Passage of starch into the colon of humans: quantitation and implications

It has been suggested that a significant amount of starch may reach the colon undigested and stimulate microbial fermentation. Indirect estimates of the quantity of starch reaching the colon have been obtained from breath hydrogen (H2) measurements, but numerous variables, i.e., dietary fiber source and level of intake, oral hygiene, hyperventilation, and cigarette smoking, stimulate H2 production and may exaggerate estimates of starch malabsorption. With proper controls, however, the lactulose breath H2 test based on total excess volume seems to provide a reasonable measure of the average amount of starch metabolized in the colon. Direct estimates of starch metabolism from human ileostomy studies suggest that typically less than 5% of the ingested starch escapes digestion in the small intestine. The general assumption that starch malabsorption stimulates normal colonic function, particularly with respect to colorectal carcinogenesis, is not entirely supported by the limited number of available epidemiologic studies. Further experimental studies are needed to elucidate the role of starch intake and malabsorption on colonic function and human health issues.