Their study of overweight, sedentary adults found that those who started working out on treadmills and stationary bikes tended to lose, or at least not add to, their stores of visceral fat -- fat that accumulates around the abdominal organs.

In contrast, their peers who remained sedentary showed a substantial gain in visceral fat over just 6 months, according to findings published in the October issue of the Journal of Applied Physiology.

While this deep abdominal fat may not make itself apparent in the form of a spare tire, it is linked to a number of ill health effects, including a higher risk of type 2 diabetes, high cholesterol and heart disease.

The new findings show that even moderate exercise, such as brisk walking, may put the brakes on visceral fat accumulation, according to Dr. Cris Slentz, an exercise physiologist at Duke University Medical Center in Durham, North Carolina, and the lead author of the study.

What's more, study participants who got the most exercise -- the equivalent of jogging 20 miles per week -- shed both visceral fat and the superficial layers of abdominal fat that make for love handles.

The intensity of the exercise did not seem to matter as much as the amount, Slentz stated. Study participants who exercised moderately -- the equivalent of brisk walking -- for about 3 hours each week did just as well as those who worked out more vigorously for 2 hours a week. Overall, both groups showed no significant gain in abdominal fat.

The study group that exercised the hardest -- at the intensity level of jogging, for 3 hours each week -- saw an average decline of 7 percent in both visceral fat and more superficial abdominal fat. In contrast, participants in the fourth study group, who maintained their sedentary ways, saw a gain in visceral fat of nearly 9 percent over 6 months.

For the most part, the exercisers worked out on gym equipment like treadmills and exercise bikes.

The bottom line, according to Slentz, is that inactivity comes at the "high cost" of rapid fat accumulation, while regular exercise can at least prevent such an increase. In a culture that values quick results, he said, the idea of maintaining what you have is a "hard sell."

But long-term weight maintenance, as opposed to repeated yo-yo dieting, is a worthy goal, according to Slentz. Exercise now, he said, and you might not be "20 pounds heavier in five years."

However, he pointed out, "The million-dollar question with exercise is how to get people to do it long-term."

Moderate exercise in this study -- walking for about 3 hours a week -- was enough to prevent fat gain, and it is in line with health officials' advice for all adults to fit in 30 minutes of moderate activity on most, if not all, days. That's a level of exercise most people can achieve, Slentz noted.

"We eat everyday," he said. "So we should we walk everyday."

SOURCE: Journal of Applied Physiology, October 2005.

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