Context: Body fat distribution varies among different ethnic groups, yet less is known regarding differences in lean mass and how this may affect insulin resistance.

Objective: Our objective was to compare total body fat to lean mass ratio (F:LM) in Aboriginal, Chinese, European, and South Asian individuals with differences in insulin resistance.

Participants, Design, and Setting: Aboriginal (196), Chinese (222), European (202), and South Asian (208) individuals were recruited across a range of body mass index to participate in this cross-sectional community study.

Main Outcome Measures: Total body fat, lean mass, and insulin resistance were assessed using homeostasis model assessment (HOMA).

Results: After adjustment for confounders and at a given body fat, South Asian men had less lean mass than Aboriginal [3.42 kg less; 95% confidence interval (CI) = 1.55–5.29], Chinese (3.01 kg less; 95% CI = 1.33–4.70), and European (3.57 kg less; 95% CI = 1.82–5.33) men, whereas South Asian women had less lean mass than Aboriginal (1.98 kg less; 95% CI = 0.45–3.50), Chinese (2.24 kg less; 95% CI = 0.81–3.68), and European (2.97 kg less; 95% CI = 1.67–4.27) women. In adjusted models, F:LM was higher in South Asian compared with Chinese and European men and higher in South Asian compared with Aboriginal, Chinese, and European women (P < 0.01 for all). Insulin and HOMA were greatest in South Asians after adjustment; however, these differences were no longer apparent when F:LM was considered.

Conclusions: South Asians have a phenotype of high fat mass and low lean mass, which may account for greater levels of insulin and HOMA compared with other ethnic groups.