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 nonactive adult males.
Methods: Six females (21.2 ± 0.8 yr, 68.8 ± 4.1 kg, 47.1 ± 1.2 mL O2·kg−1·min−1; mean ± SE) completed five to seven metabolic trials during the luteal phase of the menstrual cycle. Participants performed a modified Loughborough Intermittent Shuttle Test before consuming eight hourly mixed meals providing the test protein intake (0.2–2.66 g·kg−1·d−1), 6 g·kg−1·d−1 CHO and sufficient energy for resting and exercise-induced energy expenditure. Protein was provided as crystalline amino acid 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 biphase linear regression with the breakpoint and upper 95% confidence interval approximating the estimated average requirement and recommended dietary allowance, respectively.
Results: Protein intake had no effect on Q (68.7 ± 7.3 μmol·kg−1·h−1; mean ± SE). F13CO2 displayed a robust biphase response (R2 = 0.66) with an estimated average requirement of 1.41 g·kg−1·d−1 and recommended dietary allowance of 1.71 g·kg−1·d−1.
Conclusions: The protein requirement estimate of 1.41 and 1.71 g·kg−1·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·kg−1·d−1) and at the upper range of the American College of Sports Medicine athlete recommendations (1.2–2.0 g·kg−1·d−1).
1Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON, CANADA; 2Frontier Research Laboratories, Institute for Innovation, Ajinomoto Co., Inc., Kawasaki, Kanagawa, JAPAN; 3Research Institute, Hospital for Sick Children, Toronto, ON, CANADA; 4Department of Nutritional Sciences, University of Toronto, Toronto, ON, CANADA; and 5Department of Pediatrics, University of Toronto, Toronto, ON, CANADA
Address for correspondence: Daniel R Moore, Ph.D., 100 Devonshire Place, Toronto, ON M5S 2C9, Canada; E-mail: firstname.lastname@example.org.
Submitted for publication March 2017.
Accepted for publication June 2017.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.acsm-msse.org).