Purpose: We determined the effects of conjugated linoleic acid (CLA) supplementation during resistance training. Methods: Seventy-six subjects were randomized to receive CLA (5 g[middle dot]d-1) or placebo (PLA) for 7 wk while resistance training 3 d[middle dot]wk-1. Seventeen subjects crossed over to the opposite group for an additional 7 wk. Measurements at baseline, 7 wk, and 14 wk (for subjects in the crossover study) included body composition, muscle thickness of the elbow flexors and knee extensors, resting metabolic rate (RMR), bench and leg press strength, knee extension torque, and urinary markers of myofibrillar degradation (3-methylhistidine (3MH) and bone resorption (cross-linked N-telopeptides (Ntx)). Results: After 7 wk the CLA group had greater increases in lean tissue mass (LTM) (+1.4 vs +0.2 kg; P < 0.05), greater losses of fat mass (-0.8 vs +0.4 kg; P < 0.05), and a smaller increase in 3MH (-0.1 vs + 1.3 [mu]mol[middle dot]kg-1 LTM[middle dot]d-1; P < 0.05) compared with PLA. Changes between groups were similar for all other measurements, except for a greater increase in bench press strength for males on CLA (P < 0.05). In the crossover study subjects had minimal changes in body composition, but smaller increases in 3MH (-1.2 vs +2.2 [mu]mol[middle dot]kg-1 LTM[middle dot]d-1; P < 0.01) and NTx (-4.8 vs +7.3 nmol[middle dot]kg-1 LTM[middle dot]d-1; P < 0.01) while on CLA versus PLA. Conclusions: Supplementation with CLA during resistance training results in relatively small changes in body composition accompanied by a lessening of the catabolic effect of training on muscle protein.
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