PLASMA FREE AMINO ACID CONCENTRATIONS OF BREAST‐FED INFANTS

Abstract
Photometric determination of .alpha.-amino N in peripheral venous plasma and urine from 20 healthy, full-term infants, 1-5 mo. of age, showing normal growth and development during an uncomplicated lactation, revealed lower plasma levels than found in adults, or 3.7 .+-. 1.1 mg/100 ml, and a urinary excretion of 41 .+-. 14 mg/24 h. Ion-exchange chromatography of deproteinized peripheral venous plasma showed low valine concentrations, an increased glycine/valine ratio and high cystine and very high taurine levels when compared to the levels of healthy. American infants of comparable ages fed 3-3.5 g/kg of cow-milk protein. The findings indicate that a formula based on cow-milk protein should optimally contain only 1.0-1.2 g protein/100 ml provided that it is humanized not only with regard to the lactalbumin/casein ratio, but also to the cystine and taurine content. The pattern of the plasma concentrations of free amino acids reported in the present investigation may be used as a normal reference for breast-fed infants.