What is the question?

• The question is: What is the relationship between dietary patterns consumed and risk of type 2 diabetes? The population of interest included infants and young children up to age 24 months, children and adolescents, and adults and older adults.

Why was this question asked?

• This systematic review was conducted by the 2025 Dietary Guidelines Advisory Committee as part of the process to develop the Dietary Guidelines for Americans, 2025-2030.

How was this question answered?

• The Committee conducted a systematic review to answer this question with support from the USDA Nutrition Evidence Systematic Review team. This review updated existing systematic reviews that were conducted by the 2020 Dietary Guidelines Advisory Committee and as part of the Dietary Patterns Systematic Reviews Project.

What is the answer to the question?

• A conclusion statement cannot be drawn about the relationship between dietary patterns consumed by children and adolescents and risk of type 2 diabetes because of substantial concerns with directness.
• Dietary patterns consumed by adults and older adults that are characterized by higher intakes of vegetables, fruits, whole grains, legumes, nuts, and fish/seafood and lower intakes of red and processed meats, high-fat dairy products, refined grains, and sugar-sweetened foods and beverages are associated with lower risk of type 2 diabetes. This conclusion statement is based on evidence graded as strong.

How up-to-date is this systematic review?

• Conclusion statements from this review are based on articles published between January 1980 and May 2023.

Background

• This systematic review was conducted by the 2025 Dietary Guidelines Advisory Committee as part of the process to develop the Dietary Guidelines for Americans, 2025-2030. The U.S. Departments of Health and Human Services (HHS) and Agriculture (USDA) appointed the 2025 Dietary Guidelines Advisory Committee (Committee) in January 2023 to review evidence on high priority scientific questions related to diet and health. Their review forms the basis of their independent, science-based advice and recommendations to HHS and USDA, which is considered as the Departments develop the next edition of the Dietary Guidelines. As part of that process, the Committee conducted a systematic review with support from the USDA Nutrition Evidence Systematic Review (NESR) team to answer the following question: What is the relationship between dietary patterns consumed and risk of type 2 diabetes? This is an update to existing systematic reviews that were conducted by the 2020 Dietary Guidelines Advisory Committee and as part of the Dietary Patterns Systematic Reviews Project.

Methods

• The Committee conducted a systematic review using the methodology of the USDA NESR team. The Committee first developed a protocol. The intervention/exposure and comparators for all populations were consumption of a dietary pattern compared to a different dietary pattern and different adherence to/consumption levels of a dietary pattern. The outcomes were measures of risk of type 2 diabetes in all populations. Additional criteria were established to include: a) randomized or non-randomized controlled trial, prospective or retrospective cohort, or nested case-control designs, b) published in English in peer-reviewed journals, c) studies in countries classified as high or very high on the Human Development Index, and d) participants with a range of health statuses. The review excluded studies that exclusively enrolled participants who were being treated for a disease.
• NESR librarians performed the literature search in PubMed, Embase, CINAHL, and Cochrane to identify articles published between October 2019 and May 2023 in children and adolescents and between January 2014 and May 2023 in adults and older adults. Two NESR analysts independently screened all electronic results and the reference lists of included articles based on the pre-determined criteria. The results of this search were combined with eligible included articles from the existing reviews.
• NESR analysts extracted data, from each included article, with a second analyst verifying accuracy of the extraction. Two NESR analysts independently conducted a formal risk of bias assessment, by study design, for each included article, then reconciled any differences in the assessment. The Committee qualitatively synthesized evidence from all included articles in the updated literature search and existing systematic reviews according to the synthesis plan, with attention to the overarching themes or key concepts from the findings, similarities and differences between studies, and factors that may have affected the results. The Committee developed conclusion statements by starting with the conclusion from the existing review and determining whether and what updates were needed based on the newly published evidence. After establishing the need for updating the review, the Committee then developed conclusion statements and graded the strength of evidence based on its consistency, precision, risk of bias, directness and generalizability.

Results

Children and Adolescents

Conclusion statement and grade

• A conclusion statement cannot be drawn about the relationship between dietary patterns consumed by children and adolescents and risk of type 2 diabetes because of substantial concerns with directness. (Grade Not Assignable)

Summary of the evidence

• The body of evidence includes 15 articles (1 randomized controlled trial; 14 from prospective cohort studies) published since 2019 that met inclusion for this review in children and adolescents and were assessed as they relate to the evidence included in the existing review (1 article).
• The 2025 Committee was not able to draw a conclusion due to critical limitations in the body of evidence.

Adults and Older Adults

Conclusion statement and grade

• Dietary patterns consumed by adults and older adults that are characterized by higher intakes of vegetables, fruits, whole grains, legumes, nuts, and fish/seafood and lower intakes of red and processed meats, high-fat dairy products, refined grains, and sugar-sweetened foods and beverages are associated with lower risk of type 2 diabetes. This conclusion statement is based on evidence graded as strong. (Grade: Strong)

Summary of the evidence

• The body of evidence includes 118 articles (14 articles from randomized controlled trials; 104 articles from prospective cohort studies) published since 2014 that met inclusion for this review in adults and older adults and were assessed as they relate to the evidence included in the existing review (37 articles).
• The direction and effect size of results were similar across studies.
• The sizes of study groups were adequate or large and variation around effect estimates was narrow across studies.
• Most studies were designed and conducted well, although there were some concerns for outcome measurement in some studies.
• The populations, dietary patterns, and outcome measures examined directly represented those of interest in the review.
• The evidence applies to the U.S. population

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Suggested citation: Talegawkar S, Tobias D, Fung T, Giovannucci E, Hoelscher DM, Anderson CAM, Booth S, Deierlein A, Gardner C, Raynor H, Stanford FC, Taylor C, English LK, Reigh, N, Higgins M, Butera G, Callahan E, Huang, S, Raghavan R, Terry N, Obbagy J. Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review. November 2024. U.S. Department of Agriculture, Food and Nutrition Service, Center for Nutrition Policy and Promotion, Nutrition Evidence Systematic Review. Available at: https://doi.org/10.52570/NESR.DGAC2025.SR12