The controversy over the amount and timing of protein intake to support anabolic responses to resistance exercise persists. The literature provides evidence of a range of required amounts to support recovery from resistance exercise and the deposition of lean body mass.
A relatively recent technique to estimate amino acid requirements, called the indicator amino acid oxidation (IAAO) method, makes addressing this problem easier, but has resulted in requirements that are even higher than prior derived values. The existing work using this technique had been conducted on non-training days, meaning that the amount of dietary protein needed to support repair and growth on training days remains unknown. Mazzulla and colleagues addressed this question in a study they report in the March 2020 issue of The Journal of Nutrition.
The study involved resistance-trained men (n = 7) with elevated normal daily protein intakes of 2.3 g/kg. The subjects were provided 8 hourly meals containing a mix of amino acids designed to reflect egg protein levels after performing a bout of whole body exercise. The meals contained between 0.20 and 3.00 g/kg protein and each subject participated in 6 different metabolic trials. Breath and urine samples were collected to determine protein synthesis, net balance, and total amino acid oxidation using the marker amino acid, phenylalanine.
The breakpoint in protein intake that maximized whole body anabolism after exercise in these resistance exercise trained men was 2.0 g/kg-1/d-1. The authors concluded that it may be possible to further enhance whole body net balance and muscle protein synthesis in resistance trained athletes that are normally consuming a high protein diet.
In a commentary on this article, Reidy discusses several aspects of the study design or physiological responses that could have contributed to this much higher protein requirement. In closing the commentary, Reidy proposes a question of whether the elevated requirement reflects an increased demand by hypertrophy of visceral organs like liver and the intestine.
Commentary provided by: Reidy PT. Muscle or nothing! Where is the excess protein going in men with high protein intakes engaged in strength training? J Nut 2020; 150(3): 505-11.