Metabolic and energy balance in small- and appropriate-for-gestational-age, very low-birth-weight infants.

This study compared nutrient utilization and postnatal weight gain composition in eight appropriate for gestational age (AGA: birth weight 1293 +/- 107 g; gestational age 28.8 +/- 1.4 weeks) and eight symmetrically growth-retarded (SGA: birth weight 1110 +/- 230 g; gestational age 32.7 +/- 1.9 weeks), very low-birth-weight (VLBW) infants. There was no significant difference in protein, mineral and energy intake between AGA and SGA infants. Nitrogen absorption (84 +/- 3 and 83 +/- 4%) and nitrogen retention (356 +/- 48 and 352 +/- 43 mg/kg/day) were similar in both groups. Fat absorption tended to be lower in AGA (78 +/- 15%) than in SGA (87 +/- 4%) infants. Calcium, phosphorus and magnesium absorptions were similar in AGA and SGA infants. Metabolizable energy utilization was similar in both groups; about 55% was expended and 45% stored in new tissues. Energy expenditure was 58 +/- 4 kcal/kg/day in SGA infants and 61 +/- 9 kcal/kg/day in AGA infants. Weight gain and its composition were similar in both groups. We conclude that nutrient and energy utilization are similar in AGA and symmetrically growth-retarded, VLBW infants.