Formula with reduced protein content: effects on growth and protein metabolism during weaning.

A total of 20 healthy term infants between 4 and 6 months of age were randomly assigned to either a low protein formula (F1.3) containing 1.3 g protein/100 ml or a high protein formula (F1.8) containing 1.8 g protein/100 ml. Both formulas were isocaloric (72 kcal/100 ml) and had a whey-casein ratio of 50:50. Ten control infants were breast-fed (BF). The mean protein intakes (including supplementary foods) were 1.9 +/- 0.3, 2.6 +/- 0.2, and 1.3 +/- 0.2 g/kg/day, respectively. The mean concentrations of serum urea were 2.8 +/- 0.6 (F1.3), 4.1 +/- 0.6 (F1.8), and 2.2 +/- 0.8 mmol/liter (BF) at 6 months (F1.3 versus BF, NS, F1.8 versus BF, p less than 0.001). The urine excretion of nitrogen was similar in the F1.3 and BF groups being 81 and 78 mg/kg/day. In the F1.8-group nitrogen excretion was higher, 138 mg/kg/day. Plasma concentrations of albumin, prealbumin, and transferrin were normal and similar in the groups. Weight gain was significantly higher in the F1.8 group, 22.8 +/- 1.7 g/kg/wk when compared to the F1.3 and BF groups, 19.9 +/- 3.9 and 18.0 +/- 4.3 (p less than 0.01), respectively. These data indicate that a decreased protein-intake from formula during weaning results in many indices of protein metabolism and growth more similar to those found in BF infants than when conventional follow-up formulas are used.