Increased intake of fiber and starchy foods has been recommended in the treatment or prevention of a range of diseases including dumping syndrome, hyperlipidemia, gallstones, diabetes, Crohn's disease, constipation, irritable bowel, diverticular disease, and colonic cancer. The nature and physiological effects of fiber are diverse. However in general, insoluble fibers increase fecal bulk and decrease transit time. On the other hand, soluble fibers have metabolic effects secondary to reducing the rate of small intestinal absorption. In the colon, along with undigested starch, they are largely fermented yielding short-chain fatty acids which may have further metabolic effects. At present although much further work is required, the clinical management of hyperlipidemia, diabetes, constipation, and diverticular disease have already been significantly influenced as a result of the ideas and experimental evidence generated by the fiber hypothesis.