Cereal feeding and its impact on the nitrogen economy of the infant.

To quantify the effect of rice cereal on nitrogen balance and fecal nitrogen excretion, and the contribution of endogenous nitrogen sources to fecal nitrogen output, nine infants aged 3-5 mo received [15N]glycine in all feedings. Samples of urine and feces were obtained daily and analyzed for nitrogen and 15N. On days 1-7 the infants received only formula, and a complete urine and fecal collection was made on days 6-7. From days 8 to 12 the formula was supplemented with rice cereal (133.3 g/L, or 4 g/30 mL formula) and a second complete urine and fecal collection was made on days 11-12. Cereal did not alter fecal nitrogen output or the calculated contribution (45%) of endogenous nitrogen to fecal nitrogen. Cereal did increase nitrogen retention and lower the urinary excretion of the 15N dose (24% of dose). The calculated true digestibility of the rice cereal protein was > 95%. Our results indicate that infants aged 4 mo, in contrast with younger infants, are able to digest and absorb cereal. The addition of cereal to the diet does not lead to increased fecal protein losses.