at each collection point over 52 weeks. Pathway analysis (Fig.  6h ) identified primary bile acid biosynthesis ( p  = 0.014) and cysteine and methionine metabolism ( p  = 0.096) as having the greatest significance, while the greatest impact (I) was observed in phenylalanine, tyrosine, and tryptophan biosynthesis and linoleic acid metabolism ( I  = 1.0). Alanine, aspartate, and glutamate metabolism ( I  = 0.756), vitamin B6 metabolism ( I  = 0.647), sulfur metabolism ( I  = 0.532), phenylalanine metabolism (I =  0.357), and nicotinate and nicotinamide metabolism ( I  = 0.194) also displayed marked pathway impacts (Supplementary Fig.  S5e ; Supplementary Data  15 ). Together, these integrated findings from the group comparisons (IF-P vs. CR), high vs. low responders, and the case study, suggest that the remodeling of the gut microbiome through sustained weight loss on an IF-P regimen not only alters the microbial composition but also influences key metabolic pathways and output, reflective of fat mobilization and metabolic improvement.

Our study demonstrates distinct effects of IF-P on gut symptomatology and microbiome, as well as circulating metabolites compared to continuous CR. We observed significant changes in the GM response to both interventions; however, the IF-P group exhibited a more pronounced community shift and greater divergence from baseline (i.e., intra-individual Bray-Curtis dissimilarities). This shift was characterized by increased specific microbial families and genera, such as Christensenellaceae , Rikenellaceae , and Marvinbryantia , associated with favorable metabolic profiles. Furthermore, IF-P significantly increased circulating cytokine concentrations of IL-4, IL-6, IL-8, and IL-13. These cytokines have been linked to lipolysis, WL, inflammation, and immune response. The plasma metabolome analysis revealed distinct metabolite signatures in IF-P and CR groups, with the convergence of multiple metabolic pathways. These findings shed light on the differential effects of IF regimens, including IF-P as a promising dietary intervention for obesity management and microbiotic and metabolic health.

While acknowledging individual contributions of WL, protein pacing, and IF, we propose that the beneficial shifts observed may be best characterized as the culmination of features inherent in our IF-P approach. For example, it is possible that microbial competition is leveraged during reduced and intermittent nutritional input periods, emphasizing nutrient composition and food matrix type (combination of whole food and meal replacements vs. primarily whole food), affecting available substrates for gut microbes. IF-P participants’ fiber intake was concentrated in fiber-rich (RS5 type) shakes, offering immediate availability of fiber to the GI tract. In contrast, CR participants consumed fiber through whole foods, leading to a slower digestion and absorption process influenced by individual digestive transit times and enzymatic profiles. This nutritional environment may create ecological niches that support symbiont microbial communities. In this investigation, we provide support of such remodeling, with intentional fasting and increased relative protein (protein pacing) consumption well-validated to improve body composition and metabolism during weight loss 7 , 8 , 15 . Our results align with previous studies on CR, where greater relative protein intake was associated with an increased abundance of Christensenella 81 . This increase is likely a result of increased amino acid-derived metabolites 21 . We also observed increased signatures of amino acid metabolism in the GM of IF-P participants, which may be attributed to increased nitrogen availability, prompting de novo amino acid biosynthesis. The liquid format of two of the daily meals and precise timing of high-quality protein consumption (Protein Pacing) in the IF-P regimen may have influenced these results, as amino acids play essential roles in microbial communities, acting as energy and nitrogen sources and essential nutrients for amino acid auxotrophs.

In addition to the differences in nutrient composition, the IF-P group exhibited a profound reduction (33%) in visceral fat 15 . This reduction is significant because visceral fat is highly correlated with GM. While the specific influence of GM on fat depots in our study remains unclear, the shift in cytokine profile and metabolic pathways suggests an interaction between GM and fat metabolism. Regarding GM-host interaction, we did not detect changes in gut permeability assaying LBP. However, correlations were found with cytokines IL-4 and IL-13 and microbes Colidextribacter (negative association) and Ruminoccus gauveauii group (positive association). These associations may reflect the direct impact of the dietary intervention, yet they also hint at a deeper crosstalk within the gut-immune axis. This crosstalk is known to play a pivotal role in modulating host inflammation and influencing adipose tissue signaling pathways 42 . Furthermore, the observed microbial shifts, including changes in populations of Christensenella , suggest a nuanced role for certain microbes in regulating metabolic health. Notably, certain strains of Christensenella have been implicated in the regulation of key metabolic markers, such as glycemia and leptin levels, and in promoting hepatic fat oxidation 82 .

