Plus, increasing the duration and intensity of an exercise program can reduce visceral fat, according to the Duke University Medical Center researchers who conducted the trial.

The lack of regular exercise typically results in an overall weight gain of approximately four pounds per year, the researchers said.

'Situation Is Out of Balance'

Visceral fat is located deeper in the body than subcutaneous fat, which lies just under the skin. Visceral fat accumulates around the organs inside the belly. It is a particularly serious health concern, because increased levels of this form of fat have been associated with insulin resistance, cardiovascular disease and other metabolic syndromes.

"In our study, the control group that did not exercise saw a sizable and significant 8.6 percent increase in visceral fat in only six months," said Duke exercise physiologist Cris Slentz, PhD, lead author of the study.

"We also found that a modest exercise program equivalent to a brisk 30-minute walk six times a week can prevent accumulation of visceral fat, while even more exercise can actually reverse the amount of visceral fat," Slentz pointed out.

"We believe that these results shine a clear spotlight on the high costs Americans are paying for their continued inactivity," Slentz continued. "I don't believe that people in general have gotten lazier. It's more that they are working too hard or are at their desks working on computers with fewer opportunities for exercise. The situation is out of balance."

Emphasis on Prevention

The Centers for Disease Control and Prevention recommends moderate exercise consistent with the 30 minutes a day that Slentz suggests. But in light of the fact that two out of three adults are overweight or obese in the United States, Slentz believes the public-health message needs to be strengthened.

Because many dieters regain any weight they lose following "successful" short-term diets, Slentz advocates placing greater emphasis on prevention.

"It will be a challenge to change the message from 'exercise now to lose weight' to 'exercise now so in five years you won't be 20 pounds heavier,'" Slentz acknowledges.

Sedentary Men and Women

The researchers studied 175 overweight sedentary men and women who were beginning to show signs of lipid problems.

The participants were randomly assigned to one of four groups: no exercise; low dose/moderate intensity (equivalent to 12 miles of walking per week), low dose/vigorous intensity (12 miles of jogging per week) or high dose/vigorous intensity (20 miles of jogging per week).

The trial was designed solely to better understand the role of exercise. Therefore, patients were told not to alter their diet during the course of the trial. The study period ended after six months for the group that did not exercise and after eight-months for the exercise groups.

The additional two months for the exercise group came at the beginning of trial, when participants slowly ramped up their exercise to the appropriate levels.

The exercise was carried out on treadmills, elliptical trainers or cycle ergometers in a supervised setting. The researchers used computed tomography (CT) both before the exercise program began and eight months later to determine the extent and distribution of fat change.

Significant Declines

"There were no significant changes in visceral, subcutaneous or total fat in either of the low exercise groups for men or women, which suggest that this amount of exercise is adequate to prevent significant gain in fat around the stomach, and that the amount of exercise is more important than the intensity," Slentz said.

"On the other hand, participants who exercised at a level equivalent to 17 miles of jogging each week saw significant declines in visceral fat, subcutaneous abdominal fat and total abdominal fat," Slentz continued.

Participants exercising at the highest level saw a 6.9 percent decrease in visceral fat and a 7 percent decrease in subcutaneous fat.

"While this may seem like a lot of exercise, our previously sedentary and overweight subjects were quite capable of doing this amount," Slentz noted.