March 15, 2007

Belly Fat and Disease

As scientists learn more about the role of inflammation in diabetes, heart disease and other disorders, new research suggests that fat in the belly may be an important contributor to that inflammation.

Excess fat is known to be associated with disease in general, but a new study has confirmed that fat cells inside the abdomen secrete substances that increase inflammation. It is the clearest evidence yet of a link between abdominal fat and inflammation within the body.

For years, we have been aware that "apple-shaped" people, who carry fat in the abdomen, have a higher risk of heart disease, diabetes and other problems than "pear-shaped" people, who tend to store fat in the hips and thighs. Too much abdominal fat is associated with problems in the body's response to insulin. Some physicians use waist circumference to identify patients at increased risk for these problems.

It is not just any belly fat that causes inflammation, however. Back in 2004, a study found that removing abdominal fat with liposuction did not provide the same health benefits as dieting or exercising.

"Despite removing large amounts of subcutaneous fat from beneath the skin - about 20 percent of a person's total body fat mass - there were no beneficial medical effects," says Samuel Klein, M.D., the Danforth Professor of Medicine and Nutritional Science at Washington University School of Medicine in St. Louis and the senior investigator on both studies. "These results demonstrated that decreasing fat mass by surgery, which removes billions of fat cells, does not provide the metabolic benefits seen when fat mass is reduced by lowering calorie intake, which shrinks the size of fat cells and decreases the amount of fat inside the abdomen and other tissues."

'Many years ago, atherosclerosis was thought to be related to lipids and to the excessive deposit of cholesterol in the arteries,' Fontana says. 'Nowadays, it's clear that atherosclerosis is an inflammatory disease.'

In this new study, researchers looked at what is called "visceral fat" - the fat that surrounds the organs in the gut. Unlike subcutaneous fat, visceral fat is not easy to remove surgically. Since they could not take out the fat, the research team decided to analyze the blood that ran through it to determine whether or not visceral fat was somehow involved in inflammation.

As reported in the journal Diabetes, the research team found strong evidence that visceral fat contributes to systemic inflammation and insulin resistance.

"These data support the notion that visceral fat produces inflammatory cytokines that contribute to insulin resistance and cardiovascular disease," says Klein. And by contributing to inflammation, visceral fat cells in the abdomen may be doing even worse damage.

"Many years ago, atherosclerosis was thought to be related to lipids and to the excessive deposit of cholesterol in the arteries," Fontana says. "Nowadays, it's clear that atherosclerosis is an inflammatory disease. There also is evidence that inflammation plays a role in cancer, and there is even evidence that it plays a role in aging. Someday we may learn that visceral fat is involved in those things, too."

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