Our findings also underscore that GM composition plays a role in WL responsiveness during IF-P interventions. Subgroup analysis based on WL responsiveness revealed significant differences in species composition at the taxonomic level. The High-responder group showed an increased abundance of certain bacteria associated with metabolic benefits and anti-inflammatory effects. In contrast, the Low-responder group exhibited an increased abundance of butyrate-producing and nutritionally adaptive species (e.g., Eubacterium ventriosum 71 and Roseburia inulinivorans 72 ). Fecal metabolome analysis further highlighted differences between the two subgroups, with distinct metabolic signatures and enrichment in specific metabolic pathways. Notably, the High WL responders displayed enrichment of fecal metabolites involved in lipid metabolism. In contrast, Low responders were more prominent in pathways related to the metabolism of amino acids and peptides, including glycine, serine, and threonine, d-glutamine, and d-glutamate, as well as tyrosine metabolism and arginine biosynthesis. The latter metabolic signature has been reported in individuals with severe obesity undergoing high-protein, low-calorie diets 83 . As both High and Low WL responders were consuming the same diet, our results suggest differences in GM composition and metabolism, which could play a role in determining the success of an IF-P regimen. Though, as these enrichment analyses were performed in an exploratory manner, we acknowledge the need for a more systematic approach to validate these findings.

Finally, we provide evidence of long-term GM stabilization from these changes by following one individual over 12 months. Dietary restriction is widely used to reduce fat mass and weight in individuals with or without obesity; however, weight regain after such periods presents a critical challenge, and the underlying homeostatic mechanisms remain largely elusive. Notably, keystone taxa that became more prominent over time were associated with anti-adipogenesis, improved insulin sensitivity, and reduced metabolic disease risk. The microbial shifts were accompanied by noticeable changes in the fecal metabolome, with shifts in various metabolites and chemical subclasses. Pathway analysis identified impacts on primary bile acid biosynthesis, cysteine and methionine metabolism, and other fat mobilization and metabolic improvement pathways. These shifts were accompanied by noticeable changes in the fecal metabolome, particularly in metabolites and chemical subclasses related to lipid metabolism, nucleotide turnover, and aromatic amino acid formation.

Despite the valuable insights from our study on the complex interactions between intermittent fasting, higher protein intake using protein pacing, the GM, and circulating metabolites in obese individuals, several limitations should be acknowledged. First, our reliance on fecal samples to represent the GM may have overlooked potential microbial populations in the upper GI tract. Including samples from proximal regions in future studies would provide a more comprehensive understanding of the gut microbiome’s response to IF-P and CR. In addition, the sample size for our study was determined based on the primary outcomes related to body weight and composition from the parent study 15 . This sample size may have reduced statistical power and potentially amplified individual variability among participants. However, it is important to note that the smaller RCT design allowed for more precise control over diet and lifestyle factors, minimizing potential confounding influences on the study outcomes. Furthermore, the study’s duration was limited to eight weeks, which prevented potential insights into the differential long-term effects between the two interventions. However, we were able to extend the follow-up duration and conduct periodic assessments for a year in our case-study participant, offering a more comprehensive understanding of the sustainability of the observed changes and the potential for weight regain for IF-P. The current study compared a combination of whole food and supplements (shakes and bars; IF-P) versus primarily whole food (CR), which together with variations in protein and fiber content and type may have influenced the gut symptomatology and nutrient absorption between groups. Additionally, study participants self-reported dietary intake daily, although there was close monitoring of intake through the return of empty food packaging/containers of consumed food and daily monitoring by investigators and weekly meetings with a registered dietitian. Overall, knowledge gaps are present in this research, including how the microbiome is rebuilt after food reintroduction and how overall caloric restriction and specific macronutrients contribute to this process. However, considering the multifactorial nature of weight loss and metabolic health, our work represents an important precedent for future work. Future investigators should consider integrating these factors to provide a more comprehensive understanding of the underlying mechanisms. Additional research is warranted to characterize the metabolic signature of IF-P, the time relationship between these fasting periods, and the analysis of these metabolic changes. A strength of our High-Low-responder and case-study analyses is the hypothesis-driving nature of the findings, from which targeted microbiome and/or precision nutrition interventions can be designed and tested.

In conclusion, our study provides valuable insights into the complex interactions among intermittent fasting and protein pacing, the GM, and circulating metabolites in individuals with obesity. Specifically, intermittent fasting - protein pacing significantly reduces gut symptomatology and increases gut microbes associated with a lean phenotype ( Christensenella ) and circulating cytokines mediating total body weight and fat loss. These findings highlight the importance of personalized approaches in tailoring dietary interventions for optimal weight management and metabolic health outcomes. Further research is necessary to elucidate the underlying mechanisms driving these associations and to explore the therapeutic implications for developing personalized strategies in obesity management. Additionally, future studies should consider investigating microbial populations in upper GI sections and potential intestinal tissue remodeling to gain a more comprehensive understanding of the gut microbiome’s role in these interventions.

