Plasma amino acids in term neonates after a feed of human milk or formula. II. Characteristic changes in individual amino acids.

Postprandial changes in plasma amino acids were studied in 23 term neonates who had previously been breast-fed ad libitum. As a test meal the infants received from a bottle a weight-based amount of banked human milk (true protein 0.8 g/100 ml) or formula with either 1.5 or 3.0 g of protein (adapted or non-adapted) per 100 ml. As regards the essential amino acids, all rose markedly in the plasma after the feed. The postprandial increments were relatively highest for the branched-chain amino acids, which rose 50-300% above the prefeeding concentrations. Peak values were found after human milk at 30 min but after formulas at 60 min. In extent and duration the rises were directly proportional to the amino acid loads given. This was also true for most semi- and non-essential amino acids, but plasma glycine, in contrast, regularly decreased, and plasma alanine continued to rise until 120 min after the beginning of the feed; neither change correlated with intake. After the milk feeds commonly given to neonates, postprandial alterations in plasma amino acids seem to be highly predictable.