Increased Protein Requirements in Female Athletes after Variable-Intensity Exercise

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


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·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.

Results: 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.

Conclusions: 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).

MeSH terms

  • Accelerometry
  • Breath Tests
  • Dietary Proteins / administration & dosage
  • Dietary Proteins / metabolism*
  • Energy Metabolism
  • Exercise / physiology*
  • Female
  • Humans
  • Luteal Phase
  • Nutritional Requirements*
  • Oxidation-Reduction
  • Phenylalanine / urine
  • Pregnanediol / analogs & derivatives
  • Pregnanediol / urine
  • Sex Factors
  • Sports / physiology*
  • Young Adult


  • Dietary Proteins
  • pregnanediol-3 alpha-glucuronide
  • Phenylalanine
  • Pregnanediol