Nitrogen metabolism of infants fed human and cow's milk

Abstract

Summary Nitrogen balance data on nine healthy infants indicate that nitrogen is slightly better retained from human than from cow's milk when both milks are fed at equiprotein and equicaloric levels. If correction is made for increased urea in human milk, the greater retention of nitrogen during feeding of human milk is of statistical significance. The increased nitrogen retention is apparently the result of better absorption of protein rather than of differences in metabolism of protein. Nitrogen balance studies of short duration may be misleading because of differences not associated with intake and output alone. Certain infants remained in positive nitrogen balance on feedings of 125 mg. nitrogen per kilogram per day, regardless of whether the source of the protein was human or cow's milk. This indicates that the protein of human and of cow's milk is approximately equal in biological value, and that infants may remain in positive nitrogen balance and grow satisfactorily on feedings of 0.8 Gm. protein per kilogram per day. One infant failed to thrive and could not be maintained in positive nitrogen balance except on human milk feeding. The superiority of human milk over cow's milk as an infant feeding is probably not related to superior biological value of the protein of human milk. The bacterial flora of the intestine, as determined by stool cultures, differs on feeding of human and of dilute cow's milk. A much greater proportion of the L. bifidus organisms present in the stools of babies fed human milk are of the variety “pennsylvanicus” than are those in the stools of infants fed cow's milk. A biological effect on the intestinal flora of the crude bifidus factor, as shown by a decrease in stool pH, is detectable in infants.