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Belly Fat Is Key to U.S. Diabetes Risk

Researchers Say Hefty Waist Sizes Explain Higher Diabetes Rate in U.S. Than in England

By Salynn Boyles
WebMD Health News

Reviewed by Laura J. Martin, MD

Oct. 7, 2010 -- Middle-aged Americans tend to have more belly fat than their English counterparts, and the difference may explain the higher diabetes rate in the U.S. compared to England.

Investigators with the University College London and the nonprofit research group RAND Corporation first reported on health differences between older Americans and people in England in 2006, finding diabetes incidence in the U.S. to be twice as high as in England.

RAND Corporation senior economist James P. Smith, PhD, says even though more people in the U.S. are obese than in England, this did not fully explain the difference in diabetes prevalence.

"In fact, obesity and body mass index (BMI) explained very little of the difference," Smith tells WebMD.

When the researchers further explored the issue, they concluded that belly fat was largely to blame for the higher diabetes incidence in the U.S., especially among women.

On average, waist sizes among the American women included in the study were 5 centimeters larger than their peers in England. American men had waists that averaged 3 centimeters larger than Englishmen.

Even middle-aged and older Americans who were not considered overweight tended to have larger waists than their English peers.

The researchers analyzed data from nationally representative health surveys conducted in the U.S. and in England. The analysis included people between the ages of 52 and 85.

They did not find big differences between the two countries in well-recognized risk factors for diabetes.

Americans included in the analysis had slightly higher BMIs and they were slightly older, while the English smoked more and tended to have less formal education.

"There was not enough difference in these traditional diabetes risk factors to explain the difference we saw," Smith says.

The only major difference between the two groups was waist size. Americans tended to have larger waists, whether their BMI scores put them in the normal, overweight, or obese category.

For example, one in four normal-weight women in the U.S. survey had enough belly fat to put them in the high-risk category, compared to roughly one in 10 women in England.

The findings suggest that BMI is a poor predictor of diabetes risk in people over 50, Smith says.

"Waist size may be much more important than BMI at the age when people are most likely to develop type 2 diabetes," he says.

So why do Americans have more belly fat than the English?

The reasons for this are not clear. But as with most things related to weight and health, diet and exercise probably play a big role.

Eating a high-fat diet and not exercising are risk factors for belly fat. People in the U.S. tend to eat higher-fat diets than people in the England, and they exercise less.

Gerald Bernstein, MD, who directs the Friedman Diabetes Institute at Beth Israel Medical Center in New York City, says people in the U.S. typically walk half as much over the course of a day as people in Europe -- about 5,000 steps compared to 10,000.

Bernstein says fat that accumulates in the belly is particularly dangerous because it affects the organs involved in regulating blood sugar.

Insulin stimulates the liver to store sugar in the blood for later use. Belly fat keeps the liver from doing this efficiently, so blood sugar accumulates in the bloodstream.

"Exercising helps the body burn this fat, but it is not enough," Bernstein tells WebMD. "People who have excess fat around the middle need to do all they can to reduce their waist size. That means exercising, eating a healthy diet, and cutting calories."

SOURCES: Smith, J.P. Journal of Epidemiology and Community Health, published online Oct. 7, 2010.James P. Smith, PhD, senior economist, RAND Corporation.Gerald Bernstein, MD, director, diabetes management program, Gerald J. Friedman Diabetes Institute, Beth Israel Medical Center, New York City.News release, RAND Corporation.

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