Leucine metabolism in preterm infants receiving parenteral nutrition with medium-chain compared with long-chain triacylglycerol emulsions

Abstract

Background: Although medium-chain triacylglycerols (MCTs) may be utilized more efficiently than long-chain triacylglycerols (LCTs), their effect on protein metabolism remains controversial. Objective: The aim of the study was to compare the effects of mixed MCT-LCT and pure LCT emulsions on leucine metabolism in preterm infants. Design: Fourteen preterm [gestational age: 30 ± 1 wk; birth weight: 1409 ± 78 g (x̄ ±SE)] neonates were randomly assigned to receive, from the first day of life, either a 50:50 MCT- LCT (mixed MCT group; n = 7) or an LCT (LCT group; n = 7) lipid emulsion as part of an isonitrogenous, isoenergetic total parenteral nutrition program. On the fourth day, infants received intravenous feeding providing 3 g lipid, 15 g glucose, and 3 g amino acids · kg-1 · d-1 and underwent 1) indirect calorimetry and 2) a primed, 2-h infusion of H13CO3Na to assess the recovery of 13C in breath, immediately followed by 3) a 3-h infusion of L-[1-13C]leucine. Results: The respiratory quotient tended to be slightly but not significantly higher in the mixed MCT than in the LCT group (0.96±0.06 compared with 0.93±0.03). We did not detect a significant difference between the mixed MCT and LCT groups with regard to release of leucine from protein breakdown (B; 309 ± 40 compared with 257 ± 46 μmol · kg-1 · h-1) and nonoxidative leucine disposal (NOLD; 296 ± 36 compared with 285± 49 μmol · kg-1 · h-1). In contrast, leucine oxidation was greater in the mixed MCT than in the LCT group (113 ± 10 compared with 67 ± 10 μmol · kg-1 · h-1; P = 0.007). Net leucine balance (NOLD - B) was less positive in the mixed MCT than in the LCT group (-14 ± 9 compared with 28 ± 10 μmol · kg-1 · h-1; P = 0.011). Conclusion: Mixed MCTs may not be as effective as LCT-containing emulsions in promoting protein accretion in parenterally fed preterm neonates.