Protein quality of human milk fortifier in low birth weight infants: effects on growth and plasma amino acid profiles.

Serum preprandial essential amino acid, urea and prealbumin concentrations, and growth rates were studied in appropriate for gestational age low birth weight infants fed one of three regimens: (1) human milk enriched with human milk protein (n = 17); (2) bovine whey protein hydrolysate (n = 18; and (3) a mixture of bovine proteins, peptides and amino acids designed to have an amino acid composition close to that of human milk proteins (n = 18). Energy and nitrogen intakes were similar in all groups. Growth rates and gross metabolic responses did not differ between the feeding groups. There were also no differences in the amino acid profiles between those infants fed human milk protein fortifier and mixed bovine protein fortifier. Infants fed the whey fortifier had significantly higher threonine concentrations in comparison to those fed exclusively human milk protein (287 +/- 63 mumol/l vs 168 +/- 26 mumol/l) whereas the levels of some other essential amino acids (i.e. valine, leucine, lysine, histidine, phenylalanine and tryptophan) were lower. The results indicate that growth rates and gross metabolic indices do not depend on the protein quality of human milk fortifiers. However, the addition of well balanced mixtures of bovine proteins to human milk results in amino acid profiles similar to those observed in LBW infants fed similar amounts of human milk proteins.