A diet rich in fruits, whole grains and vegetables appears to lower the risk of many cancers, including colon cancer. Vegetables most likely to help prevent colon cancer are broccoli, cabbage, cauliflower, kale and other members of the cruciferous family. A diet rich in produce may be beneficial, in part, because these foods tend to be high in folate, a B vitamin. But research on folate has been inconsistent, especially regarding supplements (folic acid is the form used in supplements and in fortified foods).
A high-fiber diet helps prevent constipation, and the theory was that this might reduce exposure of the intestinal wall to carcinogens. But several large studies have failed to find a protective effect for fiber. And there’s no known link between constipation and colon cancer. The Women’s Health Initiative did not find that a high fiber intake reduced colon cancer risk. Still, another large study did find that a very high intake of fiber was protective. Fiber is hard to study—it isn’t just one compound but many.
A high-fat diet, particularly one high in animal fats and red meats, has been blamed for increasing colon cancer risk, but the jury is still out. Dietary fat, in itself, is no longer regarded as a factor in colon cancer. If red meats do increase the risk—and some evidence suggests they do—it may be because they are often cooked at high temperatures, so that potential cancer-promoting chemicals are formed. In any event, there are other reasons, such as heart health, to avoid a diet high in animal fats. Consuming omega-3 fats from fish, on the other hand, may reduce the risk of colon cancer, though the evidence is preliminary.
Calcium and vitamin D may reduce the risk of colon cancer, whether you get them from food or supplements, by reducing precancerous polyps. A 2008 review article in Nutrition Research Reviews found that a high intake of dairy products, especially milk, was also associated with a reduced risk of colon cancer, perhaps because of their calcium, vitamin D, and other nutrients. And according to a 10-year AARP study in 2009, people who get the most calcium from dairy products and supplements are 20 percent less likely to develop colon cancer than those with a low intake.
Magnesium-rich foods may reduce the risk of colon cancer, research in the American Journal of Clinical Nutrition suggested in 2012. The study found this potential benefit only in overweight or obese people and those over 55. In the analysis, which included data from nine previous studies, each 100-milligram daily increase in dietary magnesium was associated with a 12 percent lower risk of colon cancer. That’s the amount in 4 ounces of fish, a cup of beans, 2 ounces of peanuts or half a cup of cooked spinach. Most previous studies have had similar findings.
People who drink at least four cups of coffee (regular or decaf) a day are 15 percent less likely to develop colon cancer over a decade than nondrinkers, according to an analysis from the NIH/AARP Diet and Health Study of people age 50 to 71, in the American Journal of Clinical Nutrition in 2012. Decaf also seemed to reduce the risk of rectal cancer; tea had no effect at all. Previous studies have been inconsistent; different coffee types and methods of preparation may have different effects on cancer risk.
• Don’t smoke: Tobacco is a major risk factor for colon cancer.
• Discuss aspirin, including low-dose aspirin, with your health care provider, especially if you have a family history of colon cancer or have had prior polyps. Many studies have found that long-term aspirin use, even at low doses, reduces the risk. Since aspirin can cause gastrointestinal bleeding and ulcers, get medical advice before taking it.
• Exercise regularly, and lose weight if you’re overweight. Even in moderate amounts, exercise appears to be protective.
• Get screened via colonoscopy, sigmoidoscopy or annual stool tests.