Visceral adipose tissue is not increased in Pima Indians compared with equally obese Caucasians and is not related to insulin action or secretion

Pima Indians are insulin resistant and hyperinsulinaemic compared with Cauc asians. We investigated whether abdominal fat distribution was different be tween Pimas and Caucasians and whether differences in the amount of viscera l fat explained metabolic differences between the groups. Total body fat (a bsorptiometry) and abdominal fat distribution at L4-L5 (magnetic resonance imaging) were compared in 20 Pima Indians (10 men/10 women) and 20 age-, se x- and BMI-matched Caucasians. Insulin action was measured as glucose dispo sal during a two-step hyperinsulinaemic-euglycaemic glucose clamp and insul in secretion was assessed in response to oral and intravenous glucose toler ance tests. By design, percent body fat was similar in Pimas and Caucasians . Abdominal visceral and subcutaneous adipose tissue areas were also simila r in the two groups (151 +/- 16 vs 139 +/- 15 cm(2) and 489 +/- 61 vs 441 /- 57 cm(2) respectively). Plasma insulin concentrations were higher in Pim as than Caucasians in the fasting state (27 +/- 6 vs 11 +/- 2 mU/ml; p < 0. 01) and after a 75-g oral glucose load (area under the curve 19975 +/- 2626 vs 9293 +/- 1847 mU.l(-1) 180 min(-1); p < 0.005). Glucose disposal was lo wer in Pimas than Caucasians during both steps of the clamp and negatively correlated (after adjustment for percent body fat and sex) with visceral ad ipose tissue in Caucasians (partial r = -0.51, p = 0.03), but not in Pima I ndians (r = -0.03, p = 0.92). Insulin secretion was not related to visceral fat independently of percent body fat in either group. We conclude that a relative increase in visceral fat does not explain insulin resistance and h yperinsulinaemia in Pima Indians.