South Asians' Body Phenotype Increases Diabetes Risk

January 06, 2010

NEW YORK (Reuters Health) Jan 05 - South Asian adults have a higher fat mass and a lower lean mass compared with Chinese, European and Aboriginal adults, placing them at increased risk for insulin resistance and diabetes, researchers from Canada report.

"Body fat distribution varies among different ethnic groups, yet less is known regarding differences in lean mass and how this may affect insulin resistance," they note in the December issue of the Journal of Clinical Endocrinology and Metabolism.

This prompted Dr. Scott A. Lear of Simon Fraser University, Burnaby, British Columbia and colleagues to compare the ratio between total body fat and lean body mass in 196 Aboriginal, 222 Chinese, 202 European, and 208 South Asian adults and to examine how differences in the ratio of total body fat to lean mass might be related to levels of insulin and homeostasis model assessment (HOMA) insulin resistance.

The researchers found that South Asian men had significantly less lean mass than the other groups. On average, their lean mass was 3.42 kg less than in Aboriginal men, 3.01 kg less than in Chinese men, and 3.57 kg less than in Europeans. This finding persisted after adjustment for age, height, body build, smoking status, physical activity, diet, and other potential confounders.

Similarly, after adjusting for these confounders and for menopausal status, South Asian women had less lean mass than Aboriginal (-1.98 kg), Chinese (-2.24 kg) and European (-2.97 kg) women.

In addition, the age-adjusted total body fat to lean body mass ratio was higher in South Asian men than in Chinese and European men and higher in South Asian women than in Aboriginal, Chinese and European women (p < 0.01 for all).

"We also demonstrated that differences in total body fat to lean body mass ratios among the ethnic groups accounted for the substantial variation in insulin levels and insulin resistance," the authors report. "Importantly, higher levels of insulin and HOMA in the South Asian men and women could largely be attributed to higher total body to lean body mass ratios."

They add that the well document propensity for insulin resistance and type 2 diabetes in South Asians may be due to differences in body fat distribution.

"Interventions that reduce fat mass and increase muscle mass, such as caloric restriction and regular exercise, should be investigated in this population," Dr. Lear and colleagues conclude.

J Clin Endocrinol Metab 2009;94:4696-4702.