Shute, M., Rankin, J. W., Saker, K., & Heffron, S. (2004). Effect of whey protein isolate on oxidative stress, exercise performance, and immunity. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 1183.

This study evaluated the effect of a whey protein isolate, a reported glutathione booster, on exercise performance, immune function, and antioxidant status during weight maintenance and energy restriction in college-age male cyclists (N = 20). Ss performed a submaximal cycling exercise test for 45 minutes immediately followed by a performance test set at 90% VO2peak until exhaustion. Blood samples were collected before, after 45 minutes, at exhaustion, and one hour after exercise and analyzed for tGSH, GSH/GSSG ratio, white blood cell glutathione, glutathione peroxidase, lipid hydroperoxides, and several immunity measures. Ss consumed 40 g/day of whey protein isolate or casein placebo (P) along with their normal diet for two weeks, repeated the exercise test, and then began a low energy diet (20 kcal/kg/d), continuing the same supplementation, for four days before the final exercise test.

Whey protein isolate was not associated with superior exercise performance, antioxidant status, or immune function following exercise or weight loss.

Implication. Supplementation with whey protein isolate did not enhance glutathione status, exercise performance, or exercise-induced immune changes, in trained cyclists, during weight maintenance or energy restriction. Energy restriction reduced indicators of oxidative stress.

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