Effects of formula protein level and ratio on infant growth, plasma amino acids and serum trace elements. I. Cow's milk formula.

The optimum level and ratios of protein to be used in cow's milk formula has recently been under discussion. Healthy term infants were fed from birth exclusively human milk or a formula that varied in protein level or whey: casein ratio: (A) 1.4 g/dl; 55:45, (B) 1.5 g/dl; 55:45, (C) 1.3 g/dl; 55:45, (D) 1.4 g/dl; 60:40, (E) 1.4 g/dl; 20:80. Infants were followed for 12 weeks and blood samples were taken at 2, 4, 8 and 12 weeks. Anthropometric indices did not show any significant differences among groups. Plasma amino acid and BUN levels of the C group were closest to the breast-fed group, while the formula with the highest protein level (B) resulted in high values for some amino acids. When comparing the formulas with 1.4 g protein/dl, the high casein group had the lowest plasma tryptophan levels. Taurine was added to all formulas at a level similar to that of breast milk; plasma taurine levels were similar for all groups. All formulas contained 0.7 mg iron and 0.7 mg zinc/dl; no differences were found among the groups in hematological indices or serum trace elements. These data show that feeding a formula with 1.3 g protein/dl and 55:45 whey: casein ratio from birth will result in growth and metabolic indices similar to those of breast-fed infants, although some plasma amino acid levels are not identical, 1990.