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

Abstract

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 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. 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.