Comparison of two preterm formulas with or without addition of medium-chain triglycerides (MCTs). I: Effects on nitrogen and fat balance and body composition changes

Medium-chain triglycerides (MCTs) are included in the fat blend of several preterm formulas because of their complete absorption and rapid oxidation. The effects of two different fat blend compositions on nitrogen and fat balances and macronutrient oxidation were investigated in 28 healthy very-low-birth weight infants at 4 weeks of age. A preterm formula with a traditional corn oil/MCT blend containing 38% MCTs (MCT group) was compared to a new fat blend, designed to resemble human milk more, containing 6% MCTs (LCT group). There were no differences in nitrogen absorption or in excretion. Median nitrogen retention was 74% (MCT) vs. 71% (LCT) of intake. Fat absorption was higher (p < 0.05) in the MCT group (88%) vs. 79% in the LCT group (median values). MCTs did not stimulate fatoxidation as measured by indirect calorimetry, so fat deposition was also higher on the MCT formula. As weight gain was not different between groups, the percentage of weight gain consisting of fat accretion was significantly (p< 0.005) higher with the MCT formula (24% vs. 21%). On the other hand, there was no increase in percent protein accretion (both 15% of weight gain). We conclude that the existence of a slightly lower fat absorption in the healthy growing neonate fed a LCT formula compared with a MCT formula does not impair growth or nitrogen retention, but merely induces a slight decrease in the high relative fat accretion encountered in the preterm neonate.