TIME COURSE OF PLASMA-FREE FATTY-ACID CONCENTRATION IN RESPONSE TO INSULIN - EFFECT OF OBESITY AND PHYSICAL-FITNESS

This study examines the relationships between parameters of the time course of plasma free fatty acid (FFA) concentration during a euglycemic, hyperinsulinemic clamp (100 mU/m2 · min) and the age, body composition, and physical fitness, indexed as maximal aerobic capacity (Vo2 max), of three groups of healthy men: (A) 20 obese older men (32% ± 1% fat, aged 60 ± 2 years, mean ± SEM); (B) 11 lean older men (19% ± 1% fat, aged 63 ± 2 years); and (C) 11 lean younger men (16% ± 2% fat, aged 27 ± 2 years). The time course was modeled as a delayed exponential decline from an initial level to a plateau level. The plateau level was 72% ± 2%, 72% ± 2%, and 68% ± 3% of the initial level in groups A, B, and C, respectively. The delay was shorter in the younger men than in the older men (7.6 ± 0.9 minutes in group C v 13.2 ± 1.0 in group A and 11.9 ± 1.6 minutes in group B), but correlated more strongly with percent fat, waist to hip ratio (WHR), or Vo2max than with age. The magnitude of the rate constant of the exponential, k, was smaller in obese than in lean men (3.2 ± 0.2 h-1 in group A v 5.3 ± 0.6 h-1 in group B and 6.4 ± 0.6 h-1 in group C), and was independently predicted only by percent fat in the older men and only by Vo2max when the older and younger groups were combined. Longer delays and smaller values of k were associated with insulin resistance, indexed either as a high fasting plasma insulin concentration (IRIo) or as a low glucose disposal rate during the clamp. These results indicate that resistance to the action of insulin in both FFA metabolism and glucose metabolism occurs with obesity and decreased physical fitness. © 1992.