Independent association of insulin resistance with larger amounts of intermuscular adipose tissue and a greater acute insulin response to glucose in African American than in white nondiabetic women

Background: African Americans (AAs) have a higher prevalence of obesity and type 2 diabetes than do whites. Higher insulin resistance and hyperinsulinemia have been reported in adult AAs than in whites. Differences in adipose tissue and its distribution may account for these findings. Objective: The objective was to ascertain whether differences between AA and white women in adipose tissue (AT) and skeletal muscle (SM) volumes account for ethnic differences in insulin resistance. Design: We used whole-body magnetic resonance imaging to measure AT and SM volumes and used the intravenous-glucose-tolerance test to measure insulin resistance. Results: AAs (n = 32) were 29-42% more insulin resistant than were whites (n = 28) after adjustment for weight and height or any AT volumes (P < 0.05). After adjustment for SM volume, the difference decreased to 19% and became nonsignificant. AAs had a 163% greater acute insulin response to glucose than did whites; this difference was significant even after adjustment for insulin sensivitity index, weight, height, and any magnetic resonance imaging measures. With respect to regional AT volumes, an association independent of race, weight, height, and SM volume was found only between increased intermuscular AT and lower insulin sensitivity index. Conclusions: Premenopausal AA women had significantly higher insulin resistance and acute insulin response to glucose than did their white counterparts. Whereas the difference in insulin resistance was partially accounted for by a greater SM volume in the AAs than in the whites, the difference in the acute insulin response to glucose was independent of any AT and SM measures and was disproportionately larger than expected according to the difference in insulin resistance. In addition, whole-body intermuscular AT was an important independent correlate of insulin resistance.