Changes in diet from ancient times until the present are described. Previously relatively low in energy and animal products yet high in fibre-containing foods, diets are now high in energy and animal products (particularly fat), yet contain less fibre. The changing incidences of bowel disorders and diseases are described, with assessments of the role of diet. Clearly, diet is implicated as regards predisposition to constipation, appendicitis, colorectal cancer and diverticular disease; however, a meaningful dietary role in irritable bowel syndrome, ulcerative colitis and Crohn's disease is doubtful. In South Africa the rarity of bowel diseases in rural blacks compared with whites affords valuable aetiological information about some bowel diseases. The low occurrence thereof (except inflammatory bowel disease) in Indian and coloured populations is not readily explicable. While dietary changes in whites are being widely urged in order to combat degenerative diseases, the magnitude of changes made is unlikely to reduce the occurrence of bowel diseases. The progressive westernization of the diets and lifestyles of less-privileged populations is likely to be associated with increases in the incidences of these diseases.