Co-ingestion Of Carbohydrate With Protein Does Not Stimulate Post-exercise Muscle Protein Synthesis Rates

Endurance athletes maximize post-exercise muscle glycogen synthesis by ingesting ample amounts of carbohydrate following exercise. In contrast, resistance athletes generally focus on protein intake during recovery to augment muscle protein anabolism. It has been suggested that both carbohydrate and protein should be ingested to maximize muscle protein synthesis rates. As many recreational athletes perform resistance type exercise for health and/or esthetic purposes, they generally prefer to restrict their caloric intake during recovery. Therefore, it is of importance to assess the need for co-ingestion of carbohydrate with protein on post-exercise muscle protein synthesis. PURPOSE: To determine the impact of the co-ingestion of different amounts of carbohydrate with protein on post-exercise muscle protein synthesis. METHODS: Ten healthy, untrained men were randomly assigned to 3 randomized cross-over trials. 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 of L-[ring-13C6]phenylalanine, L-[ring-2H2]tyrosine, and [6,6-2H2]glucose were applied, and blood and muscle samples were collected to assess whole-body protein turnover, glucose kinetics and fractional synthetic rate (FSR) in the vastus lateralis muscle over 6 h of recovery. RESULTS: Plasma insulin response was significantly higher in HCHO+PRO compared to LCHO+PRO 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 HCHO+PRO and LCHO+PRO but not in PRO. Plasma glucose Ra and Rd were substantially greater in HCHO+PRO vs. LCHO+PRO (P<0.01). Whole-body protein breakdown, synthesis and oxidation rates, as well as whole-body protein balance did not differ between trials. In accordance mixed muscle FSR did not differ between trials and averaged 0.114±0.010, 0.104±0.009% and 0.100±0.009%·h-1 in the HCHO+PRO, LCHO+PRO and PRO trial, respectively (NS). CONCLUSIONS: Co-ingestion of carbohydrate with an ample amount of protein hydrolysate (0.3 g·kg-1·h-1) does not further augment muscle protein synthesis rate during post-exercise recovery.