Effects of formula protein level and ratio on infant growth, plasma amino acids and serum trace elements. II. Follow-up formula

Infants, that had been formula-fed from birth, were fed follow-up formula with 1.5, 2.2 or 2.9 g protein/dl together with 25 g of cereal/day as supplemental food, or formula only (15 g/dl). Formulas were started at 4 months of age and daily intake, anthropometric measurements and plasma samples taken at 5, 6 and 7 months. Protein intake was 2.0, 3.0 and 3.7 g/kg/d, respectively. Growth data were similar for all groups, as were hemoglobin and serum protein values. BUN values for the group fed only formula with 1.5 g protein/dl were lower than for the group fed the same formula with cereals and the other groups. Plasma amino acids were not affected by the addition of the small amount of cereals to the formula with 1.5 g protein/dl, but significantly higher levels of valine, leucine and histidine were found at 7 months for infants fed the two higher protein levels. The highest protein level also appeared to have a negative effect on plasma zinc levels. These results suggest that a protein level of 1.5 g/dl in follow-up formula (2.0 g/kg/d) is adequate during 4 to 7 months of age and that higher protein levels may be excessive.