BACKGROUND: Muscle protein synthesis (MPS) is regulated by essential amino acid (EAA) intake, postprandial extracellular EAA concentrations, and exercise. During energy balance, consuming approximately 0.10-0.14 g EAA/kg/meal (0.25-0.30 g protein/kg/meal) optimally stimulates MPS after exercise. However, EAA requirements are increased during energy deficit, and whether consuming EAA beyond 0.10-0.14 g/kg/meal further stimulates MPS during energy deficit is unknown.
PURPOSE: Determine the effects of standard and high EAA intake on resting and post-resistance exercise MPS during moderate energy deficit.
METHODS: Nineteen males (mean±SD; age: 22.9±5y; BMI: 25.4±2.7kg/m²) completed a randomized, double-blind crossover study consisting of two, 5d periods of controlled energy deficit (30±4%), separated by a 14d washout. At the end of each energy deficit period, MPS was determined at rest (postabsorptive and postprandial) and post-resistance exercise (postprandial) using a unilateral resistance exercise model and primed, constant ²H₅-phenylalanine infusions. Drinks providing standard (0.10g/kg/meal, 7.87±0.87g) and high (0.30g/kg/meal, 23.5±2.54g) EAA amounts were consumed post-exercise. Circulating EAA concentrations were measured throughout each infusion.
RESULTS: Postabsorptive MPS at rest was not different (p=0.71) between standard (0.047±0.3%/h) and high (0.045±0.02%/h). In the postprandial state, and independent of EAA, MPS at rest (standard, 0.055±0.01%/h; high, 0.061±0.02%/h) and post-exercise (standard, 0.055±0.01%/h; high, 0.065±0.02%/h) was greater than postabsorptive MPS at rest (fed state main effect, p=0.019 and p=0.005). Postprandial MPS at rest and post-exercise did not differ (p=1.0). EAA concentrations were greater in high (peak: 2915±569µmol/L; AUC: 228485±54783µmol/L/240min) than standard (peak: 1843±497µmol/L; AUC: 75727±32254µmol/L/240min; both, p=0.001).
CONCLUSION: Despite greater increases in extracellular EAA concentrations for high versus standard EAA intakes and the mechanical stimulus exerted by exercise, the stimulatory effect of varying doses of free-form EAA on MPS are equivalent during moderate energy deficit.
Supported by USAMRDC; authors’ views not official U.S. Army or DoD policy