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/displayᵣecord. php? ID=CRD42022324327).