Study design and participants

The protocol of the clinical trial was registered on March 6, 2020 (Clinicaltrials.gov; NCT04327141), and the results of the primary analysis have been published previously 15 . Briefly, participants were recruited from Saratoga Springs, NY, and were provided informed written consent in accordance with the Skidmore College Human Subjects Institutional Review Board before participation (IRB#: 1911-859), including consent for the use of samples and data from the current study. Each procedure performed was in adherence with New York state regulations and the Federal Wide Assurance, which follows the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research, and in agreement with the Helsinki Declaration (revised in 1983). Their physicians performed a comprehensive medical examination/history assessment to rule out any current cardiovascular or metabolic disease. For at least six months before the start of the study, all eligible participants were either sedentary or lightly active (<30 min, two days/week of organized physical activity), with overweight or obesity (BMI > 27.5 kg/m2; % body fat > 30%), weight stable (±2 kg), and middle-aged (30–65 years). In addition, participants taking antibiotics, antifungals, or probiotics within the previous two months were excluded. Enrolled participants were matched for body weight, BMI, and body fat and randomly assigned to one of two groups: (a) IF-P ( n  = 21; 14 women; 7 men) or (b) CR ( n  = 20; 12 women; 8 men) for eight weeks. During a one-week run-in period, subjects maintained a stable body weight by consuming a similar caloric intake as their pre-enrollment caloric intake while maintaining their sedentary lifestyle. This was confirmed by matching their pre-enrollment dietary intake to the one-week run-in diet period 15 . Following baseline testing, participants were provided detailed instructions on their weight loss dietary regimen (Supplementary Table  S1 ) and received weekly dietary counseling and compliance/adherence monitoring from the research team via daily food records, and weekly registered dietitian meetings, along with weekly visits to the Human Nutrition and Metabolism laboratory at Skidmore College (Saratoga Springs, NY) for meal distribution and empty packet/container returns. All outcome variables were assessed pre (week 0), mid (week 4), and post (week 8). All participants were compensated $100 for successful completion of the study and received an additional monthly stipend of $75 for groceries (CR group only) or up to two meals per day of food supplements and meal replacements (IF-P only).

IF days consisted of ~350–550 kcals per day, in which participants were provided a variety of supplements and snacks. Protein pacing (P) days for IF-P consisted of four and five meals/day for women and men, respectively, two of which (breakfast and one other meal) were liquid meal replacement shakes with added whole foods (Whole Blend IsaLean® Shakes, 350/400 kcals, 30/36 g of protein/meal, 9 g of fiber); a whole food evening dinner meal (450/500 kcals men), an afternoon snack (200 kcals, men only), and an evening protein snack (IsaLean® or IsaPro® Shake or IsaLean Whole Blend® Bar; 200–250 kcals). This dietary regimen provided 1350–1500 and 1700–1850 kcals/day for women and men, respectively, and a macronutrient distribution targeting 35% protein, 35% carbohydrate, 20–30 g/day of fiber, and 30% fat. Isagenix International, LLC (Gilbert, AZ, USA) provided all meal replacement shakes, bars, beverages, and supplements. In comparison, participants assigned to the CR diet followed specific guidelines of the National Cholesterol Education Program Therapeutics Lifestyle Changes (TLC) diet of the American Heart Association with a strong Mediterranean diet influence of a variety of fresh vegetables, fruits, nuts, and legumes. The specific macronutrient distribution recommended was <35% of kcal as fat; 50%–60% of kcal as carbohydrates; 15% kcal as protein; <200 mg/dL of dietary cholesterol; and 20–30 g/day of fiber. The total calorie intake was 1200 and 1500 calories per day for women and men, respectively, during the 8-week weight loss intervention. In addition to weekly meetings with the registered dietitian and daily contact with research team members, subjects were provided detailed written instructions for their meal plans. They were closely monitored through daily participant-researcher communication (e.g., email, text, and mobile phone), two-day food diary analysis, weekly dietary intake journal inspections, weekly meal/supplement container distribution, and returning empty packets and containers.

Gastrointestinal (GI) symptom rating scale

Participants completed the 15-question GI symptom rating scale (GSRS) 84 at baseline, week four, and week eight. Briefly, each question is rated on a 7-point Likert scale (1 = absent; 2 = minor; 3 = mild; 4 = moderate; 5 = moderately severe; 6 = severe and 7 = very severe) and recalled from the previous week. Questions include symptoms related to upper abdominal pain, heartburn, regurgitation (acid reflux), empty feeling in the stomach, nausea, abdominal rumbling, bloating, belching, flatulence, and questions on defecation. The GSRS questionnaire provides explanations of each symptom, is understandable, and has reproducibility for measuring the presence of GI symptoms 85 . In our analysis, a score of ≥2 (minor) was defined as symptom presence, and a score ≥ 4 (moderate) was defined as moderate symptom presence. Furthermore, to better categorize symptom location, bloating, flatulence, constipation, diarrhea, stool consistency, defecation urgency, and sensation of not completely emptying bowels were classified as lower GI symptoms, and nausea, heartburn, regurgitation, upper abdominal pain, empty feeling in the stomach, stomach rumbling, and belching was classified as upper GI symptoms. Total scores were also generated for overall symptom and moderate symptom presence.

