Researchers discovered that aerobic training, such as jogging or swimming, is best at both burning fat and helping people lose weight. (Darryl Dyck/Canadian Press)

Aerobic exercise is the best form of activity to burn fat when compared to resistance training and a combination of the two, according to researchers at Duke University.

Their study, published in the Journal of Applied Physiology, is the largest randomized trial to monitor changes in body composition from the three modes of exercise in obese and overweight adults without diabetes.

“We want to offer clear, evidence-based exercise recommendations that will truly help people lose weight and body fat," said lead author Leslie Willis, an exercise physiologist at Duke Medicine in Durham, N.C.

Researchers were concerned with recent exercise guidelines recommending resistance training such as weightlifting as a means of helping people lose weight by increasing their resting metabolic rate. While resistance training is great for creating muscle mass and improving sugar levels, the studies on its effect on fat mass have been inconclusive.

As a result, researchers wanted to compare resistance with aerobic training such as running, swimming or walking.

They started with 234 overweight or obese adults who were randomly assigned one of three exercise regimens:

• Resistance training three days per week, three sets of weightlifting per day, eight to 12 repetitions per set.
• Aerobic training, about 19 kilometres per week.
• Combination: resistance training three days per week, three sets per day, eight to 12 repetitions per set, plus about 19 kilometres per week of aerobic exercise.

All exercise was supervised and in the end, 119 participants completed the study.

According to the researchers' findings, those who only did resistance training did not lose weight. They gained muscles, which did make them weigh more, and they did not reduce their fat mass.

The participants in the combined group lost weight but not a lot of fat mass.

The bottom line, say the researchers, is that aerobic activity, overall, helped people lose both weight and fat mass significantly.

"Our study suggests that aerobic exercise is the best option for reducing fat mass and body mass," said study co-author Cris A. Slentz, a Duke exercise physiologist.

"It’s not that resistance training isn’t good for you; it’s just not very good at burning fat."

The authors of the study emphasized that weight training is important for older adults to reduce muscle atrophy but not as important for younger people.