A 2015 study found vegetarians had significantly lower rates of colon and colorectal cancers than non-vegetarians. Published in JAMA, the study looked at data from 77,659 people participating in The Adventist Health Study 2, which was designed to investigate the generally healthy habits of Adventist followers and to address a variety of questions about diet and nutrition. Researchers categorized the participants into five groups according to their diet: vegans who abstained from all animal products; lacto-ovo-vegetarians who ate eggs and/or dairy; pescatarians who ate fish and seafood but avoided other meats; semi-vegetarians who ate meat less than once weekly; and non-vegetarians who ate meat at least once weekly. After tracking the participants for around seven years, and taking into account various lifestyle factors, the researchers discovered:
Vegetarian diets were associated with a 22% reduced risk of colorectal cancer compared with non-vegetarian diets.
Pescatarian diets were associated with the greatest reduction (43%) in colorectal cancer risk, followed by lacto-ovo-vegetarian (18%), vegan (16%), and semi-vegetarian (8%) diets.
These findings are of potential public health importance—colorectal cancer is the second leading cause of cancer death in the US. In addition, even though the study was only observational and therefore can’t prove a cause-and-effect relationship, it is consistent with past research which has shown associations between eating red meat and higher risks of colorectal cancer, and between eating fiber-rich foods and lower risks of colorectal cancer.