Fecal sample collection and DNA extraction

Participants were instructed to provide stool samples at baseline, week four, and week eight of the intervention. The case-study participant additionally provided samples at weeks 12, 16, 32, and 52. The entire bowel movement was collected and transported within 24 h of defecation to the Skidmore College Human Nutrition and Metabolism (Saratoga Springs, NY) laboratory using a cooler and ice packs and frozen at −80 °C. Samples were then sent to ASU (Phoenix, AZ) overnight on dry ice for analysis, where they were thawed at 4 °C and processed. Wet weight was recorded to the nearest 0.01 g after subtracting the weight of fecal collection materials. Stool samples were then rated according to the BSS 86 , homogenized in a stomacher bag, and the pH was measured (Symphony SB70P, VWR International, LLC., Radnor, PA, USA). Next, the extraction of DNA was performed using the DNeasy PowerSoil Pro Kit (Cat. No. 47016, Qiagen, Germantown, MD) per the manufacturer’s instructions. DNA concentration and quality were quantified using the NanoDrop™ OneC Microvolume UV-Vis Spectrophotometer (Thermo Scientific™, Waltham, MA) according to manufacturer instructions. The OD 260 /OD 280 ratio of all samples was ≥1.80 (demonstrating DNA purity).

Quantification of bacterial 16S rRNA genes

To estimate total bacterial biomass per sample (16S rRNA gene copies per gram of wet stool), DNA extracted from the fecal collections was assessed via quantitative polymerase chain reaction (qPCR) based on previously published methods 87 , 88 . Briefly, all 20 μL qPCR reactions contained 10 uL of 2X SYBR Premix Ex Taq ™ (Tli RNase H Plus) (Takara Bio USA, Inc., San Jose, CA, USA), 0.3 μM (0.6 μL) of each primer (926 F: AAACTCAAAKGAATTGACGG; 1062 R: CTCACRRCACGAGCTGAC), 2 μL DNA template (or PCR-grade water as negative control), and 6.8 μL nuclease-free water (Thermo Fisher Scientific, Waltham, MA, USA). PCR thermal cycling conditions were as follows: 95 °C for 5 min, followed by 35 cycles of 95 °C for 15 s, 61.5 °C for 15 s, and 72 °C for 20 s, then hold at 72 °C for 5 min, along with a melt curve of 95 °C for 15 s, 60 °C for 1 min, then 95 °C for 1 s. Quantification was performed using a QuantStudio3™ Real-Time PCR System by Applied Biosystems with QuantStudio Design and Analysis Software 1.2 from Thermo Fisher Scientific (Waltham, MA, USA). All samples were analyzed in technical replicates. For quality assurance and quality control, molecular negative template controls (NTC) consisting of PCR-grade water (Invitrogen, Waltham, MA, USA) and positive controls created by linearized plasmids were run on every qPCR plate. Standard curves were run-in triplicate and used for sample quantification, ranging from 10 7 to 10 1 copies/μL with a cycle threshold (CT) detection limit cutoff of 33. Reaction efficiency was approximately 101%, with a slope of −3.29 and R 2  ≥ 0.99.

Fecal microbiome analysis

Amplification of the 16S rRNA gene sequence was completed in triplicate PCRs using 96-well plates. Barcoded universal forward 515 F primers and 806 R reverse primers containing Illumina adapter sequences, which target the highly conserved V4 region, were used to amplify microbial DNA 89 , 90 . PCR, amplicon cleaning, and quantification were performed as previously outlined 90 . Equimolar ratios of amplicons from individual samples were pooled together before sequencing on the Illumina platform (Illumina MiSeq instrument, Illumina, Inc., San Diego, CA). Raw Illumina microbial data were cleaned by removing short and long sequences, sequences with primer mismatches, uncorrectable barcodes, and ambiguous bases using the Quantitative Insights into Microbial Ecology 2 (QIIME2) software, version 2021.8 91 .

16S rRNA sequencing produced 7,366,128 reads with a median of 53,776 per sample (range: 9512–470,848). Paired-end, demultiplexed data were imported and analyzed using QIIME2 software. Upon examination of sequence quality plots, base pairs were trimmed at position 20 and truncated at position 240 and were run through DADA2 to remove low-quality regions and construct a feature table using ASVs. Next, the ASV feature table was passed through the feature-classifier plugin 92 , which was implemented using a naive Bayes machine-learning classifier, pre-trained to discern taxonomy mapped to the latest version of the rRNA database SILVA (138.1; 99% ASVs from 515 F/806 R region of sequences) 93 . Based on an assessment of alpha rarefaction, a threshold of 6500 sequences/sample was established, retaining all samples for downstream analysis. A phylogenic tree was then constructed using the fragment-insertion plugin with SILVA at a p-sampling depth of the rarefaction threshold to impute high-quality reads and normalize for uneven sequencing depth between samples 94 . Alpha diversity (intra-community diversity) was measured using observed ASVs and the Phylogenetic diversity index. Additionally, the Shannon index was calculated for the subgroup and case-study analyses to capture richness and evenness at the species level. Beta diversity (inter-community diversity) was measured using Bray-Curtis dissimilarity.

