Gender differences in insulin-induced free fatty acid suppression: studies in an African American population.

This study of African Americans (AA) was designed to investigate gender differences in insulin-induced free fatty acid (FFA) suppression. Sixty AA (34 women, mean age 34 +/- 7.6 years, and 26 men, mean age 30 +/- 2.9 years) participated. All subjects had an oral glucose tolerance test (OGTT). Nineteen women and 18 men also underwent a euglycemic hyperinsulinemic clamp (IC) study. Plasma insulin and FFA concentrations were obtained during both tests at 0, 60, and 120 min. While there was no gender difference in body mass index (P = 0.21), women had greater percent body fat (P < 0.001) calculated by the Siri formula. There was no gender difference in fasting FFA levels, but during the OGTT, women compared to men had significantly greater FFA suppression. Both nonobese and obese women suppressed FFA concentration by 88%, and nonobese and obese men suppressed FFA concentration by 80 and 66% respectively. This gender difference in FFA suppression was significant (P = 0.001) and independent of obesity and insulin concentration. During the IC studies, there were no gender or obesity differences in FFA suppression, with women and men suppressing FFA levels by 87-89% (P = 0.7). Fasting insulin concentrations were higher in obese vs. nonobese (P = 0.03), but fasting FFA concentrations were not different (P = 0.15). For nonobese and obese females, fasting FFA levels were 0.55 +/- 0.24 and 0.44 +/- 0.26 mEq/L, respectively, and for nonobese and obese males, 0.45 +/- 0.2 and 0.35 +/- 0.18 mEq/L, respectively. In women, development of obesity may be enhanced by greater sensitivity to insulin-induced FFA suppression as measured during an OGTT. To detect gender differences in FFA metabolism, the OGTT is superior to the IC. The lack of elevation in fasting FFA levels in obese AA women and men has not been reported in other racial groups and may indicate a greater adipocyte sensitivity to insulin in AA.