Diminished plasma free fatty acid clearance in obese subjects

Obese subjects were compared with lean subjects to define the previously reported disturbance of plasma free fatty acid (FFA) kinetics in terms of altered net transport (lipolysis) or clearance (esterification). These measurements were made during prolonged constant infusions of 1--14C-palmitate toward the end of sustained glucose ingestion and again 6-8 hr after stopping glucose. Net transport of FFA was suppressed to equally low levels in obese and lean subjects, though at the expense of higher insulin concentrations in the obese. Whereas in the lean subjects the clearance of FFA was significantly stimulated with glucose, the obese subjects showed low clearance rates both during and after stopping glucose. When glucose was stopped, net transport rose more rapidly and to a greater extent in some obese than in the lean subjects. The increased influx of FFA led to a rise in the plasma triglyceride level only in the lean subjects. These studies suggest that clearance of plasma FFA, probably denoting esterification in tissues such as muscle and adipose tissue, is impaired in obesity and cannot be readily stimulated with glucose and insulin. Lipolysis, measured as net transport of FFA, however, is suppressible with glucose and insulin in the obese, though this might be achieved only at insulin levels that are higher than those in lean subjects.