This study examined if leucine, arginine or glycine supplementation in adult obese patients (body mass index of 33 ± 4 kg/m 2 ) consuming a Brazilian low energy and protein diet (4.2 MJ/day and 0.6 g protein/ kg) affects protein and amino acid metabolism. After four weeks adaptation to this diet, each subject received supplements of these amino acids (equivalent to 0.2 g protein kg -1 day -1 ) in random order. On the seventh day of each amino acid supplementation, a single-dose 15 N-glycine

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... y was carried out. There were no significant differences in protein flux, synthesis or breakdown. The protein flux (grams of nitrogen, gN/9 h) was 55 ± 24 during the nonsupplemented diet intake and 39 ± 10, 44 ± 22 and 58 ± 35 during the leucine-, glycineand arginine-supplemented diet intake, respectively; protein synthesis (gN/9 h) was 57 ± 24, 36 ± 10, 41 ± 22 and 56 ± 36, respectively; protein breakdown (gN/9 h) was 51 ± 24, 34 ± 10, 32 ± 28 and 53 ± 35, respectively; kinetic balance (gN/9 h) was 3.2 ± 1.8, 4.1 ± 1.7, 3.4 ± 2.9 and 3.9 ± 1.6. There was no difference in amino acid profiles due to leucine, arginine or glycine supplementation. The present results suggest that 0.6 g/kg of dietary protein is enough to maintain protein turnover in obese women consuming a reduced energy diet and that leucine, arginine or glycine supplementation does not change kinetic balance or protein synthesis. Correspondence