Amino acid concentrations in plasma and urine in very low birth weight infants fed protein-unenriched or human milk protein-enriched human milk

Preprandial plasma and urine amino acid concentrations were measured in 28 growing, very low birth weight, appropriate-for-gestational-age infants randomly assigned to either protein-unenriched (n = 14) or human milk protein-enriched (n = 14) human milk. The two groups of infants had similar birth weights (900 to 1500 g) and gestational ages (26 to 32 weeks). The study was initiated at a mean age of 19 days when the infants tolerated full feeding volumes and lasted for a mean time of 28 days. Mean protein intake values were 2.1 +/- 0.3 and 3.6 +/- 0.3 g/kg per day (mean +/- SD) and weight gain values were 26.6 +/- 7.4 and 35.1 +/- 3.6 g/day in the protein-unenriched and the protein-enriched groups of infants, respectively. Human milk protein enrichment resulted in significantly increased concentrations of all plasma amino acids except serine, taurine, and histidine. Most urine amino acid concentrations correlated with protein intake and with the plasma concentrations, suggesting that the effects of protein quality and quantity can be evaluated by measuring urinary amino acid concentrations alone, thereby making such studies less invasive. Infants fed protein-unenriched human milk had growth rates below the estimated intrauterine rate as well as low plasma and urine amino acid concentrations, indicating suboptimal protein intake levels. When the plasma concentrations of the essential amino acids in the protein-enriched infants from the present study were compared with concentrations found in the literature in fetal and umbilical cord plasma, both were found to be much higher.(ABSTRACT TRUNCATED AT 250 WORDS)