For shotgun metagenomics, DNA was sequenced on the Illumina NextSeq 500 platform (Illumina, CA, USA) to generate 2 × 150 bp paired-end reads at greater sequencing depth with a minimum of 10 million reads. Raw Illumina sequencing reads underwent standard quality control with FastQC. Adapters were trimmed using TrimGalore. DNA sequences were aligned to Hg38 using bowtie2 95 . DNA sequences were then analyzed via the bio bakery pipeline 96 for taxonomic composition and potential functional content with MetaPhlAn4 and HUMAnN 3.0 (UniRef90 gene-families and MetaCyc metabolic pathways), using standard parameters. Functional profiling resulted in 8528 distinct Kyoto Encyclopedia of Genes and Genomes Orthology (KO) groups and 511 metabolic pathways, which align with previous human gut microbiome studies 96 .

Blood sample collection and biochemical analyses

All participants were tested between the hours of 6:00 a.m. and 9:00 a.m., after an overnight fast for body composition assessments (height, body weight, and total body composition) at weeks 0, 4, and 8. 12-h fasted venous blood samples (~20 mL) were collected into EDTA-coated vacutainer tubes and centrifuged (Hettich Rotina 46R5) for 15 min at 4000 ×  g at −4 °C. After separation, plasma was stored at −80 °C until analyzed. Undiluted plasma samples were sent to Eve Technologies (Calgary, Alberta, Canada) for assessment of inflammatory cytokines [Granulocyte-macrophage colony-stimulating factor [GM-CSF], interferon-γ (IFNγ), interleukin (IL)-β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-17A, IL-23, and Tumor necrosis factor-α (TNFα)] using a high human sensitivity 14-plex cytokine assay (Millipore, Burlington, MA). Circulating LBP concentrations were quantified in duplicate using 1000x diluted plasma samples. A commercially available kit was used per the manufacturer’s protocol (Cat No. EH297RB, Thermo Fisher Scientific, Inc, Waltham, MA; intra-assay coefficient variation [CV] <10%).

Targeted plasma metabolomic analysis

For the plasma metabolomic analysis, a 12-h fasted venous blood sample (~20 mL) was collected into EDTA-coated vacutainer tubes and centrifuged (Hettich Rotina 46R5) for 15 min at 4000 ×  g at 4 °C. After separation, 2 mL of plasma was aliquoted and stored at −80 °C at the Biochemistry Laboratory at Skidmore College (Saratoga Springs, NY, USA). Samples were then sent to the Arizona Metabolomics Laboratory at ASU (Phoenix, AZ, USA) overnight on dry ice for analysis, where they were thawed at 4 °C and processed. Briefly, 50 μL of plasma from each sample was processed to precipitate proteins and extract metabolites by adding 500 μL MeOH and 50 μL internal standard solution (containing 1810.5 μM 13 C 3 -lactate and 142 μM 13 C 5 -glutamic acid). The mixture was vortexed (10 s) and stored for 30 min at –20 °C, then centrifuged at 224,000 ×  g for 10 min at 4 °C. Supernatants (450 μL) were extracted, transferred to new Eppendorf vials, and dried (CentriVap Concentrator; Labconco, Fort Scott, KS, USA). Samples were then reconstituted in 150 μL of 40% phosphate-buffered saline (PBS)/60% acetonitrile (ACN) and centrifuged again at 22,000 ×  g at 4 °C for 10 min. Supernatants (100 µL) were transferred to an LC autosampler vial for subsequent analysis. Quality control (QC) was performed by creating a pooled sample from all plasma samples and injecting once every ten experimental samples to monitor system performance.

The highly-reproducible targeted LC–MS/MS method used in the current investigation was modeled after previous studies 97 , 98 , 99 . The specific metabolites included in our targeted detection panel are representative of more than 35 biological pathways most essential to biological metabolism and have been successfully leveraged for the sensitive and broad detection of effects related to diet 100 , diseases 101 , drug treatment 102 , environmental contamination 103 , and lifestyle factors 104 . Briefly, LC–MS/MS experiments were performed on an Agilent 1290 UPLC-6490 QQQ-MS system (Santa Clara, CA, USA). Each sample was injected twice for analysis, 10 µL using negative and 4 µL using positive ionization modes. Chromatographic separations were performed in hydrophilic interaction chromatography (HILIC) mode on a Waters Xbridge BEH Amide column (150 × 2.1 mm, 2.5 µm particle size, Waters Corporation, Milford, MA, USA). The flow rate was 0.3 mL/min, the autosampler temperature was maintained at 4 °C, and the column compartment was set at 40 °C. The mobile phase system was composed of Solvents A (10 mM ammonium acetate, 10 mM ammonium hydroxide in 95% H 2 O/5% ACN) and B (10 mM ammonium acetate, 10 mM ammonium hydroxide in 95% ACN/5% H 2 O). After the initial 1 min isocratic elution of 90% Solvent B, the percentage of Solvent B decreased to 40% at t  = 11 min. The composition of Solvent B was maintained at 40% for 4 min ( t  = 15 min).

The mass spectrometer was equipped with an electrospray ionization (ESI) source. Targeted data acquisition was performed in multiple-reaction monitoring (MRM) mode. The LC–MS system was controlled by Agilent MassHunter Workstation software (Santa Clara, CA, USA), and extracted MRM peaks were integrated using Agilent MassHunter Quantitative Data Analysis software (Santa Clara, CA, USA).

