Low-dose acarbose does not delay digestion of starch but reduces its bioavailability

Aims Slowly digestible starch is associated with beneficial health effects. The glucose-lowering drug acarbose has the potential to retard starch digestion since it inhibits alpha-amylase and alpha-glucosidases. We tested the hypothesis that a low dose of acarbose delays the rate of digestion of rapidly digestible starch without reducing its bioavailability and thereby increasing resistant starch flux into the colon.

Methods In a crossover study, seven healthy males ingested corn pasta (50.3 g dry weight), naturally enriched with C-13, with and without 12.5 mg acarbose. Plasma glucose and insulin concentrations, and (CO2)-C-13 and hydrogen excretion in breath were monitored for 6 h after ingestion of the test meals. Using a primed continuous infusion of D-[6,6-H-2(2)] glucose, the rate of appearance of starch-derived glucose was estimated, reflecting intestinal glucose absorption.

Results Areas under the 2-h postprandial curves of plasma glucose and insulin concentrations were significantly decreased by acarbose (-58.1 +/- 8.2% and -72.7 +/- 7.4%, respectively). Acarbose reduced the overall 6-h appearance of exogenous glucose (bioavailability) by 22 +/- 7% (mean +/- SE) and the 6-h cumulative (CO2)-C-13 excretion by 30 +/- 6%.

Conclusions These data show that in healthy volunteers a low dose of 12.5 mg acarbose decreases the appearance of starch-derived glucose substantially. Reduced bioavailability seems to contribute to this decrease to a greater extent than delay of digestion. This implies that the treatment effect of acarbose could in part be ascribed to the metabolic effects of colonic starch fermentation.