Mechanistic Insights Into Postprandial Insulin–Glucagon Interactions and Their Impact on Glucose Flux After Protein–Glucose Coingestion in Humans

Despite stimulating glucagon secretion, the addition of protein to carbohydrate typically lowers postprandial glucose excursions. The mechanisms underlying this phenomenon are incompletely understood. In healthy young adults, using the triple stable isotope glucose tracer technique, we investigated how whey protein and glucose coingestion modulates postprandial glucose fluxes. Despite stimulating glucagon secretion and impairing suppression of endogenous glucose production, whey protein-glucose coingestion significantly reduced glycemic excursions. Although whey protein-glucose coingestion strongly enhanced the insulin and glucose-dependent insulinotropic polypeptide (but not glucagon-like peptide 1) responses, whole-body glucose uptake was not enhanced; rather, the net glycemic benefit seemed to stem from reduced early-phase glucose absorption.