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The present study was designed to assess the impact of coingestion of various amounts of carbohydrate combined with an ample amount of protein intake on postexercise muscle protein synthesis rates. Ten healthy, fit men (20 +/- 0.3 yr) were randomly assigned to three crossover experiments. After 60 min of resistance exercise, subjects consumed 0.3 g x kg(-1) x h(-1) protein hydrolysate with 0, 0.15, or 0.6 g x kg(-1) x h(-1) carbohydrate during a 6-h recovery period (PRO, PRO + LCHO, and PRO + HCHO, respectively). Primed, continuous infusions with L-ring-(13)C(6)phenylalanine, L-ring-(2)H(2)tyrosine, and 6,6-(2)H(2)glucose were applied, and blood and muscle samples were collected to assess whole body protein turnover and glucose kinetics as well as protein fractional synthesis rate (FSR) in the vastus lateralis muscle over 6 h of postexercise recovery. Plasma insulin responses were significantly greater in PRO + HCHO compared with PRO + LCHO and PRO (18.4 +/- 2.9 vs. 3.7 +/- 0.5 and 1.5 +/- 0.2 U.6 h(-1) x l(-1), respectively, P < 0.001). Plasma glucose rate of appearance (R(a)) and disappearance (R(d)) increased over time in PRO + HCHO and PRO + LCHO, but not in PRO. Plasma glucose R(a) and R(d) were substantially greater in PRO + HCHO vs. both PRO and PRO + LCHO (P < 0.01). Whole body protein breakdown, synthesis, and oxidation rates, as well as whole body protein balance, did not differ between experiments. Mixed muscle protein FSR did not differ between treatments and averaged 0.10 +/- 0.01, 0.10 +/- 0.01, and 0.11 +/- 0.01%/h in the PRO, PRO + LCHO, and PRO + HCHO experiments, respectively. In conclusion, coingestion of carbohydrate during recovery does not further stimulate postexercise muscle protein synthesis when ample protein is ingested.
Koopman et al. (Wed,) studied this question.