No abstract

Growth, nutrient retention, and metabolic response of low-birth-weight infants fed human milk provided by their mother; this milk supplemented with bovine milk protein, calcium, phosphorus, and sodium; or pasteurized term human milk with the same supplement were monitored from the time desired intake was tolerated until weight reached 2200 g. The supplement resulted in greater rates of weight gain (20.5 +/- 2.3 vs 16.4 +/- 2.2 g.kg-1.d-1) and nitrogen retention (353 +/- 76 vs 270 +/- 53 mg.kg-1.d-1), increase in plasma transthyretin (TTR) concentration (7 +/- 16 vs -3 +/- 9 mg.L-1.wk-1), a higher mean plasma albumin concentration (34 +/- 3 vs 32 +/- 4 g/L), and a higher plasma TTR concentration at discharge (100 +/- 22 vs 75 +/- 24 mg/L). All these variables correlated significantly with total nitrogen intake, suggesting that the differences are attributable to the protein content of the supplement. The supplement also resulted in greater rates of calcium and phosphorus accretion but the plasma alkaline phosphatase activity of the supplemented vs the unsupplemented groups did not differ.

Carbohydrate and fat may vary in their ability to support protein accretion and growth. If so, variations in the source of nonprotein energy might be used to therapeutic advantage in enterally fed low-birth-weight infants. To test the hypothesis that high-carbohydrate diets are more effective than isocaloric highfat diets in promoting growth and protein accretion, low-birthweight infants weighing 750 -1600 g at birth were randomized in a double blind study to receive one of five formulas differing only in the quantity and quality of nonprotein energy. Groups 1, 2, and control received 130 kcal·kg -1 ·d -1 with 35, 65, and 50% of the nonprotein energy as carbohydrate. Groups 3 and 4 received energy intake of 155 kcal·kg -1 ·d -1 with 35 and 65% of the nonprotein energy as carbohydrate. Protein intake of all groups was 4 g·kg -1 ·d -1 . Growth and metabolic responses were followed weekly, and macronutrient balances including 6-h indirect calorimetry were performed biweekly. Greater rates of weight gain and nitrogen retention were observed at high-carbohydrate intake compared with high-fat intake at both gross energy intakes. Greater rates of energy storage and an increase in skinfold thickness were observed in group 4 (high-energy highcarbohydrate diet) despite higher rates of energy expenditure. These data support the hypothesis that at isocaloric intakes, carbohydrate is more effective than fat in enhancing growth and protein accretion in enterally fed low-birth-weight infants. However, a diet with high-energy and high-carbohydrate content also results in increased fat deposition. The American Academy of Pediatrics has suggested that a logical goal for nutritional support of the preterm LBW infant is to achieve postnatal growth approximating that of a normal fetus of the same postconceptional age (1, 2). Attempts to achieve this goal by feeding enriched diets have been successful in supporting the intrauterine rate of weight gain (3-7), but invariably these diets lead to a disproportionate increase in body fat. The reasons for this postnatal failure to maintain the high fetal rates of protein accretion relative to fat deposition are unknown. One difference between fetal and neonatal life is the relatively greater dependence of the fetus on carbohydrate versus fat as an energy source. If the fetus is relatively more dependent on carbohydrate than fat, then it is possible that the same is true of the fetus ex utero, i.e. the preterm LBW infant. This reintroduces a question of long-standing concern in developmental nutrition, namely, do carbohydrate and fat differ in some fundamental way in their ability to support protein synthesis? Indeed, there is experimental evidence that supports the hypothesis that calorie for calorie, utilization of carbohydrate as an energy source is more effective than fat in supporting protein accretion (8 -11); other research, however, asserts that this effect is transient (12). In enterally fed LBW infants, this hypothesis remains untested.LBW infants are ideal subjects for studying th...