Most of the serious organic diseases of the colon are etiologically linked to the high-saturated-fat and low-fiber Western diet. Benign but common conditions, such as appendicitis and diverticular disease of the colon, appear to be due to deficiency of fiber and attendant low-bulk stools. Colon cancer appears to be due to carcinogens created in the colon itself. Contributing to carcinogen production are cocarcinogens in bile and an increase in anaerobic bacteria, both directly related to high levels of saturated fat in the diet. If these common disorders of the colon are to be controlled, our diet will require major modification. Changes will have to include reduction of saturated fats of animal origin and increase in cereal grains.