Quantity and quality of milk protein intake: metabolic responses in the neonate.

All whey proteins in human milk are not absorbed and thus not nutritionally available. There is evidence that SIgA, lactoferrin and lysozyme are resistant to proteolytic action and the major part of these protective proteins are excreted in the infants stool. An exclusively breast-fed infant would thus have a mean intake of 1.3 g of protein per kg/d during the first month and about 0.9 g/kg/d during the third month. Term infants fed with formulas containing 1.5 g of protein per 100 ml show metabolic changes which indicate that they receive more protein than they require for growth, these changes are not seen in breast-fed infants or in infants receiving a whey-predominant formula containing only 1.1 g/100 ml of protein. A reevaluation of protein requirement and intake during infancy is suggested.