Lean, nondiabetic Asian Indians have decreased insulin sensitivity and insulin clearance, and raised leptin compared to Caucasians and Chinese subjects.

Objective: To study and compare the insulin sensitivity of healthy, nondiabetic Asian Indians with that of two other ethnic groups (Caucasian and Chinese) living in Singapore.

Design: Study of insulin sensitivity using euglycaemic hyperinsulinaemic glucose clamp.

Subjects: A total of 10 healthy, lean, young male subjects of each ethnic group, matched for age, body mass index (BMI) and physical activity. They all had normal glucose tolerance and had no family history of diabetes.

Measurements: Anthropometric parameters (BMI, waist-hip ratio (WHR) and percentage body fat (PBF)), fasting lipid profile and leptin concentration, insulin sensitivity index, and insulin clearance.

Results: Healthy lean (BMI 22.1+/-1.5 kg/m(2) (mean+/-s.d.)) Indians had significantly higher fasting serum leptin (5.1+/-2.5 vs Chinese 1.0+/-0.9 vs Caucasian 2.3+/-1.2 ng/ml; P<0.001), lower insulin sensitivity index (9.9+/-3.3 vs Chinese 14.1+/-3.5 vs Caucasian 18.8+/-9.2 mg/min kg fat-free mass/microU/ml; P<0.002), and lower insulin clearance (461.4+/-54.8 vs Chinese 621.0+/-99.3 vs Caucasian 646.9+/-49.2 ml/min m(2); P<0.001). Indians also had a higher PBF (26.5+/-5.2 vs Chinese 19.5+/-2.2 vs Caucasians 22.9+/-1.4%; P<0.001), diastolic blood pressure (P=0.036), fasting insulin (P<0.006) and fasting triglyceride (P=0.022). Stepwise regression analysis showed that ethnicity was the only significant independent determinant variable for the differences in insulin sensitivity index (P=0.008).

Conclusion: Healthy lean nondiabetic Indians were more insulin resistant compared to other ethnic groups despite the similarity in living environment. These findings may warrant preventive health-care strategies for type II diabetes and coronary artery disease to target Indians at an earlier stage compared to other ethnic groups.