Open AccessProtein Intake to Maximize Whole-Body Anabolism during Postexercise Recovery in Resistance-Trained Men with High Habitual Intakes is Severalfold Greater than the Current Recommended Dietary Allowance
Author(s) -
Michael Mazzulla,
Sidney Abou Sawan,
Eric Williamson,
Sarkis J. Hannaian,
Kimberly A. Volterman,
Daniel W. D. West,
Daniel R. Moore
Publication year - 2020
Publication title -
the journal of nutrition/the journal of nutrition
Language(s) - English
Resource type - Journals
eISSN - 1541-6100
pISSN - 0022-3166
DOI - 10.1093/jn/nxz249
Subject(s) - anabolism , phenylalanine , protein metabolism , endocrinology , protein catabolism , creatinine , chemistry , medicine , urea , protein degradation , ingestion , amino acid , nitrogen balance , urine , excretion , catabolism , zoology , metabolism , biochemistry , biology , organic chemistry , nitrogen
Background Dietary protein supports resistance exercise–induced anabolism primarily via the stimulation of protein synthesis rates. The indicator amino acid oxidation (IAAO) technique provides a noninvasive estimate of the protein intake that maximizes whole-body protein synthesis rates and net protein balance. Objective We utilized IAAO to determine the maximal anabolic response to postexercise protein ingestion in resistance-trained men. Methods Seven resistance-trained men (mean ± SD age 24 ± 3 y; weight 80 ± 9 kg; 11 ± 5% body fat; habitual protein intake 2.3 ± 0.6 g·kg−1·d−1) performed a bout of whole-body resistance exercise prior to ingesting hourly mixed meals, which provided a variable amount of protein (0.20–3.00 g·kg−1·d−1) as crystalline amino acids modeled after egg protein. Steady-state protein kinetics were modeled with oral l-[1-13C]-phenylalanine. Breath and urine samples were taken at isotopic steady state to determine phenylalanine flux (PheRa), phenylalanine excretion (F13CO2; reciprocal of protein synthesis), and net balance (protein synthesis − PheRa). Total amino acid oxidation was estimated from the ratio of urinary urea and creatinine. Results Mixed model biphasic linear regression revealed a plateau in F13CO2 (mean: 2.00; 95% CI: 1.62, 2.38 g protein·kg−1·d−1) (r2 = 0.64; P ˂ 0.01) and in net balance (mean: 2.01; 95% CI: 1.44, 2.57 g protein·kg−1·d−1) (r2 = 0.63; P ˂ 0.01). Ratios of urinary urea and creatinine concentrations increased linearly (r = 0.84; P ˂ 0.01) across the range of protein intakes. Conclusions A breakpoint protein intake of ∼2.0 g·kg−1·d−1, which maximized whole-body anabolism in resistance-trained men after exercise, is greater than previous IAAO-derived estimates for nonexercising men and is at the upper range of current general protein recommendations for athletes. The capacity to enhance whole-body net balance may be greater than previously suggested to maximize muscle protein synthesis in resistance-trained athletes accustomed to a high habitual protein intake. This trial was registered at clinicaltrials.gov as NCT03696264.