GC–MS fecal short-chain fatty acid analysis

Before GC–MS analysis of SCFAs, frozen fecal samples were first thawed overnight under 4 °C. Then, 20 mg of each sample was homogenized with 5 μL hexanoic acid—6,6,6-d 3 (internal standard; 200 µM in H 2 O), 15 μL sodium hydroxide (NaOH [0.5 M]), and 500 μL MeOH. Samples were stored at −20 °C for 20 min and centrifuged at 22,000 ×  g for 10 min afterward. Next, 450 μL of supernatant was collected, and the sample pH was adjusted to 10 by adding 30 μL of NaOH:H 2 O (1:4, v-v). Samples were then dried, and the residues were initially derivatized with 40 µL of 20 mg/mL MeOX solution in pyridine under 60 °C for 90 min. Subsequently, 60 µL of MTBSTFA containing d 27 -mysristic acid was added, and the mixture was incubated at 60 °C for 30 min. The samples were then vortexed for 30 s and centrifuged at 22,000 ×  g for 10 min. Finally, 70 µL of supernatant was collected from each sample and injected into new glass vials for GC–MS analysis.

GC–MS conditions used here were adopted from a previously published protocol 105 . Briefly, GC–MS experiments were performed on an Agilent 7820 A GC-5977B MSD system (Santa Clara, CA); all samples were analyzed by injecting 1 µL of prepared samples. Helium was the carrier gas with a constant flow rate of 1.2 mL/min. Separation of metabolites was achieved using an Agilent HP-5 ms capillary column (30 m × 250 µm × 0.25 µm). Ramping parameters were as follows: column temperature was maintained at 60 °C for 1 min, increased at a rate of 10 °C/min to 325 °C, and then held at this temperature for 10 min. Mass spectral signals were recorded at an m/z range of 50–600, and data extraction was performed using Agilent Quantitative Analysis software. Following peak integration, metabolites were filtered for reliability. Only those with QC CV < 20% and a relative abundance of 1000 in > 80% of samples were retained for statistical analysis.

Untargeted fecal metabolomic analysis

Briefly, each fecal sample (~20 mg) was homogenized in 200 µL MeOH:PBS (4:1, v-v, containing 1810.5 μM 13 C 3 -lactate and 142 μM 13 C 5 -glutamic Acid) in an Eppendorf tube using a Bullet Blender homogenizer (Next Advance, Averill Park, NY). Then 800 µL MeOH:PBS (4:1, v-v, containing 1810.5 μM 13 C 3 -lactate and 142 μM 13 C 5 -glutamic Acid) was added, and after vortexing for 10 s, the samples were stored at −20 °C for 30 min. The samples were then sonicated in an ice bath for 30 min. The samples were centrifuged at 22,000 ×  g for 10 min (4 °C), and 800 µL supernatant was transferred to a new Eppendorf tube. The samples were then dried under vacuum using a CentriVap Concentrator (Labconco, Fort Scott, KS). Prior to MS analysis, the obtained residue was reconstituted in 150 μL 40% PBS/60% ACN. A quality control (QC) sample was pooled from all the study samples.

The untargeted LC–MS metabolomics method used here was modeled after that developed and used in a growing number of studies 106 , 107 , 108 . Briefly, all LC–MS experiments were performed on a Thermo Vanquish UPLC-Exploris 240 Orbitrap MS instrument (Waltham, MA). Each sample was injected twice, 10 µL for analysis using negative ionization mode and 4 µL for analysis using positive ionization mode. Both chromatographic separations were performed in hydrophilic interaction chromatography (HILIC) mode on a Waters XBridge BEH Amide column (150 × 2.1 mm, 2.5 µm particle size, Waters Corporation, Milford, MA). The flow rate was 0.3 mL/min, autosampler temperature was kept at 4 °C, and the column compartment was set at 40 °C. The mobile phase was composed of Solvents A (10 mM ammonium acetate, 10 mM ammonium hydroxide in 95% H 2 O/5% ACN) and B (10 mM ammonium acetate, 10 mM ammonium hydroxide in 95% ACN/5% H 2 O). After the initial 1 min isocratic elution of 90% B, the percentage of Solvent B decreased to 40% at t  = 11 min. The composition of Solvent B maintained at 40% for 4 min ( t  = 15 min), and then the percentage of B gradually went back to 90%, to prepare for the next injection. Using mass spectrometer equipped with an electrospray ionization (ESI) source, we collected untargeted data from 70 to 1050 m/z.

