Feeding Preterm Infants After Hospital Discharge: Effect of Diet on Body Composition.

Feeding Preterm Infants After Hospital Discharge: Effect of Diet on Body Composition. Cooke RJ, McCormick K, Griffin IJ, et al. Pediatr Res 1999;46:461–4. Summary: Cooke et al. conducted a prospective, blinded, and randomized trial to compared body composition, using dual-energy x-ray absorptiometry (DEXA) during dietary intervention in 129 normally growing preterm infants (birth weight ≤1750 g and gestation ≤34 weeks). At hospital discharge, infants were randomized to be fed either a preterm infant formula from discharge to 6 months (group A, n = 49), a term formula from discharge to 6 months (group B, n = 54), or the preterm formula from discharge to term and then the term formula from term to 6 months (group C, n = 26). All infants were fed on demand. Compared with the term formula, the preterm formula had higher energy (80 vs. 66 kcal/100 mL), protein (2.2 vs. 1.4 g/100 mL), calcium (108 vs. 54 mg/100 mL), and phosphorus (54 vs. 27 mg/100 mL). The infants were seen biweekly (discharge to term) and then monthly (term to 6 months), when intake was measured and anthropometry and blood sampling were performed. Body composition was measured at regular intervals by DEXA (QDR 2000; Hologic Inc., Waltham, MA, U.S.A.) and special software (Infant Whole Body Software, ver. 5.56P; Hologic). Patient characteristics were similar between the treatment groups. The mean (±SD) energy intakes (group A 108 ± 36, Group B 106 ± 32, and Group C 105 ± 32 kcal/kg per day) were similar, but protein and mineral intakes differed between the groups (A > C > B;P < 0.0001). During follow-up, differences were noted between group A (fed preterm formula throughout the study) and group B (fed the term formula throughout the study). The boys in group A had higher mean weight, lean body mass, fat mass, and bone mineral mass than those in group B. Body composition by DEXA showed that the weight gain was mainly due to increase in lean body mass, which was postulated to be due to differences in protein intake and/or the ratio of protein to energy. The effects of the diet were confined to boys, with no lasting effect in girls. This is the first study to demonstrate differences in growth rates between preterm boys and girls with similar nutrient intake. The authors concluded that preterm formula is more suitable for the needs of rapidly growing preterm male infants after hospital discharge. Comment: Advances in neonatology have increased the survival of premature infants (BMJ 1997;314:107–11;Am J Obstet Gynecol 1995;172:457–64). The majority undergo intensive nutritional management during their hospital stays but are discharged home on food suitable for healthy term infants. Studies have shown that they grow slowly (J Pediatr 1990;117:298– 307;Acta Paediatr Scand 1987;76:636–46), and slow growth has been related to poor outcome (BMJ 1999;318:427–31;Clin Pediatr (Phila) 1993;32:405–11;Lancet 1989;11:577–80;J Pediatr 1985;107:284–86). Body composition is fundamental to understanding the growth process, it permits evaluation of the effects of nutritional intervention, and there is a need for a rapid, safe, and precise method. In the past, all studies have been hospital based using metabolic balances and indirect calorimetry. Only recently have noninvasive methods such as DEXA been used. Although there is no gold standard method to assess body composition in infants (J Pediatr Gastroenterol Nutr 1999;29:184–9), DEXA has been shown to be a relatively precise and noninvasive method (Pediatr Res 1997;41:590–6;Am J Cli Nutr 1996;63:157–63). However, its accuracy may be affected by infant size (J Pediatr Gastroenterol Nutr 1999;29:184–9;Am J Clin Nutr 1993;58:589–91). Cook et al. demonstrated in the present study that DEXA was precise enough to detect differences in body composition during dietary intervention. The current recommended intake for preterm infants are: energy, 105 to 130 kcal/kg per day; protein, 3.5 to 4 g/kg per day; iron, 2 to 4 mg/kg per day (maximum, 15 mg/day); vitamin D, 400 IU/day; and a multivitamin supplement until the infant reaches a weight of 2.5 kg (Can Med Assoc J 1995;152:1765–85;Pediatrics 1985;75:976–86;Acta Paediatr Scand Suppl 1987;336:1–14). An intake volume of 200 mL/kg per day of expressed breast milk or term formula (energy density, 65 kcal/100 mL) can achieve the recommended intake for energy but not for protein and minerals. Feeding with fortified human milk or enriched preterm formulae at 150 to 180 mL/kg per day can achieve the above recommendations and has been shown to be safe and beneficial (Pediatrics 1999;103:1150–7;Lancet 1990;335:1477–81;Arch Dis Child 1989;64:1570–8). Until now, it has not been clear whether continuing with a similar nutrient intake after hospital discharge improves growth during the first year of life. Few studies have been performed to evaluate the effect of diet on the growth of preterm infants in the post–hospital discharge period. A randomized double-blind trial comparing preterm formula, term formula, and exclusive breast-feeding demonstrated that preterm formula-fed infants had greater mean length and head circumference at 12 weeks after discharge (J Perinatol 1996;16:111–6). Another randomized double-blind trial comparing the growth of preterm infants (n = 32) fed a nutrient-enriched postdischarge formula (energy, 72 kcal/100 mL; protein, 1.85 g/100 mL; fat, 4.0 g/100 mL) versus a standard term formula, demonstrated significant increases in linear growth and weight gain at 9 months of age in those fed the enriched formula (Arch Dis Child 1992;67:324–7). When added to the mother's milk, commercially available milk fortifiers raise the nutrient concentrations to levels similar to the preterm formula milk. Improved growth has been demonstrated preterm infants in the hospital fed human milk with added fortifiers (Int J Clin Pract 1998;52:236–40), but there are very few studies using them in the postdischarge period. Wauben et al. performed the first prospective study to demonstrate the impact of dietary manipulation on body composition of preterm infants (Acta Paediatr 1998;87:780–5). They compared anthropometry and body composition in three groups of preterm infants (n = 37) fed with either mother's milk with a multinutrient fortifier, mother's milk with calcium and phosphorus supplements, or a preterm formula (Preemie SMA; Wyeth Ayerst, Ontario, Canada) to 1 year corrected age. The preterm formula group had higher bone mineral content (BMC) and lesser percentage fat mass at 12 months. They also had consistently higher weight than the other two groups. Short-term (mean, 4 weeks) feeding with a preterm milk formula significantly improved developmental status at 18 months after term in 424 infants studied by Lucas et al. (Lancet 1990;335:1477–81). Growth and nutrition in early life may affect long-term health and development in these infants (Arch Dis Child 1994;71:288–90). If the present trend of increasing survival of preterm infants continues, more infants will be discharged home at body weight of 1800–2000 g. These infants need nutritional management after hospital discharge to optimize their growth and development. Studies have shown the benefits of continuing with nutrient-enriched human milk or preterm infant formula feeding well into the first year of life. The optimal formula composition for preterm infants after hospital discharge remains to be determined.

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