C]linoleic acid metabolism in preterm infants fed a formula with medium-chain triglycerides

Most preterm infant formulas contain mediumchain triacylglycerols (MCT), but the effects of MCT on polyunsaturated fatty acid status and metabolism are controversial. Thus, we studied the effects of MCT on linoleic acid metabolism using stable isotopes. Enterally fed preterm infants were randomized to receive for 7 days 40% of fat as MCT (n 10) or a formula without MCT (n 9). At study day 5, infants received orally 2 mg/kg body weight of 13 C-labeled linoleic acid. Fatty acids in plasma lipid classes and 13 C enrichment of phospholipid fatty acids were measured and tracer oxidation was monitored. Compared with the control group, the MCT group showed lower breath 13 CO 2 and higher plasma triacylglycerol contents of octanoic acid, of decanoic acid, and of total long-chain polyunsaturated fatty acids (57.1 4.4 mol/l vs. 37.9 4.8 mol/l, P 0.01). Concentrations of several polyunsaturated fatty acids in plasma phospholipids and non esterified fatty acids were higher in the MCT group. 13 C concentrations in phospholipid n-6 fatty acids indicated no difference in the relative conversion of linoleic to arachidonic acid. We conclude that oral MCT effectively reduce polyunsaturated fatty acid and long chain polyunsaturated fatty acid oxidation in preterm infants without compromising endogenous n-6 long chain polyunsaturated fatty acid synthesis. — Rodriguez, M., S. Kiss, M. Fink, H. Demmelmair, M. Turini, G. Crozier, and B. Koletzko. Plasma fatty acids and [ 13 C]linoleic acid metabolism in preterm infants fed a formula with medium-chain triglycerides. J. Lipid Res. 2003. 44: 41–48. Supplementary key words long chain polyunsaturated fatty acid • tracer • long-chain triacylglycerols • LCT • fatty acid oxidation Preterm infant formulas are considered the best substitute for those premature infants who cannot receive sufficient amounts of human milk. The fat blend of preterm formulas contains up to 50% medium-chain fatty acids (8:0, 10:0; MCT) usually contributed by coconut oil (1). They are added to enhance fat and calcium absorption and to provide the premature infant with a readily available source of energy (2, 3). In addition, oral lipid supplementation containing a high percentage of MCT was shown to prevent the occurrence of hypoglycemia in low birth weight infants (4). In comparison to long-chain triacylglycerols (LCT), MCT are more efficiently absorbed in the digestive tract, and the liberated medium chain fatty acids (MCFA) are extensively and rapidly oxidized, whereas long chain fatty acids (LCFA) are largely stored in tissues (5). The intense lipid oxidation is associated with a ketogenic effect of dietary MCT, which provides an alternative energy source and is considered harmless for the infant as long as ketone body concentrations do not exceed values observed in breast fed infants (5, 6). Recent studies using stable isotopes have demonstrated that preterm infants are able to synthesize long-chain polyunsaturated fatty acids (LCP) such as arachidonic (20:4n-6) and docosahexaenoic acids (22:6n-3) from their precursor fatty acids, linoleic (18:2n-6) and -linolenic acids (18:3n-3) (7). Ingestion of MCT is associated with profound changes in plasma fatty acid composition (8, 9), but the effects of MCT on essential fatty acid and LCP status are controversial. Wall et al. (10) found significantly lower tissue levels of arachidonic acid in new-born piglets fed infant formulas containing MCT than in piglets fed formulas containing coconut oil (12:0 14:0). In premature infants, an interference of MCT on LCP metabolism was suggested by Carnielli et al. (9), who reported no effect on 20:4n-6 concentrations but a decrease in plasma phospholipid 22:6n-3 concentrations after MCT feeding. Abbreviations: AP, atom percent; APE, atom percent excess; LCFA, long chain fatty acid; LCP, long chain polyunsaturated fatty acids; LCT, long chain triacylglycerol; MCFA, medium chain fatty acids (8:0–12:0); MCT, medium chain triacylglycerols (8:0–12:0); MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; SFA, saturated fatty acids. 1 To whom correspondence should be addressed. e-mail: [email protected] Manuscript received 4 June 2002 and in revised form 19 August 2002. Published, JLR Papers in Press, September 1, 2002. DOI 10.1194/jlr.M200218-JLR200 by gest, on N ovem er 7, 2017 w w w .j.org D ow nladed fom