Send to

Choose Destination
Med Sci Sports Exerc. 2017 Nov;49(11):2297-2304. doi: 10.1249/MSS.0000000000001366.

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

Author information

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.



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.


Six females (21.2 ± 0.8 yr, 68.8 ± 4.1 kg, 47.1 ± 1.2 mL O2·kg·min; 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·d), 6 g·kg·d CHO and sufficient energy for resting and exercise-induced energy expenditure. Protein was provided as crystalline amino acid modeling egg protein with [C]phenylalanine as the indicator amino acid. Phenylalanine turnover (Q) was determined from urinary [C]phenylalanine enrichment. Breath CO2 excretion (FCO2) 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.


Protein intake had no effect on Q (68.7 ± 7.3 μmol·kg·h; mean ± SE). FCO2 displayed a robust biphase response (R = 0.66) with an estimated average requirement of 1.41 g·kg·d and recommended dietary allowance of 1.71 g·kg·d.


The protein requirement estimate of 1.41 and 1.71 g·kg·d for females performing variable-intensity intermittent exercise is greater than the IAAO-derived estimates of adult males (0.93 and 1.2 g·kg·d) and at the upper range of the American College of Sports Medicine athlete recommendations (1.2-2.0 g·kg·d).

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Wolters Kluwer
Loading ...
Support Center