Nobody knows exactly what causes colon cancer.
But the latest news about prevention is encouraging. Here are some good bets, plus a few educated guesses and theories. A healthy diet, on the other hand, is high in vegetables, fruits, and whole grains, and low in animal fats. Eating large amounts of fat may be unhealthy for the colon. Some fat passes into the colon undigested, and the bacteria there act upon the fat, producing potentially carcinogenic substances that may damage the colon lining.