ABSTRACT
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 colorectal cancer? This review is an update to existing reviews 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
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, fried potatoes,
saturated fat, and sugar-sweetened foods and beverages are associated with lower risk of colon and rectal cancer. Some of these dietary patterns also included fish, low-fat dairy, tea and coffee. This conclusion statement is based on evidence graded as moderate.
(Grade: Moderate)
Summary of the evidence:
• This body of evidence includes 29 articles (27 from prospective cohort studies and 2 from nested case-control studies) published
since January 2020 that met inclusion criteria for this review and were assessed as they related to the evidence included in the
existing review (46 articles).
• The direction of results and size of effects were similar across studies.
• 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.