Effects of glucose-to-lipid ratio and type of lipid on substrate oxidation rate in patients

This study is an investigation into the effects of different carbohydrate-to-lipid ratios on CO2 production in postoperative patients and the determination of the substrate oxidation rates induced by long-chain triglycerides (LCT) or a mixture of long- and medium-chain triglycerides (MCT/LCT) at various carbohydrate-to-lipid ratios. Two groups of eight patients randomly received either LCT or MCT/LCT emulsions. Total caloric intake was set at the measured energy expenditure provided at three different glucose-to-lipid ratios (70:30, 50:50, 30:70). We used long-term indirect calorimetry with a mass spectrometer system and measurement of natural enrichment in 13C of expired CO2 and plasma glucose. The carbon dioxide production and minute ventilation were not different among the different glucose-to-lipid ratios, whatever the type of lipid. Increasing the lipid supply up to 70% of nonprotein caloric intake led to an only minor increase in lipid oxidation rate and thus to a net fat deposit. We conclude that large amounts of lipid (LCT or MCT/LCT) were not of interest in such patients.