Whole-body protein metabolism turnover in men on a high or low calorie rice and bean Brazilian diet

Whole-body protein kinetics was measured with N-15-glycine in five young adult male volunteers. Each subject participated twice, being his own control. They received a Brazilian rice and bean diet with usual Brazilian protein intake of 0.8 g/kg/d, but low (-30%) or high (+30%) in non-protein calories. The subjects were fed, at random, for 7-8 days the low or high calorie diet. During the last three days samples of food, feces and urine were collected for nitrogen balance. On the last day, rates of nitrogen flux, protein synthesis and degradation in the whole body were estimed from N-15 excretion in urinary ammonia and total urea (excreted plus retained within the body) during a 9-h period after administration of oral single dose of N-15-glycine. During the kinetic study the subjects received 1/12 of the total food intake hourly. The results were for the low and high calorie intakes respectively: nitrogen balance, mg/kg/d, 2+/-21 (mean+/-SD) and 24+/-16 (p<0.05); urine nitrogen, mg/kg/d, 104+/-9 and 89+/-18 (p<0.11); nitrogen flux, g/9h, 21+/-6 and 18+/-4; protein synthesis, g/9h, 112+/-44 and 94+/-24 protein breakdown, g/9h, 101+/-41 and 81+/-26. In conclusion, healthy young adult receiving low calorie rice and beans Brazilian diet maintained the nitrogen flux, protein synthesis and degradation constant, in spite of a lower nitrogen balance.