Obligatory N loss and utilization of egg and rice mixed protein in young japanese women.

Obligatory urinary and fecal N losses in young Japanese women were evaluated and the effect of energy intake on the utilization of rice and egg mixed protein was investigated in subjects receiving a low protein diet. Seven female students were given a protein-free diet for ten days. Feces and 24-h urine samples were collected throughout the period and their nitrogen contents were analyzed. Basal metabolism was measured and the lean body mass was calculated from urinary creatinine excretion by the equation of Forbes. The mean weight loss of the 7 subjects during the ten days was 1.5 kg, the mean obligatory urinary N loss was 32.3 +/- 5.9 mg/kg body weight, 1.67 +/- 0.45 mg/kcal basal metabolism, or 1.68 +/- 0.32 g/g creatinine, and the mean obligatory fecal N loss was 10.1 +/- 2.0 mg/kg body weight, or 0.51 +/- 0.08 mg/kcal basal metabolism. In a second experiment, 17 female subjects were divided into three groups with an energy intake of about 35, 42, 46 kcal/kg BW, respectively. During the 7-day experimental period, they were given a low protein diet containing 250 g of rice and 125 g of whole egg. The nitrogen contents of the 24-h urine samples and feces collected were analyzed and the nitrogen balance was calculated as the difference between N intake and urinary and fecal N excretion. Subjects with an energy intake of 35 kcal/kg BW had a negative N balance, while subjects with an intake of 46 kcal/kg BW achieved an apparent positive N balance. The NPU values of rice and egg mixed protein with energy intake of 35, 42, 46 kcal/kg BW were calculated from the N balance data and the values for obligatory urinary and fecal N losses in the first experiment as 25, 37 and 54, respectively.