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 15N-glycine study 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-, glycine- and 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.