What is the question?

• The question is: What is the relationship between dietary patterns consumed and risk of cognitive decline, dementia, Alzheimer's disease, and mild cognitive impairment? The population of interest for this question included children and adolescents, and adults and older adults at intervention/exposure, and adults and older adults at outcome.

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 an existing review that was conducted by the Dietary Patterns Subcommittee of the 2020 Dietary Guidelines Advisory Committee.

What is the answer to the question?

• Dietary patterns consumed by adults and older adults that are characterized by higher intakes of vegetables, fruits, legumes or beans, nuts, fish and/or seafood, and unsaturated vegetable oils/fats and lower in red and processed meats and sugar-sweetened beverages, are associated with lower risk of age-related cognitive decline, mild cognitive impairment, dementia and/or Alzheimer's disease. This conclusion statement is based on evidence graded as moderate.

How up-to-date is this systematic review?

• The conclusion statement from this review is based on articles published between March 2020 and January 2024, as well as studies that were excluded from prior reviews but met the updated inclusion criteria.  

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 USDA’s Nutrition Evidence Systematic Review (NESR) team to answer the following question: What is the relationship between dietary patterns and risk of cognitive decline, dementia, Alzheimer’s disease, and mild cognitive impairment? This review is an update to an existing review that was conducted by the 2020 Dietary Guidelines Advisory Committee.

Methods

• The Committee conducted a systematic review using the methodology of the USDA NESR team. The Committee first developed a protocol. The intervention/exposure was consumption of a dietary pattern in children and adolescents, and adults and older adults, the comparator was consumption of a different dietary pattern or different adherence/consumption levels to the same dietary pattern, and the outcomes were measures of cognitive decline, dementia, Alzheimer’s disease, and mild cognitive impairment. Additional inclusion criteria were established for the following study characteristics: a) use randomized or non-randomized controlled trial, prospective or retrospective cohort, or nested case-control study designs, b) be published in English in peer-reviewed journals, c) be from countries classified as high or very high on the Human Development Index, and d) enroll participants with a range of health statuses. The review excluded studies that did not control for any of the key confounders identified in the analytic framework, interventions with a length <12 weeks, or interventions that included <30 participants per study group for between-subject analyses and did not provide a power calculation indicating that the study was appropriately powered for the outcomes of interest.
• NESR librarians conducted a literature search in PubMed, Embase, and Cochrane to identify articles published between March 2020 and January 2024.  Two NESR analysts independently screened all electronic results and the reference lists of included articles based on the pre-determined criteria.
• 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 the evidence, with attention given 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 a conclusion statement and graded the strength of evidence based on its consistency, precision, risk of bias, directness and generalizability. The Committee developed a conclusion statement 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 graded the strength of evidence for the conclusion statement based on its consistency, precision, risk of bias, directness and generalizability

Results

Dietary patterns and risk of cognitive decline, dementia, Alzheimer's disease, and mild cognitive impairment

Conclusion statement and grade

• Dietary patterns consumed by adults and older adults that are characterized by higher intakes of vegetables, fruits, legumes or beans, nuts, fish and/or seafood, and unsaturated vegetable oils/fats and lower in red and processed meats and sugar-sweetened beverages, are associated with lower risk of age-related cognitive decline, mild cognitive impairment, dementia and/or Alzheimer's disease. This conclusion statement is based on evidence graded as moderate. (Grade: Moderate)

Summary of the evidence

• Eighty-three articles met inclusion for this review, including 1 randomized controlled trial, 1 nested case-control study, and 81 prospective cohort studies.
• The direction of results was similar across studies, but effect size differed.
• The sizes of study groups were adequate or large, though confidence intervals ranged from narrow to wide across studies.
• Some studies were designed and conducted well, though many were at high or very high risk of bias.
• The populations, interventions/exposures, and comparators that were examined directly represent those of interest in this review, but there were concerns with the directness of outcome assessment.
• The dietary patterns, outcomes, and participant characteristics are applicable to the U.S. population.

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Suggested citation: Booth S, Talegawkar S, Fung T, Hoelscher DM, Anderson CAM, Deierlein A, Gardner C, Giovannucci E, Raynor H, Stanford FC, Taylor C, Tobias D, Reigh N, English LK, Higgins M, Butera G, Terry N, Obbagy J. Dietary Patterns and Risk of Cognitive Decline, Dementia, Alzheimer's Disease, and Mild Cognitive Impairment: 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.SR20