What is the question?

• The question is: What is the relationship between dietary patterns consumed and risk of breast cancer? The populations of interest for this question included infants, young children, children, adolescents, 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 an existing review that was conducted by 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 and nuts, and whole grains and lower intakes of red and processed meats, refined grains, and sugar-sweetened foods and beverages are associated with lower risk of postmenopausal breast cancer relative to other dietary patterns. The data regarding dietary patterns and risk of premenopausal breast cancer point in the same direction, but the evidence is less consistent. This conclusion statement is based on postmenopausal breast cancer evidence graded as moderate.  

How up-to-date is this systematic review?

• Conclusion statements from this review are based on articles published between January 2000 and January 2024.
   

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 breast cancer? 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 or exposure was dietary patterns consumed by infants, young children, children, adolescents, adults, and older adults, the comparators were different dietary patterns or different levels of adherence to/consumption of the same dietary pattern, and the outcome included incident cases of breast cancer. 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 exclusively enrolled participants who were being treated for a disease.
• NESR librarians conducted a literature search in PubMed, Embase, and Cochrane to identify articles published between January 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 according to the synthesis plan, 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 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 breast cancer

Conclusion statement and grade

• Dietary patterns consumed by adults and older adults that are characterized by higher intakes of vegetables, fruits, legumes and nuts, and whole grains and lower intakes of red and processed meats, refined grains, and sugar-sweetened foods and beverages are associated with lower risk of postmenopausal breast cancer relative to other dietary patterns. The data regarding dietary patterns and risk of premenopausal breast cancer point in the same direction, but the evidence is less consistent. This conclusion statement is based on postmenopausal breast cancer evidence graded as moderate. (Grade: Moderate)

Summary of the evidence

• This body of evidence includes 26 articles (1 from randomized controlled trials, 24 from prospective cohort studies and 1 from a nested case-control study) published since January 2020 that met the inclusion criteria for this review and were assessed as they relate to the evidence included in the existing review (52 articles).
• The direction of results was similar across studies, but effect size differed.
• The size of study groups was small in some studies. Variation around the effect estimates ranged from narrow to wide across studies.
• Some studies were designed and conducted well.
• The populations, dietary patterns, comparators, and outcomes that were examined directly represent those of interest in this review.
• The evidence applies to the U.S. population but may not represent all racial and ethnic groups.

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Suggested citation: Fung T, Giovannucci E, Anderson CAM, Booth S, Deierlein A, Gardner C, Hoelscher DM, Raynor H, Stanford FC, Talegawkar S, Taylor C, Tobias D, Callahan EH, English LK, Higgins M, Huang S, Reigh N, Butera G, Terry N, Obbagy J. Dietary Patterns and Risk of Breast Cancer: A Systematic Review. U.S. Department of Agriculture, Food and Nutrition Service, Center for Nutrition Policy and Promotion, Nutrition Evidence Systematic Review; 2024. https://doi.org/10.52570/NESR.DGAC2025.SR21