An association between a vegetarian diet and a lower risk of developing cancer has been found in several observational studies. Specifically, some studies report a decreased incidence of colorectal cancer,[1][2][3][4] gastric cancer,[5][6], and prostate cancer.[1][6] However, other studies have found that a vegetarian diet did not alter the prevalence of colorectal, breast, or prostate cancer.[7]
These findings are not definitive, and other factors that are not accounted for in the observational studies will significantly affect these results. For example, the lower cancer risk could be because people who choose to eat vegetarian diets tend to be more active and are less likely to smoke cigarettes.[8]