The results showed that people who did aerobics for eight months lost about 2.5 square inches of belly fat, as measured on a CT scan. That's about 1.5 times as much as people who did a combination of aerobic exercise and weight lifting, and about 20 times as much as those who only lifted weights.

"Resistance training is great for improving strength and increasing lean body mass," said study researcher Cris Slentz, an exercise physiologist at Duke University. But aerobic exercise is better for losing belly fat because it burns more calories, he said.

The study found that people who did both aerobic exercise and resistance training did not see further improvements to their health — in terms of liver fat, insulin resistance and other measures — beyond those who did only aerobic exercise.

Therefore, it is more time-efficient for overweight and obese people to do only aerobic exercise, the researchers said.

The truth about belly fat

Belly fat, which scientists call visceral fat, isn't what causes muffin top. Instead, it is found deep in the abdominal cavity, filling the spaces between internal organs, the researchers said.

It's considered more of a danger to health than other fat because studies have shown it is associated with higher risks of heart disease, diabetes and certain kinds of cancer.

While a combination of aerobic training and resistance training is often recommended, few studies have investigated the effects of combining the two, the researchers said.

"Our study sought to identify the most effective form of exercise to get rid of that unhealthy fat."

The study included 196 overweight, sedentary adults, ages 18 to 70, who were randomized to one of three exercise groups for eight months: aerobic training, resistance training or a combination of the two.

The aerobic group performed exercises equivalent to jogging 12 miles per week at 80 percent maximum heart rate. The resistance-training group performed eight weight-lifting exercises, doing three sets of eight to 12 repetitions of each lift, three times a week. The combination group did both of these regimens in full. The researchers closely supervised and monitored the participants to ensure maximum effort in participation.

They found that aerobic exercise was also best for reducing liver fat, too much of which can lead to nonalcoholic fatty liver disease, a leading cause of cirrhosis.

Aerobic exercise was better than resistance training at improving insulin resistance, and reducing liver enzymes and triglyceride levels — all of which are known to increase the risk of diabetes and heart disease.

"When it comes to increased health risks, where fat is deposited in the body is more important than how much fat you have," Slentz said.

Aerobic training burned 67 percent more calories than resistance training in the study.

How much exercise do we really need to do?

While the training programs in the study were rigorous, previous research suggests that results could be achieved with a more moderate aerobic exercise program, Slentz said

"What really counts is how much exercise you do, how many miles you walk and how many calories you burn," he says. "If you choose to work at a lower aerobic intensity, it will simply take longer to burn the same amount of unhealthy fat."

The study will be published in an upcoming issue of the American Journal of Physiology Endocrinology and Metabolism.

Pass it on: Aerobic exercise is better than weight lifting at reducing belly fat.