DALLAS — By just lifting weights twice a week for an hour, women can battle the buildup of tummy fat that often takes hold with aging, a new study suggests.

And they didn't even diet.

The study focused on intra-abdominal fat, the deep fat that wraps itself around organs and is the most unhealthy because it's linked with heart disease.

"One of the most common complaints in women, especially as we continue to age, especially as we go through menopause, the No. 1 complaint is abdominal growth," said Dr. Tracy Stevens, a cardiologist who directs the women's heart center at St. Luke's Hospital in Kansas City.

"It's the apple-shaped person I'm most worried about," said Stevens, who was not involved in the study. "The more central the fat, the more it's laid down in the arteries."

The study was funded by the National Institutes of Health and is being presented Friday at an American Heart Association conference in Phoenix.

In it, 164 overweight and obese Minnesota women ages 24 to 44 were divided evenly into two groups. One group participated in a two-year weight-training program and the other was simply given a brochure recommending exercise of 30 minutes to an hour most days of the week. Both groups were told not to change their diets in a way that might lead to weight changes.

Women who did the weight-training for two years had only a 7 percent increase in intra-abdominal fat, compared to a 21 percent increase in the group given exercise advice.

The strength-training group also decreased body fat percentage by almost 4 percent, while the group just given advice remained the same.

"I think we need to provide people with multiple possibilities, multiple roads to the same end. If this is what you're willing to do, I'll tell you what you can get out of it," said the lead author of the study, Kathryn Schmitz, an epidemiologist at the school of medicine at the University of Pennsylvania.

Researchers reported only marginal effects from the training on total fat mass and the fat you can pinch under the skin.

Using both free weights and machines, the women in the strength-training group worked out for about an hour and were encouraged to gradually increase the weights they lifted.

"This is not a program you could do in your home, unless you can afford to have a full gym in your basement," Schmitz said.

The women, who completed 70 percent of the advised exercise throughout the study, were in supervised strengthening classes for 16 weeks.

Schmitz said the focus was on chest, back, shoulders, biceps, triceps, lower back, buttocks and thighs. She noted that adding muscle mass can help overweight women move faster so they burn more calories.

Dr. Rita Redberg, a cardiologist at the University of California San Francisco, pointed out that since muscle burns more calories than fat, increasing muscle mass means losing more calories.

"Certainly, any kind of exercise is better than not doing anything," Redberg said. But for "maximal benefit, cardio with weight training will get a lot more bang for your buck."

"I think exercise is the fountain of youth," she said. "If it was a pill, everyone would be taking it."