Background: Coingestion of protein and/or free amino acids with carbohydrate has been reported to accelerate postexercise muscle glycogen synthesis due to an increase in the insulin response.
Purpose: To determine the extent to which the combined ingestion of carbohydrate and a casein protein hydrolysate with or without additional free leucine can increase insulin levels during postexercise recovery in endurance-trained athletes. To determine how this affects whole-body plasma glucose disposal during postexercise recovery.
Methods: Fourteen male athletes (age: 24.3 ± 0.8 yr; V̇O2max: 62.9 ± 1.4 mL·kg−1·min−1) were subjected to three randomized crossover trials in which they performed 2 h of exercise (55% Wmax). Thereafter, subjects were studied for 3.5 h during which they ingested carbohydrate (CHO: 0.8 g·kg−1·h−1), carbohydrate and a protein hydrolysate (CHO-PRO: 0.8 and 0.4 g·kg−1·h−1, respectively), or carbohydrate, a protein hydrolysate, and free leucine (CHO-PRO-LEU: 0.8, 0.4, and 0.1 g·kg−1·h−1, respectively) in a double-blind fashion. Continuous infusions with [6,6-2H2] glucose were applied to quantify plasma glucose appearance (Ra) and disappearance rates (Rd).
Results: Plasma insulin responses were 108 ± 17 and 190 ± 33% greater in the CHO-PRO and CHO-PRO-LEU trial, respectively, compared with the CHO-trial (P < 0.01). Plasma glucose responses were lower in the CHO-PRO and CHO-PRO-LEU trial compared with the CHO-trial (35 ± 5 and 42 ± 11% lower, respectively; P < 0.01). Plasma glucose Ra and Rd were greater in the CHO versus the CHO-PRO and CHO-PRO-LEU trials (P < 0.05). Glucose Rd represented 100 ± 0.03% of Ra in all trials.
Conclusions: The combined ingestion of a protein hydrolysate and/or free leucine with carbohydrate (0.8 g·kg−1·h−1) substantially augments insulin secretion, but does not affect plasma glucose disposal during the first 3.5 h of postexercise recovery in trained athletes.