Increased Protein Requirements in Female Athletes after Variable-Intensity Exercise.

Purpose: Protein requirements are primarily studied in the context of resistance or endurance exercise with little research devoted to variable-intensity intermittent exercise characteristic of many team sports. Further, female populations are underrepresented in dietary sports science studies. We aimed to determine a dietary protein requirement in active females performing variable-intensity intermittent exercise using the indicator amino acid oxidation (IAAO) method. We hypothesized that these requirements would be greater than current IAAO-derived estimates in non-active adult males. Methods: Six females (21.2 +/- 0.8 y, 68.8 +/- 4.1 kg, 47.1 +/- 1.2 ml O2[dot operator]kg-1[dot operator]min-1; mean +/- SE) completed 5-7 metabolic trials during the luteal phase of the menstrual cycle. Participants performed a modified Loughborough Intermittent Shuttle Test prior to consuming 8 hourly mixed meals providing the test protein intake (0.2-2.66 g[dot operator]kg-1[dot operator]d-1), 6 g[dot operator]kg-1[dot operator]d-1 carbohydrate, and sufficient energy for resting and exercise-induced energy expenditure. Protein was provided as crystalline amino acids modeling egg protein with [13C]phenylalanine as the indicator amino acid. Phenylalanine turnover (Q) was determined from urinary [13C]phenylalanine enrichment. Breath 13CO2 excretion (F13CO2) was analyzed using mixed effects bi-phase linear regression with the breakpoint and upper 95% CI approximating the estimated average requirement (EAR) and recommended dietary allowance (RDA), respectively. Results: Protein intake had no effect on Q (68.7 +/- 7.3 [mu]mol[dot operator]kg-1[dot operator]h-1; mean +/- SE). F13CO2 displayed a robust bi-phase response (R2 = 0.66) with an EAR of 1.41 g[dot operator]kg-1[dot operator]d-1and RDA of 1.71 g[dot operator]kg-1[dot operator]d-1. Conclusions: The protein requirement estimate of 1.41and 1.71 g[dot operator]kg-1[dot operator]d-1 for females performing variable-intensity intermittent exercise is greater than the IAAO-derived estimates of adult males (0.93 and 1.2 g[dot operator]kg-1[dot operator]d-1) and at the upper range of the ACSM athlete recommendations (1.2-2.0 g[dot operator]kg-1[dot operator]d-1). (C) 2017 American College of Sports Medicine

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