Effect of High-protein Feeding on Performance and Nitrogen Balance in Female Cyclists

Purpose: The effect of dietary protein ingested after exercise on recovery in women athletes is unknown. Therefore, we asked whether there is a meaningful difference between high- and low-protein recovery diets on the subsequent performance of well-trained female cyclists.

Methods: In a crossover, 12 female cyclists completed three high-intensity rides composed of 2.5-h intervals on day 1, followed by repeat-sprint performance tests on days 2 and 4, interspersed with a rest day. During the 4-h recovery on days 1 and 2, cyclists ingested 1.4/0.7/0.26 or 2.1/0.1/0.26 g·kg(-1)·h(-1) of CHO/protein/fat in high-protein or isocaloric control conditions, respectively. At other times, cyclists ingested an isoenergetic high-CHO diet.

Results: No effect of protein dose on the mean power during repeat sprint was evident on day 2 (high-protein vs control = -1.1%; 95% confidence limits = ±4.6%) or on day 4 (1.7%; ±4.6%); furthermore, fatigue effects (slope) were unclear (day 2 = 1.4%; ±4.9%, day 4 = 0.5%; ±4.9%). Perceptions of leg tiredness and soreness were increased, and leg strength was reduced in the high-protein condition relative to control. In the high-protein condition, plasma glucose concentrations were lower during recovery, and plasma lactate concentrations were lower during the sprints. Effects on circulating creatine kinase activity were trivial. Net nitrogen balance during the experiment was positive in the high-protein condition (mean ± SD = 177 ± 140 mg of N·kg(-1) fat-free mass) but negative in the control condition (-81 ± 73 mg of N·kg(-1) fat-free mass); the estimated protein requirement was 1.28 g·kg(-1)·d(-1) (±0.57 g·kg(-1)·d(-1)).

Conclusions: In contrast with the previous findings in males, we observed no clear influence of dietary protein quantity on the subsequent performance in females. The findings on nitrogen balance suggest that female cyclists training intensely have daily protein requirements approximately 1.6 times the recommended daily allowance but 0.65 times that of males