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

Background: Although medium-chain triacylglycerols (MCTs) may be utilized m ore efficiently than long-chain triacylglycerols (LCTs), their effect on pr otein 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 ((x) over bar +/- 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, infant s received intravenous feeding providing 3 g lipid, 15 g glucose, and 3 g a mino acids.kg(-1).d(-1) and underwent 1) indirect calorimetry and 2) a prim ed, 2-h infusion of (HCO3Na)-C-13 to assess the recovery of C-13 in breath, immediately followed by 3) a 3-h infusion of L-[1-C-13]leucine. Results: The respiratory quotient tended to be slightly but not significant ly higher in the mixed MCT than in the LCT group (0.96 +/- 0.06 compared wi th 0.93 +/- 0.03). We did not detect a significantly difference between the mixed MCT and LCT groups with regard to release of leucine from protein br eakdown (B; 309 +/- 40 compared with 257 +/- 46 mu mol.k(-1).h(-1)) and non oxidative leucine disposal (NOLD; 296 +/- 36 compared with 285 +/- 49 mu mo l.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 mu mol.kg(-1).h( -1); P = 0.007). Net leucine balance (NOLD - B) was less positive in the mi xed MCT than in the LCT group (-14 +/- 9 compared with 28 +/- 10 mu mol.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.