ABSTRACT

This chapter explores the complexities of amino acid metabolism in milk-fed infants, examines some of the plasma amino acid data reported to date, and reviews the implications of these data for research in the future. The composition of human milk initially was used to guide infant formula manufacturers in the formulation of human milk substitutes. Recent information will be reviewed in this chapter that points out certain discrepancies that result from this approach. The nitrogen metabolism of the human milk-fed infant is the appropriate model to which human milk substitutes can be compared. Plasma amino acid concentrations of milk-fed infants have proven to be reliable, sensitive indicators of nitrogen metabolism. The metabolic response to the feeding of infant formula should duplicate that of the breast-fed infant. As formulas have become more refined, in vivo biochemical studies of formula-fed infants are required to discriminate differences among currently available products. Also presented is a limited discussion of nitrogen metabolism in low-birth-weight infants, the importance of adequate mineral intake for optimal protein utilization, and suggestions for future research.