Effects of type of dietary protein on acid-base status, protein nutritional status, plasma levels of amino acids, and nutrient balance in the very low birth weight infant.

STUDY OBJECTIVE: To determine the effect of the type of dietary protein (3.3 gm/kg per day) on acid-base status, protein nutritional status, plasma amino acid concentrations, and nutrient (nitrogen, fat, mineral, trace element) balance. SUBJECTS: Preterm infants (birth weight less than or equal to 1250 gm, gestational age less than or equal to 32 weeks) with no evidence of systemic disease, who had achieved a minimal enteral intake of 110 kcal/kg per day by 21 days of age. INTERVENTIONS: Each infant was fed three study formulas that differed only with respect to the ratio of whey to casein (60:40, 35:65, 18:82). Each formula was given for 1 week. At the end each week, blood was drawn and a 48-hour balance was determined. MAIN RESULTS: Late metabolic acidosis, uremia, and hyperammonemia were not observed. No differences in pH or serum bicarbonate were noted. Base excess was greater with the casein-predominant formula (18:82 greater than 35:65, 60:40) but remained within normal limits for the preterm infant. Plasma concentrations of threonine (60:40 greater than 35:65 greater than 18:82), phenylalanine, and tyrosine (18:82 greater than 35:65 greater than 60:40) differed. Nitrogen absorption (60:40 less than 35:65, 18:82), nitrogen retention (60:40 less than 35:65, 18:82), fat absorption (60:40, 35:65 greater than 18:82), and phosphorus absorption (60:40 less than 35:65, 18:82) also differed. CONCLUSIONS: At an intake of 3.3 gm/kg per day, the type of dietary protein had little effect on metabolic status. Differences in plasma amino acid concentrations and nutrient balance suggest that a formula containing protein with a whey/casein ratio of 35:65 may be preferable to that with a whey/casein ratio of 60:40 or 18:82 for the very low birth weight infant.

Vitamin D and mineral metabolism in the very low birth weight infant receiving 400 IU of vitamin D.

STUDY OBJECTIVE: To examine (1) the effect of vitamin D intake (380 to 480 IU daily) on plasma 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D (1,25-(OH)2D) concentrations and (2) the relationship of 1,25-(OH)2D to calcium and phosphorus absorption and retention in the very low birth weight infant receiving a preterm infant formula. SUBJECTS: Eleven "well" infants with a birth weight and gestational age (mean +/- SD) of 1078 +/- 128 gm and 29 +/- 1.9 weeks, respectively, were studied for a 3-week period. Weight and postnatal age (mean +/- SD) at the beginning of the study were 1132 +/- 56 gm and 16 +/- 6 days, respectively. All infants were fed a preterm infant formula and tolerated a full enteral intake (120 kcal/kg/day) for the duration of the study. INTERVENTIONS: Plasma 25-OHD and 1,25-(OH)2D concentrations were measured at the beginning of the study and at the beginning of each 48-hour balance period. Calcium and phosphorus balance studies (n = 33) were performed weekly. MAIN RESULTS: Plasma 25-OHD (30 +/- 10 ng/ml) and 1,25-(OH)2D (54 +/- 14 pg/ml) concentrations were normal at the beginning of the study. Plasma 25-OHD values did not change, but 1,25-(OH)2D values increased (p less than 0.001) throughout the study. Plasma 1,25-(OH)2D concentrations were not related to calcium or phosphorus absorption and retention, but were a linear function of postconceptional age. CONCLUSIONS: Normal vitamin D status and activity are maintained in the very low birth weight infant fed a high calcium formula (380 to 480 IU of vitamin D daily). Plasma 1,25-(OH)2D concentrations are not related to calcium absorption but are linearly related to maturity.