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.
Branchedchain 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.
Smith, Montain, and Young are with the Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA. Anderson is with Natick Soldier Research, Development and Engineering Center, Natick, MA.