old culture, new fat
by Megan Miller

he aborigines of Australia, members of one of the world's most ancient living cultures, have survived for thousands of years in the harshest landscapes. But now their existence is threatened by a modern, Western-borne condition — obesity. A recent study shows that obesity-related diseases such as diabetes pose an especially potent threat to the health of aborigines, a population that now has one of the highest rates of diabetes in the world.

The study was conducted by Mark Daniel, assistant professor of health behavior and health education and of epidemiology in the School of Public Health, in collaboration with Australian researchers. It included 2,626 people aged 15 years and older in 15 communities in central and northern Australia. The researchers traveled to these isolated communities to gather information on subjects' weight, height, and blood glucose levels.

Weight and height were used to calculate an individual's body mass index (BMI), a score used to estimate fat mass and classify individuals into categories such as overweight or obese. Because high BMI is the strongest known risk factor for diabetes, the researchers used statistical tests to determine which categories of BMI were associated with an elevated risk of having the disease.

The researchers found that the prevalence of diabetes had reached epidemic proportions, with an estimated 15 percent of the aboriginal population studied showing signs of the disease. They also found that aborigines had a higher risk of diabetes at levels of BMI below the international guidelines used to classify overweight and obesity — in other words, within the range of what has been considered a healthy weight in the past.

Guidelines for BMI, expressed as weight adjusted for height in units of kilograms per meters squared, define several levels of risk: 20 to 24.9 as healthy, 25 to 29.9 as overweight, and 30 or higher as obese. In this population, researchers found that a BMI of as low as 22 kg/m2 was associated with an increased risk of diabetes. For aborigines, it appears that the level of overweight associated with diabetes is set lower, meaning that modest gains in body fat may translate into a substantial increase in diabetes risk.

"If we could prevent the development of BMI greater than twenty-two kilograms per meters squared, we could, in theory, prevent forty-six percent of the diabetes cases," Daniel says.

aniel cautions that more research is needed before recommending revision of the BMI guidelines. But, for now, the study strengthens the point raised by other studies: making BMI guidelines population specific may make them more useful tools for disease prevention.

But why has diabetes hit these aboriginal communities so hard in a relatively short period of time — during the past 40 to 50 years, within the span of only a few generations? Daniel cites environmental factors such as forced relocation, discrimination, poor access to resources such as health care, and limited life opportunities coupled with psychosocial stress. He adds that a loss of traditional ways and adoption of Western diet and physical activity patterns also contribute. "People are learning ways of living that are extremely unhealthful," he says.

The popular press, on the other hand, has presented a different interpretation of the study's findings, one that Daniel sees as misguided in its emphasis on racial differences. "The media has spun this story to say that minority populations are at high risk for diabetes, which makes the disease outcome a problem of people of color or minority status, rather than of the position of these groups vis-à-vis the greater society. Such populations definitely have higher rates of diabetes, and in that sense, are at greater 'risk,' but that doesn't necessarily mean that it's because of their genes," Daniel says. The complex interaction among environment, genetics, and behavior in indigenous populations may hold the key to understanding why chronic diseases such as diabetes are on the rise. Daniel and colleagues are developing programs with aboriginal communities in Australia to reduce diabetes cases through attempts to limit excessive gains in BMI, based on the results of this study. But more basic research remains. Daniel and other researchers have yet to study diabetes risk in urban aborigines — a population that appears to suffer even more from the disease than their rural counterparts.

This study appeared in the July 2002 issue of Diabetes Research and Clinical Practice and was funded by the National Health and Medical Research Council of Australia and the Medical Research Council of Canada.

Megan Miller is a recent graduate of the department of nutrition in the school of public health at Carolina.