Plasma amino acids after a feed of human milk or formula at three months of age.

Prefeeding plasma amino acid concentrations were higher and glycine-to-valine ratios lower in formula-fed infants as compared to breast-fed infants at 3 months of age. After a human milk meal (true protein, 0.8 g/100 ml) or formula meal (1.5 g/100 ml), all essential and several nonessential amino acids peaked at 30-60 min. The postprandial increments were greater and lasted longer after formula, reflecting the amounts of individual amino acids in the feeds. The changes resembled those seen in adults, and were smaller than those observed in these infants at 1 week of age. These data indicate that gastrointestinal, hepatic, and endocrine responses to a meal are immature at the age of 3 months.