Co-ingestion of carbohydrate with protein does not further augment post-exercise muscle protein synthesis

The present study was designed to assess the impact of co-ingestion of various amounts of carbohydrate combined to an ample amount of protein intake on post-exercise muscle protein synthesis rates. Ten healthy, fit men (20+/-0.3 y) were randomly assigned to 3 cross-over experiments. After 60 min of resistance exercise, subjects consumed 0.3 g.kg(-1).h(-1) protein hydrolysate with 0, 0.15, or 0.6 g.kg(-1).h(-1) carbohydrate during a 6 h recovery period (PRO, PRO+LCHO, and PRO+HCHO, respectively). Primed, continuous infusions with L-[ring-(13)C6]phenylalanine, L-[ring-(2)H2]tyrosine, and [6,6-(2)H2]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 post-exercise recovery. Plasma insulin responses were significantly greater in PRO+HCHO compared to PRO+LCHO and PRO (18.4+/-2.9 vs. 3.7+/-0.5 and 1.5+/-0.2 U.6h.L(-1), respectively: P<0.001). Plasma glucose rate of appearance (Ra) and disappearance (Rd) increased over time in PRO+HCHO and PRO+LCHO but not in PRO. Plasma glucose Ra and Rd 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 FSR did not differ between treatments and averaged 0.10+/-0.01, 0.10+/-0.01 and 0.11+/-0.01 %.h(-1) in the PRO, PRO+LCHO and PRO+HCHO experiments, respectively. In conclusion, co-ingestion of carbohydrate during recovery does not further stimulate post-exercise muscle protein synthesis when ample protein is ingested. Key words: resistance exercise, muscle, protein metabolism, nutrition, recovery.