Increased Protein Requirements in Female Athletes after Variable-Intensity Exercise

Area of Science:

• Sports Nutrition
• Exercise Physiology
• Human Metabolism

Background:

• Protein requirements are often studied in isolation for resistance or endurance exercise.
• Variable-intensity intermittent exercise, common in team sports, has received limited research attention.
• Female athletes are underrepresented in sports nutrition studies, necessitating specific research.

Purpose of the Study:

• To determine the dietary protein requirement for active females engaged in variable-intensity intermittent exercise.
• To utilize the indicator amino acid oxidation (IAAO) method to assess protein needs.
• To test the hypothesis that protein requirements are higher than current estimates for nonactive adult males.

Main Methods:

• Six active females underwent metabolic trials during the luteal phase of their menstrual cycle.
• Participants performed a modified Loughborough Intermittent Shuttle Test followed by hourly protein-containing meals.
• The IAAO method with [C]phenylalanine was used to measure phenylalanine turnover, with CO2 excretion analyzed to determine protein requirements.

Main Results:

• Protein intake did not affect phenylalanine turnover (Q).
• Carbon dioxide excretion (FCO2) showed a significant biphase response.
• The estimated average requirement was 1.41 g·kg·d, and the recommended dietary allowance was 1.71 g·kg·d.

Conclusions:

• The determined protein requirement for active females is 1.41–1.71 g·kg·d.
• These requirements exceed IAAO-derived estimates for adult males (0.93–1.2 g·kg·d).
• The findings align with the upper range of recommendations for athletes by the American College of Sports Medicine.