To identify peaks from the MS spectra, we made extensive use of the in-house chemical standards (~600 aqueous metabolites), and in addition, we searched the resulting MS spectra against the HMDB library, Lipidmap database, METLIN database, as well as commercial databases including mzCloud, Metabolika, and ChemSpider. The absolute intensity threshold for the MS data extraction was 1000, and the mass accuracy limit was set to 5 ppm. Identifications and annotations used available data for retention time (RT), exact mass (MS), MS/MS fragmentation pattern, and isotopic pattern. We used the Thermo Compound Discoverer 3.3 software for aqueous metabolomics data processing. The untargeted data were processed by the software for peak picking, alignment, and normalization. To improve rigor, only the signals/peaks with CV < 20% across quality control (QC) pools, and the signals showing up in >80% of all the samples were included for further analysis. To ensure the robustness of our model validation, we employed an enhanced validation approach by repeating the LOOCV process 100 times. Each iteration involves excluding one sample from the dataset to serve as the test set, with the model being trained on the remaining samples. This approach, referred to as ‘repeated LOOCV’, was adopted to mitigate bias and provide a thorough validation of our model’s predictive capability. The method signifies the number of repetitions of the LOOCV process, rather than splitting the dataset into 100 equal parts.

Multi-omics data analysis

For MOFA, bacterial 16S rRNA ASVs and plasma metabolites were integrated using the MOFA2 package 55 . Before integration, ASV sequences were filtered (minimum of 5 ASV in greater than 10% of all samples), collapsed to the genus level, and scaled using a centralized-log-ratio, as described previously 109 . Plasma metabolites were scaled and normalized as described in the metabolome analysis. The inputs for MOFA model training comprised 53 taxa and 138 metabolites. The latent factors and feature loadings were extracted from the best-trained model with the built-in functions of MOFA2. After model fitting, the number of factors was estimated by requiring a minimum of 2% variance explained across all microbiome modalities.

Integrating microbial taxa with the same filtration as stated above (at the genus level from 16S amplicon sequencing and species level from metagenomic sequencing) and cytokine data and fecal metabolomic data, respectively, was conducted with GFLASSO (R package: GFLASSO, v0.0.0.9000). This correlation-based network solution can handle multiple response variables for a given set of predictors (in this case: 1. cytokine abundances predicted by microbial taxa response; and 2. fecal metabolite response predicted by microbial taxa). Solution parsimony was determined by an unweighted (i.e., presence or absence of association by imposing a correlation threshold) network structure. The regularization and fusion parameters were determined from the smallest root mean squared error (RMSE) estimate via cross-validation, accounting for interdependencies among microbial features. The tested parameters encompassed all combinations between λ and γ with values ranging from 0 to 1 (inclusive) in step increments of 0.1. GFLASSO coefficient matrices were constructed using a threshold coefficient of >0.02 to discern the strongest associative signals.

Statistical analysis

Gastrointestinal symptom scores were on the low end of the GSRS scale and not normally distributed; therefore, nonparametric statistical tests were applied. Symptom prevalence (number of scores ≥ 2) and moderate symptom prevalence (≥4) for total, upper, and lower GI GSRS clusters were analyzed using contingency tables. Specifically, differences between IF-P and CR GI symptoms at baseline were compared using a Fisher’s Exact test, whereas baseline vs. weeks four and eight values were compared with McNemar’s test. Stool weight, BSS, fecal pH, plasma cytokines and LBP, and SCFAs were assessed for normality with Q-Q plots and Shapiro-Wilk tests and log-transformed where appropriate. These were then tested for time and interaction (group × time) effects using linear-mixed effect (LME) models, with each participant included as a random effect.

For analysis and visualization of the microbiome data, artifacts generated in QIIME2 were imported into the R environment (v4.2.2) using the phyloseq package (v1.42.0) 110 . Before conducting downstream analyses, sequences were filtered to remove all non-bacterial sequences, including archaea, mitochondria, and chloroplasts. After assessing normality (Shapiro-Wilk’s tests), LME models were used to test the effect of time and the interaction of group and time with the covariates of age and sex with each participant included as a random effect on the alpha diversity metrics using the nLME package (v3.1.160). For beta diversity, a nested permutational analysis of variance (PERMANOVA) was conducted on Bray-Curtis dissimilarities using the Adonis test in the vegan package (v2.6.2) with 999 permutations. The PERMANOVA model incorporated the factors of time, individual, interaction (group × time), and participant (nested factor). A permutation test for homogeneity in multivariate dispersion (PERMDISP) was conducted using the ‘betadisper’ function in the vegan package to compare dispersion. To support the Adonis analysis, intra-individual differences were also compared between groups, as previously described 111 , by calculating the within-subject distance for paired samples (baseline vs. weeks four and eight) and testing for group distances (Wilcoxon rank-sum test). Differential abundance analysis was performed using MaAsLin2 (v1.12.0) 18 . To detect changes in microbial features between groups over time, we built linear-mixed models that include group, time, and their interaction, with age and sex as covariates and the participant as a random factor. Before analysis, raw counts from the ASV table were filtered for any sequence not present five times in at least 30% of all samples. A significant p-value for the product term indicates that changes in microbial features differed over time between groups. The Benjamini–Hochberg (BH) procedure was used to correct for multiple testing at ≤0.10. To assess the correlation between changes in specific taxa and biomarkers over the eight-week intervention, Spearman correlation tests were performed.

