Ethnicity determines how body stores fat: study

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August 23, 2007  
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obese chinese kidsCM NEWS - A groundbreaking study has “definitively” verified that ethnicity determines where the body stores fat. Chinese and South Asian tend to deposit more fat to their internal organs per kilogram of total body fat than Europeans do. This implies that some ethnicities, particularly those of Chinese or South Asian descent, face higher risks for diseases related to obesity.

Dr. Scott Lear, Assistant Professor in the School of Kinesiology at Simon Fraser University and Canadian Obesity Network Investigator led the team that discovered Chinese and South Asians have more dangerous abdominal fat than Europeans, putting them at greater risk for heart disease, high blood pressure, diabetes and other complications.

Genetic factor is highly possible to be at play, but further study is needed to confirm the theory, Dr. Lear told Ming Pao Vancouver.

As well, Lear’s research suggests current measuring techniques for healthy body fat are not as accurate when used in those ethnic populations, leading to difficulty in diagnosis and treatment.

Previous studies have reported that those of Chinese and South Asian origin have more body fat at a given BMI than do Europeans. Data suggest that Aboriginals, Chinese, and South Asians have more risk factors for type 2 diabetes and cardiovascular disease than do Europeans at the same body mass index [BMI; calculated as weight in kilograms divided by height in meters squared (kg/m2)] or waist circumference.

In China, the prevalence of overweight has increased nearly 50% in a 10-year period. The number of overweight population in China is estimated at about 200 million. In India the rate of obesity is estimated to be 7.0–13.3% in men and 15.6–23.7% in women. In addition, as those of Chinese and South Asian origin move from rural to urban to Western environments, the prevalence of obesity increases.

Dr. Lear’s team compared the relation between abdominal adipose tissue and total body fat between 822 persons living in Canada of Aboriginal, Chinese, and South Asian origin with persons of European origin. Total abdominal adipose tissue (TAT), subcutaneous abdominal adipose tissue (SAT), visceral adipose tissue (VAT), total body fat mass, lifestyle, and demographics were assessed. Relations between BMI and total body fat, TAT, SAT, and VAT and between total body fat and TAT, SAT, and VAT were investigated.

What is adipose tissue? Adipose tissue or fat is loose connective tissue composed of adipocytes. Its main role is to store energy in the form of fat, although it also cushions and insulates the body. Obesity in humans and most animals is not dependent on the amount of body weight, but on the amount of body fat—specifically adipose tissue.

Abdominal fat is composed of abdominal subcutaneous fat and intraabdominal fat. Intraabdominal adipose tissue is composed of visceral, or intraperitoneal, fat, mainly composed of omental and mesenteric fat and retroperitoneal fat masses by a delineation along the dorsal borderline of the intestines and the ventral surface of the kidney.

Why measuring visceral adipose tissue? Assessment of body fat distribution, particularly visceral adipose tissue, is important for accurate risk evaluation for cardiovascular diseases. The amount of adipose tissue stored in the intraabdominal cavity is a crucial and independent risk factor for heart attack.

Waist circumference is a viable way to measure abdominal visceral adipose tissue mass. A waist circumference greater than 100 cm is most likely to be associated with disturbances in lipoprotein metabolism and in plasma glucose-insulin homeostasis. Waist circumference is a convenient and simple measurement that determines the extension of abdominal obesity, which appears closely linked to abdominal visceral adipose tissue deposition.

Dr. Lear’s study found that, adjusted for age, BMI, and total body fat, Aboriginal, Chinese, and South Asian men and women had greater amounts of VAT than did the European men and women. With further adjustment for sex, maximal education, humerus breadth, smoking status, and physical activity, the study was able to determine that ethnic background was a significant modifier of the relation between VAT and total body fat, i.e., Chinese and South Asian backgrounds are determinants of discrete regions of abdominal adiposity.

“We found that Chinese participants had a greater SAT and VAT than did European participants and that most South Asians had more TAT, SAT, and VAT than did the Europeans,” the study says. “These differences were more marked for VAT, which is more strongly associated with diabetes and cardiovascular disease risk factors than are other regions of adipose tissue.”

The researchers suggest that the Chinese and South Asian participants possibly deposited more VAT per kilogram of total body fat than did the Europeans. These results are particularly important because of the increasing prevalence of obesity in Asian populations.

In contrast, no difference was observed in the distribution of body fat between Aboriginals and Europeans.

“We now have definitive proof that current targets for waist circumference and body mass index measurements used by physicians, which were developed based on Caucasian populations, are not able to accurately determine health risks in these groups,” Lear explains. “Clearly, we can no longer use a ‘one-size-fits-all’ approach to diagnosing these serious medical conditions.”

Lear says that new guidelines are urgently needed to properly screen these groups.

“Canada’s population is increasing, and many of our new immigrants are coming from China and South Asia. We need to be able to identify risks at an early stage, or we will see increased healthcare costs and mortality in the future.”

The project was funded by the Canadian Institutes of Health Research’s Institute for Nutrition, Metabolism and Diabetes.

[Am J Clin Nutr 2007;86:353–9]