B-24C Free Communication/Slide Protein Supplementation and Athletes
Protein metabolism during endurance exercise is characterized by increased protein breakdown, the degree of which influences protein synthesis postexercise. Exogenous provision of amino acids impacts this relationship.
To determine whether postexercise mixed muscle protein fractional synthetic rate (FSR) differs in response to habitual consumption of dietary protein in excess of the RDA.
Male runners (n=5, 21 yrs, 71 kg, 9% body fat, 180 cm, VO2peak 70 ml/kg/min) participated in a randomized, crossover design diet intervention, where they consumed either a low (0.8 g/kg; LP), moderate (1.8 g/kg; MP), or high (3.6 g/kg; HP) protein diet for 4 weeks. Diets were eucaloric, and carbohydrate, fat and protein approximated 60%, 30%, 10%; 55%, 30%, 15; and 40%, 30%, 30% for LP, MP, and HP respectively. Nitrogen balance was determined following 3 weeks of the intervention. At week 4, a primed continuous infusion of [2H5] phenylalanine (2 μmol/kg; 0.05 μmol/kg/min) was used to assess FSR following a 75 min run at 70% VO2peak.
Nitrogen balance remained positive for all dietary interventions, with significant increases (p < 0.05) with each increase in the level of dietary protein. FSR for both LP (0.083 %h) and MP (0.078 %h) were greater (p < 0.05) than HP (0.052 %h) following exercise. There was no difference in FSR between LP and MP.
Habitual consumption of a high protein diet significantly decreased FSR in runners postexercise further establishing a role for dietary protein in the regulation of skeletal muscle protein metabolism. Further research is needed to better define the relationship between dietary protein intake and optimal protein utilization in endurance runners. Supported in part by NCBA and UCRF.