Protein requirements of normal infants at the age of about 1 year: maintenance nitrogen requirements and obligatory nitrogen losses.

With 34 normal, healthy male infants aged 9-17 months, a total of 61 nitrogen (N) balance studies was conducted with N intake between 12 and 180 mg/kg/day. By regression analysis, the crude N maintenance requirements, either with whole egg or cow's milk protein, were estimated to be about the same, 106 and 103 mg/kg/day, respectively. The 97.5% confidence limits for the requirements were 128 (egg) and 142 (milk) mg/kg, respectively. Sums of the obligatory urinary and fecal N for the egg and milk protein series were 75 and 71 mg/kg as compared with 76 mg/kg of actually measured figure. Ratio of the maintenance N requirement to the obligatory N loss was 1.4. In another 15 N balance study, for which N intake from milk formulae ranged between 220 and 320 mg/kg/day, the mean apparent N retention was 25% of the intake. Total integumental N losses (skin + hair + nail) of infants fed 217-522 mg N/kg/day amounted to 7.8 +/- 2.9 mg/kg daily. Egg protein had somewhat higher digestibility than cow's milk protein, 92 versus 87%, but has lower biological value, 76 versus 82. Net protein utilization (NPU) estimated from the regression line was about the same for both proteins, 71 and 69, respectively.