Nuts and legumes consumption and risk of colorectal cancer: a systematic review and meta-analysis

Several case–control and prospective cohort studies have examined the association between the consumption of nuts and legumes and the risk of colorectal cancer. For the quantitative assessment of this association, we conducted a meta-analysis of observational studies. We searched PubMed and Web of Science databases along with hand searches for eligible studies published up to January 2022. A total of 13 studies (8 cohort studies and 5 case–control studies) on nuts consumption and 29 studies (16 cohort studies and 13 case–control studies) on legumes consumption were included in the meta-analysis. The pooled relative risks (RRs) of colorectal cancer for the highest versus lowest categories of nuts consumption and legumes consumption were 0.84 (95% CI: 0.71–0.99) and 0.90 (95% CI: 0.83–0.98), respectively. Based on the dose–response analysis, a 28 g/day (1 serving/day) increment of nut consumption was associated with a 33% lower risk of colorectal cancer, and 100 g/day (1 serving/day) increment of legumes consumption was associated with a 21% lower risk of colorectal cancer. By geographic region for nuts consumption, however, the inverse association for the highest versus lowest categories was only observed in Asia (RR = 0.44; 95% CI: 0.29–0.68) from 3 studies, and no association was found in America (RR = 1.01; 95% CI: 0.92–1.11) (P_difference = 0.003) or Europe (RR = 1.02; 95% CI: 0.84–1.25) (P_difference = 0.003). In addition, the associations tended to be weak when stratified by adjustment for confounders. Our findings suggest that the evidence for an association is currently weak, and thus further well-designed prospective studies are needed.