Plasma free fatty acid turnover and oxidation during fat-free and intralipid TPN

Plasma free fatty acid (FFA) turnover and oxidation were determined by the primed continuous infusion of albumin bound (1-14C) palmitic acid in 2 patients after an overnight fast and during fat-free total parenteral nutrition (TPN), in 1 during fat-free TPN, and in another in whom one-third of calories were administered by the continuous infusion of Intralipid via a central venous catheter in conjunction with a standard glucose-amino acid solution. During TPN, plasma FFA concentrations in 2 patients were reduced from 0.7 to 0.11 and 0.08 mM, respectively, and their plasma FFA turnover during TPN was only 26% (3.86 and 2.68 mu mol/min/kg) of that prior TPN. In these subjects prior to TPN, 33 and 47% of the plasma FFA turnover was immediately oxidized, accounting for 58% of the CO2 output; however, during TPN only 16% of the plasma FFA turnover was oxidized, accounting for 10% of the caloric expenditure. The plasma FFA kinetics in the third patient were similar to those described for the first two. In contrast, the plasma FFA concentration of the fourth patient during Intralipid TPN was 0.4 mM. His plasma FFA production was 11.3 mu mol/min/kg, of which 18.4% was immediately oxidized, contributing 28% to the total CO2 output. These studies indicated that during fat-free TPN plasma FFA turnover is reduced and plasma FFA oxidation is a minor contributor to energy homeostasis; however, when one-third of the calories are supplied by fat emulsion, plasma FFA turnover is appreciable and the oxidation of plasma FFA is an important source of energy.