Cribb, P. J., Williams, A. D., Hayes, A., & Carey, M. F. (2002). The effect of whey isolate and resistance training on strength, body composition, and plasma glutamine. Medicine and Science in Sports and Exercise, 34(5), Supplement abstract 1688.

This study examined the effects of two common dietary protein supplements, whey isolate and caseine, on strength, body composition, and plasma glutamine levels during a 10-week intense resistance training program. Trained males were formed into a whey isolate group (N = 6) and a caseine group (N = 7). Supplementation was similar for both groups at 1.5 gm/kg/day.

Whey isolate produced a significantly greater increase in lean body mass and greater strength gains in each of the three test exercises than did the caseine group. The whey group also decreased fat mass significantly more than the caseine group. Plasma glutamine levels did not change in either group.

Implication. Whey protein was effective for increasing muscle mass, strength, and decreasing fat mass whereas caseine was ineffective. Both supplements prevented a decline in plasma glutamine level, which commonly occurs with intense resistance training.

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