The relationship between body fat distribution, insulin sensitivity and postprandial lipids in Europeans and South Asians : a cross-sectional study
Metabolic disturbances associated with central obesity and insulin resistance might underlie the higher rates of diabetes and coronary heart disease in South Asians compared with Europeans. A cross sectional study of 135 healthy South Asians and Europeans, aged 40-55 years, was performed to test whether lower insulin sensitivity in South Asians is explained by ethnic differences in body fat pattern and to establish if there are ethnic differences in postprandial triglyceride and intramyocellular lipid (IMCL) content that are associated with insulin sensitivity. Visceral fat area (VFA), measured by CT scan, was higher in South Asians than in Europeans in analyses adjusted for age, sex and body mass index (p=0.001). VFA was strongly associated with insulin sensitivity index (ISI), measured by the short insulin tolerance test, in both groups independently of total % body fat (measured by DEXA scan). In age and sex adjusted analyses ISI was 0.71 % min-1 lower in South Asians (95% CI -1.18 to -0.25, p=0.003). Adjustment for body fat pattern and triglyceride (fasting and 8 hour postprandial) reduced the ethnic difference in ISI to - 0.41 % min-1 (95% Cl -0.86 to 0.03, p=0.066). In both groups 8 hour postprandial triglyceride was highly correlated with ISI and VFA and the relationship of ISI to VFA was eliminated by adjusting for triglyceride. In a sub- study, mean IMCL content (measured by magnetic resonance spectroscopy) was higher in South Asians (p=0.046). In Europeans IMCL was correlated positively with % body fat, waist/hip ratio, VFA and negatively with ISI. In South Asians IMCL was not significantly related to ISI or obesity. We conclude that body fat pattern and IMCL cannot account for ethnic difference in insulin sensitivity. Alterations of lipid metabolism, possibly in the postprandial period, are likely to underlie the association of central obesity with insulin resistance.