Plasma amino acid responses after consumption of beverages with varying protein type

To examine how different proteins in a carbohydrate-protein beverage affect postprandial amino acid (AA), glucose, and insulin responses.

Two randomized, repeated-measures experiments were performed. In one, 10 volunteers drank 3 carbohydrate-protein beverages (380 kcal, 76 g carbohydrate, 19 g protein, 2 g fat) in separate (>7 days) trials, each differing in protein type. All drinks consisted of cocoa (4 g) and nonfat dry milk (1 g) supplemented with casein (CAS), whey (WP), or a casein and whey blend (CAS-WP). Ten additional volunteers consumed the same drinks after 60 min of varying-intensity exercise (60% and 85% VO2peak). Blood glucose, insulin, glucose-dependent insulinotrophic polypeptide (GIP), and AAs were measured every 15-30 min for 4 hr after beverage consumption.

Branched-chain AA concentrations peaked at 30 min and did not differ between beverages at rest (0.69 +/- 0.12 mmol/L) or postexercise (0.70 +/- 0.07 mmol/L). There were no significant differences between beverages with respect to initial (time 0-60) or total area under the curve (time 0-240) for any outcome measures at rest or postexercise.

High-carbohydrate beverages containing various proportions of milk proteins procured from a supplier to the commercial industry had no impact on AA concentration. Retrospective chemical analysis of commercial proteins showed that casein was partially hydrolyzed; therefore, consumers should carefully consider the manufacturer (to ensure that the product contains intact protein) or other factors (i.e., cost or taste) when procuring these beverages for their purported physiological effects.