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

Abstract

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.

Insulin clearance as the major player in the hyperinsulinaemia of black African men without diabetes

“…Data on IHL, whole-body and hepatic insulin sensitivity, as previously reported by our group, 26,30 showed that IHL was lower in BA men, while there were no ethnic differences in hepatic insulin sensitivity or whole-body insulin sensitivity by either M value or M/I (included in Table 2 for reference).…”

“…The full methodology has been described previously 26 . In brief, a two‐step hyperinsulinaemic‐euglycaemic clamp with a stable glucose isotope infusion was used to assess whole‐body and hepatic‐specific insulin sensitivity.…”

“…We have previously shown that fasting hepatic insulin resistance in BA men with early T2D appears to be independent of IHL 25 and that there are ethnic differences in the relationship between ectopic fat accumulation and insulin sensitivity 26 . This led us to hypothesize that the role of IHL in insulin clearance may differ by ethnicity.…”

“…24 We have previously shown that fasting hepatic insulin resistance in BA men with early T2D appears to be independent of IHL 25 and that there are ethnic differences in the relationship between ectopic fat accumulation and insulin sensitivity. 26 This led us to hypothesize that the role of IHL in insulin clearance may differ by ethnicity. To our knowledge, this is the first study to examine the impact of BA ethnicity on relationships between insulin clearance, insulin sensitivity and hepatic fat in adult men of normal glucose tolerance.…”

The Link between Obesity and Inflammatory Markers in the Development of Type 2 Diabetes in Men of Black African and White European Ethnicity

“…The metabolically favourable qualities of sSAT exist due to its lower pro-inflammatory secretions as well as its ability to store excess triglycerides efficiently, thereby preventing the spill-over of free fatty acids into ectopic fat depots [ 9 ]. Our suggestion of a protective role of sSAT during obesity in BWA men may explain the lower levels of VAT and intrahepatic fat that is typically reported in black populations [ 39 , 40 , 41 ].…”