The aim of this systematic review and meta-analysis was to summarize the evidence on the relationship between intake of 12 major food groups, including whole grains, refined grains, vegetables, fruit, nuts, legumes, eggs, dairy, fish, red meat, processed meat and sugar-sweetened beverages with risk of colorectal cancer (CRC). We conducted a systematic search in PubMed and Embase for prospective studies investigating the association between these 12 food groups and risk of CRC until April 2017. Summary risk ratios (RRs) and 95% confidence intervals (95% CI) were estimated using a random effects model for high vs. low intake categories, as well as for linear and nonlinear relationships. An inverse association was observed for whole grains (RR : 0.95, 95% CI 0.93, 0.97; n = 9 studies), vegetables (RR : 0.97, 95% CI 0.96, 0.98; n = 15), fruit (RR : 0.97, 95% CI 0.95, 0.99; n = 16) and dairy (RR : 0.93, 95% CI 0.91, 0.94; n = 15), while a positive association for red meat (RR : 1.12, 95% CI 1.06, 1.19; n = 21) and processed meat (RR : 1.17, 95% CI 1.10, 1.23; n = 16), was seen in the linear dose-response meta-analysis. Some evidence for nonlinear relationships was observed between vegetables, fruit and dairy and risk of colorectal cancer. Findings of this meta-analysis showed that a diet characterized by high intake of whole grains, vegetables, fruit and dairy products and low amounts of red meat and processed meat was associated with lower risk of CRC.
