The Relationship Between Plant-Based Diet and Risk of Digestive System Cancers: A Meta-Analysis Based on 3,059,009 Subjects

Background and Objectives Diets containing red or processed meat are associated with a growing risk of digestive system cancers. Whether a plant-based diet is protective against cancer needs a high level of statistical evidence. Methods We performed a meta-analysis of five English databases, including PubMed, Medline, Embase, Web of Science databases, and Scopus, on October 24, 2021 to identify published papers. Cohort studies or case-control studies that reported a relationship between plant-based diets and cancers of the digestive system were included. Summary effect-size estimates are expressed as Risk ratios (RRs) or Odds ratios (ORs) with 95% confidence intervals and were evaluated using random-effect models. The inconsistency index (I 2) and τ 2 (Tau 2) index were used to quantify the magnitude of heterogeneity derived from the random-effects Mantel-Haenszel model. Results The same results were found in cohort (adjusted RR = 0. 82, 95% CI: 0. 78–0. 86, P 0. 001, I 2 = 46. 4%, Tau 2 = 0. 017) and case-control (adjusted OR = 0. 70, 95% CI: 0. 64–0. 77, P 0. 001, I 2 = 83. 8%, Tau 2 = 0. 160) studies. The overall analysis concluded that plant-based diets played a protective role in the risk of digestive system neoplasms. Subgroup analyses demonstrated that the plant-based diets reduced the risk of cancers, especially pancreatic (adjusted RR = 0. 71, 95% CI: 0. 59–0. 86, P 0. 001, I 2 = 55. 1%, Tau 2 = 0. 028), colorectal (adjusted RR = 0. 76, 95% CI: 0. 69–0. 83, P 0. 001, I 2 = 53. 4%, Tau 2 = 0. 023), rectal (adjusted RR = 0. 84, 95% CI: 0. 78–0. 91, P 0. 001, I 2 = 1. 6%, Tau 2 = 0. 005) and colon (adjusted RR = 0. 88, 95% CI: 0. 82–0. 95, P 0. 001, I 2 = 0. 0%, Tau 2 = 0. 000) cancers, in cohort studies. The correlation between vegan and other plant-based diets was compared using Z-tests, and the results showed no difference. Conclusions Plant-based diets were protective against cancers of the digestive system, with no significant differences between different types of cancer. Systematic Review Registration https: //www. crd. york. ac. uk/prospero/displayᵣecord. php? ID=CRD42022322276, Identifier: CRD42022322276.