Protein to Maximize Whole-Body Anabolism in Resistance-trained Females after Exercise.

Introduction Current athlete-specific protein recommendations are based almost exclusively on research in males. Purpose Using the minimally invasive indicator amino acid oxidation technique, we determined the daily protein intake that maximizes whole-body protein synthesis (PS) and net protein balance (NB) after exercise in strength-trained females. Methods Eight resistance-trained females (23 +/- 3.5 yr, 67.0 +/- 7.7 kg, 163.3 +/- 3.7 cm, 24.4% +/- 6.9% body fat; mean +/- SD) completed a 2-d controlled diet during the luteal phase before performing an acute bout of whole-body resistance exercise. During recovery, participants consumed eight hourly meals providing a randomized test protein intake (0.2-2.9 g center dot kg(-1)center dot d(-1)) as crystalline amino acids modeled after egg protein, with constant phenylalanine (30.5 mg center dot kg(-1)center dot d(-1)) and excess tyrosine (40.0 mg center dot kg(-1)center dot d(-1)) intakes. Steady-state whole-body phenylalanine rate of appearance (Ra), oxidation (Ox; the reciprocal of PS), and NB (PS - Ra) were determined from oral [C-13] phenylalanine ingestion. Total protein oxidation was estimated from the urinary urea-creatinine ratio (U/Cr). Results A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 +/- 0.44 g center dot kg(-1)center dot d(-1) (mean +/- 95% confidence interval) in Ox (r(2) = 0.64) and 1.53 +/- 0.32 g center dot kg(-1)center dot d(-1) in NB (r(2) = 0.65), indicating a saturation in whole-body anabolism. U/Cr increased linearly with protein intake (r(2) = 0.56, P < 0.01). Conclusions Findings from this investigation indicate that the safe protein intake (upper 95% confidence interval) to maximize anabolism and minimize protein oxidation for strength-trained females during the early similar to 8-h postexercise recovery period is at the upper end of the recommendations of the American College of Sports Medicine for athletes (i.e., 1.2-2.0 g center dot kg(-1)center dot d(-1)).