Dietary Patterns and Colorectal Cancer Risk: Global Cancer Update Programme (CUP Global) Systematic Literature Review

Background: The 2018 World Cancer Research Fund/American Institute for Cancer Research Third Expert Report, including studies up to 2015, determined limited–no conclusion evidence on dietary patterns and colorectal cancer (CRC) risk due to insufficient data and varying pattern definitions. Objectives: This updated review synthesized literature on dietary patterns and CRC risk/mortality. Methods: PubMed and Embase were searched through 31 March, 2023, for randomized controlled trials (RCTs) and prospective cohort studies on adulthood dietary patterns. Patterns were categorized by derivation method: a priori, a posteriori, or hybrid, and were then descriptively reviewed in relation to the primary outcomes: CRC risk or mortality. The Global Cancer Update Programme Expert Committee and Expert Panel independently graded the evidence on the likelihood of causality using predefined criteria. Results: Thirty-two dietary scores from 53 observational studies and 3 RCTs were reviewed. Limited–suggestive evidence was concluded for higher alignment with a priori–derived patterns: Mediterranean, healthful plant-based index, Healthy Eating Index (HEI)/alternate HEI, and Dietary Approaches to Stop Hypertension (DASH), in relation to lower CRC risk. Common features across these diets included high plant-based food intake and limited red/processed meat. Hybrid-derived patterns: the empirical dietary index for hyperinsulinemia (EDIH) and the empirical dietary inflammatory pattern (EDIP), showed strong–probable evidence for increased CRC risk. Evidence for a priori–derived low-fat dietary interventions and a posteriori–derived patterns was graded as limited–no conclusion. By cancer subsite, higher alignment with Mediterranean diet showed limited–suggestive evidence for lower rectal cancer risk, and that with HEI/alternate HEI and DASH showed limited–suggestive evidence for lower colon and rectal cancer risks. EDIH and EDIP showed strong–probable evidence for increased colon cancer risks. All exposure–mortality pairs and other pattern–outcome associations were graded as limited–no conclusion. Conclusions: This review highlights the role of dietary patterns in CRC risk/mortality, providing insights for future research and public health strategies. This review was registered at PROSPERO as CRD42022324327 (https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022324327).