Effect of diet on plasma aminograms of low birth weight infants.

The composition of nutrient mixtures for the low birth weight infant is a matter of considerable concern, and questions have been raised about the adequacy of the cystine and tyrosine contents of available preparations. Low birth weight infants were fed isonitrogenous isocaloric formulas whose content of tyrosine and cystine varied 3- and 7-fold, respectively, for 3-day periods in a Latin Square design. Two-hour postprandial plasma aminograms indicate a statistically significant difference (P = 0.05) between plasma cystine levels noted in infants fed the formula containing cystine at 6 mg/100 ml and those fed the formula containing cystine at 28 mg/100 ml. No significant differences were noted between other formula groupings. Plasma tyrosine concentrations were rapidly reduced whenever tyrosine intake was less then 50 mg/kg of body weight. Such a dietary approach may be of value in reduction of the elevated plasma tyrosine levels seen in infants with transient tyrosinemia of prematurity. Postprandial concentrations of plasma amino acids for the low birth weight infant are a useful reference standard for evaluation of the response of the low birth weight infant to new therapeutic feeding mixtures, particularly parental or jejunal feedings.