WASHINGTON (AFP) -- Weight gain can be more dangerous for South Asians than for Caucasians because the fat clings to organs like the liver instead of the skin, said a study published Thursday.

The main difference between Caucasians and South Asians comes down to how much space there is to store fat in the body and where it holes up, said Sonia Anand, lead author of the study in the public access journal PLoS One.

"South Asians have less space to store fat below the skin than white Caucasians," said Anand, a professor of medicine and epidemiology at McMaster University.

"Their excess fat, therefore, overflows to ectopic compartments, in the abdomen and liver where it may affect function."

When extra fats clings to the organs, it can cause high glucose and lipid levels, which are risk factors for heart disease.

That means South Asians with a weight and height ratio, or body mass index (BMI), that would be considered in the healthy range for Caucasians may merit screening for conditions like diabetes and coronary artery disease.

The Canada-based study recruited 108 people in all, some first- or second-generation immigrants from India, Pakistan, Sri Lanka, or Bangladesh and the rest Caucasian subjects whose ancestry could be traced to Europe.

They underwent a series of measurements and tests to assess body fat, cholesterol and sugar levels.

"Young, apparently healthy South Asians have greater metabolic impairment compared to white Caucasians who tend to develop metabolic changes at higher levels of obesity and at a more advanced age," said the study.

South Asians tended to have lower HDL (or good) cholesterol, higher total body fat but lower levels of abdominal fat, fattier livers and less lean muscle mass than Caucasians of similar age, height and weight.

"This study helps explain why South Asians experience weight-related health problems at lower BMI levels than Caucasians," said Arya Sharma, director of the Canadian Obesity Network and a co-author of the study.

"For the clinician, this also means that individuals of South Asian heritage need to be screened for the presence of heart disease and diabetes at lower BMIs."