Current athlete-specific protein recommendations are based almost exclusively on research in males.
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.
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·kg−1·d−1) as crystalline amino acids modeled after egg protein, with constant phenylalanine (30.5 mg·kg−1·d−1) and excess tyrosine (40.0 mg·kg−1·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 [13C] phenylalanine ingestion. Total protein oxidation was estimated from the urinary urea–creatinine ratio (U/Cr).
A mixed model biphase linear regression revealed a break point (i.e., estimated average requirement) of 1.49 ± 0.44 g·kg−1·d−1 (mean ± 95% confidence interval) in Ox (r2 = 0.64) and 1.53 ± 0.32 g·kg−1·d−1 in NB (r2 = 0.65), indicating a saturation in whole-body anabolism. U/Cr increased linearly with protein intake (r2 = 0.56, P < 0.01).
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 ~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·kg−1·d−1).
Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, CANADA
Address for Correspondence: Daniel R. Moore, Ph.D., Faculty of Kinesiology and Physical Education, University of Toronto, 100 Devonshire Place Toronto, ON, Canada M5S 2C9; E-mail: firstname.lastname@example.org.
Submitted for publication July 2018.
Accepted for publication October 2018.