Diet, nutrition, and cancer. The role of fiber.

The mechanisms by which dietary fiber could inhibit development of colon cancer include effects on fecal weight and transit time, adsorption of bile acids, dilution of colonic contents, production of short chain fatty acids (products of fiber fermentation), inhibition of dehydroxylation of bile acids, and regulation of energy intake. Review of the literature suggests that effects on fecal weight and transit time and adsorption of bile acids are not likely mechanisms. Since concentration of bile acids is lower in feces of less susceptible populations, dilution of colonic contents may contribute to fiber effects. High colonic pH is associated with promotion of cancer and production of short chain fatty acids would counteract this effect. Animals maintained on calorie-restricted diets exhibit fewer spontaneous or experimentally induced tumors. Regulation of energy intake by fiber may contribute towards reduction of colon cancer incidence in man especially when caloric content is low from infancy.