Objective: To determine the extent to which gender differences in the rate of insulin-mediated glucose disposal are influenced by differences in body fatness.
Design: A cross-sectional study of a biracial sample of men and women drawn from a population-based study.
Subjects: Twenty-five 25-44 year old residents of Dade County, FL. Twenty-five African-Americans (14 men and 11 women) and 28 white, nonHispanics (15 men and 13 women). All participants were free of diabetes mellitus (WHO Criteria).
Measurements: All persons volunteered to undergo a hyperinsulinemic euglycemic clamp procedure to determine the rate of insulin-mediated glucose disposal (insulin sensitivity, M). Several measures of body fatness were quantified and the percentage body fat determined according to published equations.
Results: Men and women had similar unadjusted M values. Within each gender and ethnic group M was inversely related to percentage body fat (r = -0.55 to -0.84; p < 0.05). After adjustment for percentage body fat, women were more insulin sensitive than men (10.1 vs 5.1 mg/kg/min among African-Americans and 10.1 vs 6.9 mg/kg/min among white, nonHispanics; p < 0.05 for each). When M was expressed per unit of fat free mass, women were still significantly more insulin sensitive than men (p < 0.05 for each ethnic group). In multivariate analyses, gender and percentage body fat were independently related to M in both ethnic groups accounting for 70% of the variance among African-American participants and 34% of the variance among white nonHispanic participants.
Conclusion: The similar M values between men and women despite the higher percent body fat among women indicate that women are more insulin sensitive in muscle tissue than men. This was substantiated when M was normalized for fat free mass. This 'insulin advantage' may be related to the lower risk of coronary disease experienced by women and the loss of this advantage may in part underlie the stronger deleterious effects of diabetes that women suffer.