Fat oxidation and plasma removal capacity of an intravenous fat emulsion in elderly and young men

ObjectiveWe explored metabolic and thermogenic responses to exogenous fat in relation to age as a basis for a rational design of parenteral nutrition in elderly patients.MethodsTen healthy elderly men (70–78 y of age, body mass index 21–27 kg/m2) and 10 healthy young men (19–45 y of age, body mass index 19–26 kg/m2) were studied with a hypertriglyceridemic clamp (primed infusion of a long-chain triacylglycerol emulsion to reach and stabilize at a triacylglycerol concentration of 4 mmol/L for 180 min). Continuous indirect calorimetry was carried out in the basal state and throughout the study period.ResultsThe infusion rates required to maintain plasma triacylglycerol levels at 4 mmol/L were similar in elderly and young individuals (mean ± SEM 0.201 ± 0.027 versus 0.203 ± 0.014 mmol/min, not significant). Plasma concentrations of free fatty acids and β-OH-butyrate were higher in the elderly before the infusion and increased in a similar manner in both groups during infusion. Energy expenditure at baseline was higher in the young than in the elderly (79 ± 2 versus 64 ± 3 kcal/h; P < 0.001), although the respiratory quotient was similar in the two groups (0.80 ± 0.01 versus 0.78 ± 0.01, not significant). During lipid administration there was a similar increase in energy expenditure in the old and young individuals (+9.0 ± 1.3% versus +6.0 ± 1.8%, not significant). Lipid infusion resulted in similar increments in fat oxidation in the young and elderly (23.9 ± 7.0% versus 15.1 ± 4.9%, respectively, not significant). Plasma lipoprotein lipase activity was almost three times higher in the young than in the elderly subjects (0.23 ± 0.02 versus 0.65 ± 0.09 mU/mL, respectively, P < 0.001). During lipid infusion, a similar increment (four- to five-fold) in plasma lipoprotein lipase activity was noted in the two groups.ConclusionsElderly healthy men have a similar capacity as young healthy men to clear and oxidize a high triacylglycerol load administered as a hypertriglyceridemic clamp.