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

OBJECTIVE: We 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. METHODS: Ten healthy elderly men (70-78 y of age, body mass index 21-27 kg/m(2)) and 10 healthy young men (19-45 y of age, body mass index 19-26 kg/m(2)) 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. RESULTS: The 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 beta-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. CONCLUSIONS: Elderly healthy men have a similar capacity as young healthy men to clear and oxidize a high triacylglycerol load administered as a hypertriglyceridemic clamp.