People doing only aerobic exercise dropped weight and inches off their waistlines -- so an aerobic-only program is also a good (and less time-consuming) option, researchers said. Those in the study who just lifted weights saw very little benefit in terms of heart health, although they did gain strength.

"Aerobic plus resistance is clearly the optimal program," said Dr. Timothy Church, who studies exercise and disease at Louisiana State University's Pennington Biomedical Research Center in Baton Rouge.

The findings, are in line with other recent research and physical activity guidelines that suggest mixing in a little resistance training with regular aerobic exercise.

Researchers led by Lori Bateman of the Duke University Medical Center in Durham, North Carolina randomly assigned 196 overweight, sedentary adults to three different exercise programs.

One group did resistance training three days a week, working out on eight different weight machines to target upper and lower body muscles. A second group did two hours of aerobic training per week on gym machines -- the equivalent of about 12 miles of walking or jogging over the course of the week. The third group was assigned to do both the weight-training and aerobic-exercise programs.

More than one quarter of the exercisers dropped out of the study during the eight-month exercise programs and some others didn't have complete before-and-after health readings for researchers to compare.

In the end, Bateman and her colleagues analyzed the pre-exercise and post-exercise status of 86 participants.

On average, people in the weight-training group who completed the exercise program gained about 1.5 pounds and added a smidgen to their waistline, without changing any of their other heart or diabetes risk factors.

Those in the aerobic group lost an average of 3 pounds and half an inch from their waists.

Study participants who did both weight and aerobic training dropped about 4 pounds and 1 waistline inch. That group also saw a decrease in diastolic blood pressure (the bottom blood pressure reading) and in a "metabolic syndrome" score that reflects combined heart and diabetes risk factors.