Ethnic differences in the relationship between ectopic fat deposition and insulin sensitivity in Black African and White European men across a spectrum of glucose tolerance

Aim: To examine the hypothesis that there would be ethnic differences in the relationship between ectopic fat and tissue-specific insulin resistance (IR) across a spectrum of glucose tolerance in Black African (BA) and White European (WE) men. Materials and Methods: Fifty-three WE men (23/10/20 normal glucose tolerance [NGT]/impaired glucose tolerance [IGT]/type 2 diabetes [T2D]) and 48 BA men (20/10/18, respectively) underwent a two-step hyperinsulinaemic-euglycaemic clamp with infusion of D-[6,6-²H₂]-glucose and [²H₅]-glycerol to assess hepatic, peripheral and adipose tissue IR. Magnetic resonance imaging was used to measure subcutaneous adipose tissue, visceral adipose tissue (VAT) and intrahepatic lipid (IHL). Associations between ectopic fat and IR were assessed using linear regression models. Results: There were no differences in tissue-specific IR between ethnic groups at any stage of glucose tolerance. VAT level was consistently lower in the BA population; NGT (p = 0.013), IGT (p = 0.006) and T2D (p = 0.015). IHL was also lower in the BA compared with the WE men (p = 0.013). VAT and IHL levels were significantly associated with hepatic IR in the BA population (p = 0.001) and with peripheral IR in the WE population (p = 0.027). Conclusions: The present study suggests that BA and WE men exhibit the same degree of IR across a glucose tolerance continuum, but with lower VAT and IHL levels in the BA population, suggesting that IR may be driven by a mechanism other than increased ectopic fat accumulation in BA men.