Starch and dietary fibre: their physiological and epidemiological interrelationships.

Until the 1980s, starch in the human diet was assumed to be totally degraded and absorbed in the small intestine. Several lines of evidence since then have indicated that this is not the case, including studies of factors controlling stool output, stool bulk on elemental diets, epidemiological studies of starch intakes in developed versus developing nations, and indications using breath hydrogen that fermentation takes place in the large intestine when starch is fed. Of the few direct estimations of starch escaping absorption in the small intestine that have been carried out, one has been conducted using intubation of healthy volunteers, where two different starch meals were fed and samples aspirated from the terminal ileum. This study demonstrated that 8-10% starch escaped absorption on average, with subjects varying from 2 to 20%. Hence a sizeable proportion of starch consumed daily may reach the large intestine, with important physiological consequences. Neither small intestinal transit time nor volume of flow were related to the extent of starch malabsorption in this study. However, many factors may play a role in the extent of malabsorption, and research is continuing to investigate physiological and food characteristics that may influence the digestion and absorption of starch.