ASSOCIATIONS BETWEEN INSULIN SENSITIVITY, AND FREE FATTY-ACID AND TRIGLYCERIDE-METABOLISM INDEPENDENT OF UNCOMPLICATED OBESITY

Insulin resistance is associated with hypertriglyceridemia and elevate d free fatty acid (FFA) concentrations in obese and diabetic individua ls, but it is unclear to what extent this relationship is independent of obesity and is present in healthy individuals. We studied 92 health y middle aged males selected from the top, middle, and lowest quintile s of the insulin sensitivity index (S-i) determined in a group of 182 men using the minimal model of glucose disappearance. Plasma FFA, trig lyceride, glucose, insulin, and C-peptide concentrations were measured during a 3-hour intravenous glucose tolerance test (IVGTT). The low-S -i (most insulin-resistant) group had more central body fat distributi on (subscapular/triceps skinfold thickness) and a higher median body m ass index (BMI) of 26.8 (range, 21.1 to 41.1) kg . m(-2) compared with the middle- and high-S-i groups with BMIs of 24.9 (19.1 to 31.5) and 23.7 (18.8 to 33.2) kg . m(-2) (P < .05). Relatively minor glucose int olerance in the low-S-i group was no longer significant when central a diposity was accounted for. Glucose tolerance was maintained by increa sed insulin secretion, leading to IVGTT insulin responses twofold and fourfold higher in the middle- and low-S-i groups, respectively, compa red with the high-S-i group (P < .01). Pasting FFA and triglyceride co ncentrations were increased in the low-S-i group relative to the other groups independent of BMI or central adiposity (P < .01). During the IVGTT, FFA decreased to similar minimum concentrations in all three gr oups. Triglyceride concentrations during the IVGTT increased above the ir minimum levels, particularly in the low-S-i group (P < .001). The i ncrease in triglyceride concentrations correlated with the incremental insulin area (r = .54, P < .001) independent of FFA and basal triglyc eride concentrations. These results are consistent with the differenti al sensitivity of the antilipolytic and glucoregulatory actions of ins ulin and support the possibility that insulin can stimulate triglyceri de release. Insulin sensitivity appears to be an important independent determinant of the variation of FFA and triglyceride concentrations i n otherwise healthy men. Copyright (C) 1994 by W.B. Saunders Company