Differences in the link between insulin sensitivity and ectopic fat in men of Black African and White European ethnicity

Objectives: In men of black west African (BAM) and white European (WEM) ethnicity, we aimed to (1) compare adipose tissue, peripheral and hepatic insulin sensitivity and (2) investigate associations between ectopic fat and insulin sensitivity by ethnicity. Design and methods: In overweight BAM (n = 21) and WEM (n = 23) with normal glucose tolerance, we performed a two-step hyperinsulinaemic-euglycaemic clamp with infusion of [6,6 ²H₂]-glucose and [²H₅]-glycerol to measure whole body, peripheral, hepatic and adipose tissue insulin sensitivity (lipolysis). Visceral adipose tissue (VAT), intrahepatic lipids (IHL) and intramyocellular (IMCL) lipids were measured using MRI and spectroscopy. Associations between insulin sensitivity and ectopic fat were assessed using Pearson's correlation coefficient by ethnicity and regression analysis. Results: There were no ethnic differences in whole body or tissue-specific insulin sensitivity (all P > 0.05). Suppression of lipolysis was inversely associated with VAT and IHL in WEM but not BAM (VAT: WEM r = −0.68, P < 0.01; BAM r = 0.07, P = 0.79. IHL: WEM r = −0.52, P = 0.01; BAM r = −0.12, P = 0.63). IMCL was inversely associated with skeletal muscle insulin sensitivity in WEM but not BAM (WEM r = −0.56, P < 0.01; BAM r = −0.09, P = 0.75) and IHL was inversely associated with hepatic insulin sensitivity in WEM but not BAM (WEM r = −0.53, P = 0.02; BAM r = −0.13, P = 0.62). Conclusions: Ectopic fat deposition may play a lesser role in reducing insulin sensitivity in men of black African ethnicity and may not be driven by lipolysis. Resistance to storing VAT, IHL and IMCL may enable men of black African ethnicity to maintain comparable insulin sensitivity to white Europeans.