Short-chain fatty acids and human colonic function: Roles of resistant starch and nonstarch polysaccharides

Resistant starch (RS) is starch and products of its small intestinal digest ion that enter the large bowel. It occurs for various reasons including che mical structure, cooking of food, chemical modification, and food masticati on. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; m ajor components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and f luid and electrolyte uptake. Butyrate is a preferred substrate for colonocy tes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic ferment ation in humans is difficult, and indirect measures (e.g., fecal samples) o r animal models have been used. Of the latter, rodents appear to be of limi ted value, and pigs or dogs are preferable. RS is less effective than NSP i n stool bulking, but epidemiological data suggest that it is more protectiv e against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The con tribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical proc edure that accommodates the major influences on RS means this is yet to be established.