Mechanisms of action of β-glucan in postprandial glucose metabolism in healthy men

Objective: To assess whether beta -glucan (which is fermented in the colon) lowers postprandial glucose concentrations through mechanisms distinct from a delayed carbohydrate absorption and inhibits de novo lipogenesis. Design: Administration of frequent small meals each hour over 9 h allows a rate of intestinal absorption to be reached which is independent of a delayed absorption. A group of 10 healthy men received either an isoenergetic diet containing 8.9 g/day beta -glucan or without beta -glucan for 3 days. On the third day, the diet was administered as fractioned meals ingested every hour for 3 h. Setting: Laboratory for human metabolic investigations. Subjects: Ten healthy male volunteers. Main outcome measures: Plasma glucose and insulin concentrations, glucose kinetics, glucose oxidation, de novo lipogenesis. Results: On the third day, plasma glucose and free fatty acid concentrations, carbohydrate and lipid oxidation, and energy expenditure were identical with beta -glucan and cellulose. Plasma insulin concentrations were, however, 26% lower with beta -glucan during the last 2 h of the 9 h meal ingestion. Glucose rate of appearance at steady state was 12% lower with beta -glucan. This corresponded to a 21% reduction in the systemic appearance rate of exogenous carbohydrate with beta -glucan, while endogenous glucose production was similar with both diets. De novo lipogenesis was similar with and without beta -glucan. Conclusion: Administration of frequent meals with or without beta -glucan results in similar carbohydrate and lipid metabolism. This suggests that the lowered postprandial glucose concentrations which are observed after ingestion of a single meal containing beta -glucan are essentially due to a delayed and somewhat reduced carbohydrate absorption from the gut and do not result from the effects of fermentation products in the colon.