Microbial Fermentation of Starch: Its Impact on the Range of Acceptable Carbohydrate Intake

Starch, a major source of carbohydrates in human nutrition, is extensively hydrolyzed in the gastrointestinal tract of children and adults. A small fraction of the ingested starch reaches the cecum and colon where it is fermented by the gut microbiome into short-chain fatty acids (SCFA) and other products. Recent data in humans and in animal models have demonstrated the extensive effects of short-chain fatty acids on whole body energy metabolism, appetite, insulin resistance, fatty acid oxidation, fat accretion, obesity, and diabetes. Clear discernible effects of SCFA on the rates of production of glucose, its oxidation and uptake in the fasting state were, however, not observed. In the fed state, the effects on glucose metabolism are related to the effects of SCFA on insulin sensitivity, possibly the consequence of their influence on lipid metabolism. The suggested limits of carbohydrate intake were based upon the kinetics and metabolism of glucose in the basal state and on the responses to glucose administration. It is postulated that in healthy subjects, the present data do not suggest any significant impact of microbial fermentation of starch on the range of acceptable intake of carbohydrates.