That's the conclusion of a new study by Duke University Medical Center researchers. They say this "visceral fat" accumulates at a surprisingly quick rate around organs and deeper in the body than subcutaneous fat, which lies under the skin.
On the upside, the researchers found that months of regular, moderate exercise can prevent the build-up of visceral fat, while vigorous exercise can significantly reduce levels of such fat.
Researchers presented the study May 28 at the American College of Sports Medicine annual meeting in San Francisco. The study is part of a five-year Duke trial on the effects of exercise, funded by a $4.3 million grant from the National Heart, Lung, and Blood Institute.
Researchers followed 170 overweight men and women aged 40 to 65 for about eight months. The researchers divided participants into four groups.
One group did no exercise. The other three groups were classified based on a weekly exercise regimen equivalent to about 11 miles of walking, 11 miles of jogging, or 17 miles of jogging.
Lack of any exercise led to significant increases in visceral fat, the researchers found. "This finding emphasizes the high cost of continued physical inactivity for sedentary, overweight adults," they wrote.
Dr. William Kraus, a Duke cardiologist who led the exercise trial, offers simple advice to counter the buildup of visceral fat.
"Get out and do something; don't sit," says Kraus, an associate professor at Duke's medical center. "Being sedentary is very bad for your health."
It's even worse than researchers had previously realized, adds Kraus. "The most striking result was how bad the sedentary people got over eight months," he says.
Dr. Gerald Fletcher, a professor of medicine and director of preventive cardiology at the Mayo Clinic in Jacksonville, Fla., says the study illustrates well the "vicious syndrome" that results from visceral abdominal fat.
Fletcher, also a spokesman for the American Heart Association, says visceral fat buildup increases the risk of high blood pressure, blood clotting, elevated levels of "bad" cholesterol and insulin resistance, a precursor to diabetes.
While stressing the importance of exercise to prevent the intestinal fat buildup, Fletcher notes that more than two-thirds of Americans are overweight.
"I'm just hoping this study will motivate our obese public to do things we've been preaching for years," Fletcher says. "We looked at all ways to treat [visceral fat buildup], and the best way is physical activity."
Even elderly patients who had been sedentary can benefit greatly from moderate exercise, he says.
In the Duke study, for participants who did not exercise, visceral fat increased an average of 8.6 percent. Such fat decreased an average of 8.1 percent among those who did the equivalent of 17 miles' jogging weekly. Those in the two less-intensive exercise groups had no significant increase in visceral fat, demonstrating the preventive role of moderate exercise.
Men who didn't exercise averaged a 1.5 percent overall weight gain; women, 0.6 percent. However, women averaged an 11.6 percent increase in visceral fat, more than twice that of men (5.7 percent). Researchers say determining why would require further study.
Participants exercised on treadmills, elliptical trainers, or cycle ergometers in a supervised setting, and nobody changed their diet during the study.
In another Duke study, based on the exercise trial and also presented May 28 at the San Francisco sessions, researchers found the benefits of months of heavy exercise in reducing harmful cholesterol can persist even two weeks after you stop exercising.
The researchers divided 182 sedentary, overweight men and women at risk for developing diabetes or heart disease into three groups: high-amount/vigorous intensity (the caloric equivalent of 20 miles of jogging per week); low-amount/vigorous intensity (equivalent of jogging 12 miles per week); and low-amount/moderate intensity (equivalent of walking briskly for 12 miles per week).
Those in the high amount/vigorous intensity group showed improvements in HDL cholesterol (the so-called "good" form of cholesterol), HDL size and large HDL for the entire 14 days.
Previous research has shown that small HDL particles are associated with atherosclerosis and that large HDL particles help protect against the disease, the Duke researchers explain.
For tips on getting enough exercise, visit the American Heart Association. Test your knowledge of exercise and its effects on heart health by taking this online quiz by the National Heart, Lung, and Blood Institute.