Effects of feeding ultrahigh-temperature (UHT)-treated infant formula with different protein concentrations or powdered formula, as compared with breast-feeding, on plasma amino acids, hematology, and trace element status.

The appropriate amount of protein to use in infant formula is still under discussion. We found earlier that protein digestibility is higher from ultrahigh-temperature (UHT)-treated formula than from conventionally heat-treated formula. In this study, we evaluated the nutritional, hematologic, and biochemical effects of feeding infants whey-predominant UHT-treated formula with 13 (UHT-13) or 15 (UHT-15) g protein/L as compared with a conventional, powdered, whey-predominant formula (PF) with 13 g protein/L from 6 wk to 6 mo of age. Breast-fed infants served as control subjects. Growth was assessed at monthly intervals and venous blood samples were drawn at entry into the study and at 6 mo of age. At 6 mo, there were no significant differences in weight gain or linear growth, or hemoglobin, serum ferritin, zinc, or copper concentrations among the groups. Blood urea nitrogen concentrations were lowest for breast-fed infants; among the formula-fed groups the UHT-13 group had the lowest values. All formula-fed groups had higher plasma threonine concentrations than breast-fed infants. Infants fed the UHT-13 formula had threonine values closest to those of breast-fed infants. Concentrations of branched-chain amino acids were similar in breast-fed infants and those fed UHT-13 formula, whereas the other groups had higher values. Plasma tryptophan concentrations were significantly higher in the UHT-treated formula groups than in the other groups. Thus, infants fed UHT-13 formula had metabolic measures similar to those of breast-fed infants, possibly because of high protein digestibility, or a difference in the protein source used. Iron, zinc, and copper status was satisfactory in all groups. Selenium status, as indicated by serum glutathione peroxidase activity, varied with dietary selenium intake.