Univariate and multivariate analyses of plasma metabolites and metabolic ontology analysis were performed, and results were visualized using the MetaboAnalystR 5.0 112 . Human metabolomic data were mapped to the Kyoto Encyclopedia of Genes and Genomes (KEGG) human pathway library to analyze predicted states 113 . The data were log 10 -transformed, and Pareto scaled to approximate normality before all analyses. A GLM was constructed with age, sex, and time as covariates to determine significantly affected metabolites by group intervention. Levene’s test was performed to detect significant homogeneity. The BH procedure was used to correct for multiple testing at ≤0.10. Fecal metabolomic analysis for the subgroup comparison was performed by assessing logFC values between groups with a Wilcoxon rank-sum test with BH adjustment. For pathway analysis, the impact was calculated using a hypergeometric test, while significance was determined using a test of relative betweenness centrality. Importantly, the BH procedure was not applied to pathway and enzyme enrichment analyses for the subgroup assessment since these analyses involve testing the significance of multiple related hypotheses rather than independent hypotheses, which is too conservative, resulting in false negative results.

For MOFA, latent factors explaining ≥2.0% of model variance from the plasma metabolomic and amplicon microbiome data were used to perform Spearman correlations on anthropometric and nutritional data and compared between IF-P and CR groups using Wilcoxon rank-sum tests. The highest beta coefficients (>0.3) detected from GFLASSO models were further assessed by performing Spearman correlations of select microbial features with the response variables (i.e., cytokines and fecal metabolites). All statistical tests were performed with a significance level of p  < 0.05 and BH correction of p .adj < 0.10. In addition, we present data in this study in accordance with the ‘Strengthening The Organization and Reporting of Microbiome Studies’ (STORMS) guidelines for human microbiome research 114 .

Reporting summary

Further information on research design is available in the  Nature Portfolio Reporting Summary linked to this article.

Data availability

The microbiome sequencing data generated in this study have been deposited in the BioProject Database of National Centre for Biotechnology Information database under accession code PRJNA847971 . The metadata data linking the microbiome sequences with the appropriate sample ID and intervention in this study are provided in Supplementary Data  1 . The processed data are available at https://github.com/Alex-E-Mohr/GM-Remodeling-IF-ProteinPacing-vs-CaloricRestriction .  Source data are provided with this paper.

Code availability

The R code used for analysis and figure generation for reproducibility purposes are available at: https://github.com/Alex-E-Mohr/GM-Remodeling-IF-ProteinPacing-vs-CaloricRestriction . 115

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Acknowledgements

We thank the trial volunteers for their dedication and commitment to the study protocol. We are grateful for the research assistants from Skidmore College who provided valuable assistance with study protocol design, scheduling, recruitment, data testing, collection, entry, and statistical analysis, and preparation of manuscripts: Molly Boyce, Jenny Zhang, Melissa Haas, Olivia Furlong, Emma Valdez, Jessica Centore, Annika Smith, Kaitlyn Judd, Aaliyah Yarde, Katy Ehnstrom, Dakembay Hoyte, Sheriden Beard, Heather Mak, and Monique Dudar. We are grateful for the extensive guidance and counseling provided by the registered dietitian Jaime Martin. We thank research coordinator Michelle Poe for her superior dedication to all aspects of the study. This study was primarily funded by an unrestricted grant from Isagenix International LLC to P.J.A. (grant #:1911-859), with secondary funding provided to K.L.S.

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Contributions

Study conceived and designed: P.J.A. Manuscript preparation with input from all authors: A.E.M., K.L.S., D.A.B., P.J., C.M.W., D.D.S., R.K.-B., H.G., J.K.-S., K.M.A., E.G., and P.J.A. Randomized study design and execution: K.M.A., and P.J.A. Microbiome analysis: A.E.M., D.A.B., C.M.W., and R.K.-B. Blood analyte analysis: A.E.M., K.L.S., and P.J.A. Metabolomic analysis: A.E.M., Y.J., H.G., and P.J. Statistical analysis and data presentation: A.E.M., C.M.W., D.D.S., R.K.-B., and P.J.A. Supervision and funding: K.L.S., E.G., and P.J.A.

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Competing interests.

P.J.A. is a consultant for Isagenix International LLC, the study’s sponsor, he is an advisory board member of the International Protein Board (iPB), and he receives financial compensation for books and keynote presentations on protein pacing ( www.paularciero.com ). Eric Gumpricht is employed by Isagenix International, LLC, the funding source for this research. Isagenix International, LLC had no role in the study design, data collection, analysis, or decision to publish. No authors have financial interests regarding the outcomes of this investigation. The other authors declare no competing interests.

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Mohr, A.E., Sweazea, K.L., Bowes, D.A. et al. Gut microbiome remodeling and metabolomic profile improves in response to protein pacing with intermittent fasting versus continuous caloric restriction. Nat Commun 15 , 4155 (2024). https://doi.org/10.1038/s41467-024-48355-5

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Published : 28 May 2024

DOI : https://doi.org/10.1038/s41467-024-48355-5

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