Dietary inflammatory index and risk of major digestive tract cancers: a GRADE-assessed systematic review and dose-response meta-analysis

Gastrointestinal (GI) cancers are an umbrella term for a group of malignant tumors that affect the digestive system. This systematic review and meta-analysis aimed to evaluate the association between the Dietary Inflammatory Index (DII) and the risk of GI cancers by synthesizing evidence from observational studies. PubMed, Scopus, and Web of Science were searched using terms related to GI cancers and DII. A total of 52 observational studies (18 cohort, 34 case-control) were analyzed. Random or fixed effects meta-analyses were conducted to pool risk ratio (RR) for the highest vs. the lowest DII categories, with dose-response analyses performed where feasible. Quality was assessed via the Risk of Bias in Non-randomised Studies of Exposures tool. Evidence certainty was graded using the GRADE framework. Higher DII scores (pro-inflammatory diets) were significantly associated with increased risks of colorectal (RR 1.16, 95% confidence interval [CI] 1.04–1.29), colon (RR 1.12, 95% CI 1.11–1.33), and rectal cancers (RR 1.25, 95% CI 1.07–1.47) in cohort studies. No significant associations were found for gastric or pancreatic cancers in cohort studies. Case-control studies showed stronger associations for oral (RR 2.46), esophageal (RR 2.63), and pancreatic cancers (RR 2.57). The findings highlight the importance of dietary modifications to reduce inflammation for cancer prevention. Further prospective studies are needed to clarify causal relationships and refine dietary recommendations. PROSPERO registration no. CRD42023484691.