Prevention of colon carcinogenesis by components of dietary fiber

Cancer of rite colon is one of the lending causes of cancer death in Wester n countries and is increasing rapidly in Japan. Epidemiological and laborat ory animal madel studies have suggested an inverse relationship between col on cancer risk and intake of fiber-rich foods. The protective effect of die tary fiber which comprises a heterogeneous group of nonstarch polysaccharid es such as cellulose, hemicellulose, and pectin and noncarbohydrate substan ces such as phytic acid depends on the nature and source of fiber in the di et. Laboratory animal madels have consistently shown that dietary administr ation of wheat bran reduced colon tumarigenesis. Human diet intervention st udies have demonstrated that supplemental wheat bran in the diet decreased the formation of putative metabolites such as secondary bile acids and diac ylglycerol in the color? that have been shown to act as tumor promoters in the colon. Among the components of dietary fiber, especially wheat bran, ph ytic acid (inositol hexaphosphate) has been studied extensively for its che mopreventive properties against colon carcinogenesis in the laboratory anim al models. In studies carried out to date, dietary phytic acid reduced the incidence of colonic aberrant crypt foci, putative preneoplastic lesions in rats. Oral administration of phytic acid was shown to inhibit colon carcin ogenesis in rodents during the initiation and postinitiation stages. These studies provide evidence for potential chemopreventive properties of phytic acid against colon cancer. With regard to mode of action, phytic acid acts as an antioxidant, to reduce the rate of cell proliferation and to augment the immune response by enhancing the activity of natural killer (NK) cells .