Protein intake in early infancy: effects on plasma amino acid concentrations, insulin metabolism, and growth

The effects of different protein intakes on wt gain, insulin secretion, and plasma concentrations of amino acids have been evaluated in a prospective study involving 30 normal term infants. The infants were studied from 4.0 to 6.0 mo of age. Ten infants were breast-fed (BF), the others were randomly divided into two groups of 10 infants. One group was fed a formula containing 1.3 g protein/100 mL (F 1.3), the other a formula with 1.8 g protein/100 mL (F 1.8). The formulas were isocaloric (72 kcal/100 mL), and the fat concentrations were 3.5 g/100 mL (F 1.3) and 3.2 g/100 mL (F 1.8). All infants received the same supplementary foods. The urinary C-peptide excretion in the infants fed the F 1.8-formula was 4.4 +/- 2.1 nmol/mmol creatinine or 19.4 +/- 12.9 nmol/m2, significantly higher than that in the infants fed the F 1.3-formula (2.6 +/- 1.5 and 7.9 +/- 5.1) or the BF infants (1.7 +/- 1.4 and 6.3 +/- 6.0). Gain in wt was 18.0 +/- 4.3, 19.9 +/- 3.9, 22.8 +/- 1.6 g/kg/wk and corresponded to protein intakes of 1.3 +/- 0.2, 1.9 +/- 0.3, and 2.6 +/- 0.2 g/kg/d, in the BF, F 1.3, and F 1.8 groups, respectively. Gain in length was 6.7 +/- 1.8 (BF-group), 6.2 +/- 2.5 (F 1.3-group), and 7.6 +/- 2.2 (F 1.8-group) mm/m/wk. Wt gain correlated with urinary C-peptide excretion at 6.0 mo (r = 0.51, p less than 0.01) and with protein intake (r = 0.43, p less than 0.01).