Lifestyle risk factors with strong evidence include lack of exercise, cigarette smoking, alcohol, and obesity The risk of colon cancer can be reduced by maintaining a normal body weight through a combination of sufficient exercise and eating a healthy diet.

Starting in the 1970s, dietary recommendations to prevent colorectal cancer often included increasing the consumption of whole grains, fruits and vegetables, and reducing the intake of red meat and processed meats. This was based on animal studies and retrospective observational studies.

However, large scale prospective studies have failed to demonstrate a significant protective effect, and due to the multiple causes of cancer and the complexity of studying correlations between diet and health, it is uncertain whether any specific dietary interventions (outside of eating a healthy diet) will have significant protective effects In 2018 the National Cancer Institute stated that "There is no reliable evidence that a diet started in adulthood that is low in fat and meat and high in fiber, fruits, and vegetables reduces the risk of CRC by a clinically important degree.

With regard to dietary fiber, the 2014 World Health Organization cancer report noted that it has been hypothesized that fiber might help prevent colorectal cancer, but most studies have not borne this out, and status of the science remained unclear as of 2014.

A 2019 review, however, found evidence of benefit from dietary fiber and whole grains. The World Cancer Research Fund listed the benefit of fiber for prevention of colorectal cancer as "probable" as of 2017.

Higher physical activity is recommended Physical exercise is associated with a modest reduction in colon but not rectal cancer risk. High levels of physical activity reduce the risk of colon cancer by about 21%. Sitting regularly for prolonged periods is associated with higher mortality from colon cancer. The risk is not negated by regular exercise, though it is lowered