Carbohydrate fermentation decreases hepatic glucose output in healthy subjects

Abstract

Fermentation of undigested carbohydrate produces short-chain fatty acids (SCFA), some of which have been shown to reduce hepatic glucose production (HGP) in animals. The aim of this study was to examine whether carbohydrate fermentation decreases HGP in man. Ten healthy subjects consumed 90-g carbohydrate portions of either brown rice or barley for dinner in random order 1 week apart. The following morning, glucose kinetics were measured basally and during an oral glucose tolerance test (OGTT). HGP was calculated as the difference between the total rate of glucose appearance (calculated from % enrichment of 6,6 dideuterated glucose [6,6 D 2 glucose]) and the rate of appearance of gut-derived glucose (calculated from 6- 3H glucose in the glucose drink). To detect fermentation, breath H 2 content was measured by end-expiratory sampling of alveolar air. Significantly more breath H 2 was produced after barley consumption (24 ± 4 v 4 ± 1 ppm, P < .001), indicating that barley contains more fermentable carbohydrate than rice. Glucose tolerance improved after the barley meal, with the peak OGTT plasma glucose concentration being 0.7 mmol/L lower than that after the rice meal (7.7 ± 0.4 v 8.4 ± 0.3 mmol/L, P < .05). This was primarily due to a 30% reduction in HGP (area under the curve, 909 ± 116 v 1,295 ± 157 μmol/kg; P < .01). No difference in the rates of glucose disappearance or gut glucose absorption was observed. However, serum free fatty acid (FFA) concentrations were significantly reduced the morning after the barley meal. In summary, carbohydrate fermentation enhances the suppression of HGP and FFA levels by oral glucose in man. Fermentation of carbohydrate may therefore play a role in improving postprandial glycemia after high-fiber, high-carbohydrate diets.