All exercise is not the same. According to a new study, if you want to lose weight and body fat, your exercise regimen should focus on aerobic exercise, rather than resistance or weight training.

When developing an exercise plan, the best ratio of aerobic training to resistance training really depends on your individual fitness goals, Leslie Willis, lead author of the study, tells The Doctor.

Most people have a certain amount of time per week for working out, and have to decide how to spend that time.“ If it’s a person that is overweight or obese, and losing fat and weight is the target goal, we would suggest adding extra aerobic training, not resistance training, to the regimen, ” says Willis, a researcher in the department of cardiology at Duke University Medical Center.

The aerobic exercise group trained for about 133 minutes a week and lost weight, while the resistance training group exercised for about 180 minutes and did not lose weight.

That is not to say resistance training is bad. On the contrary, research clearly shows that older persons may benefit from resistance training. It improves their mobility and balance, Willis says. Older persons who are experiencing muscle atrophy benefit from resistance training because it builds lean muscle mass, which is lost as people age.

The study looked at 234 overweight or obese adults between 18 and 70 years old. Participants were randomly assigned to one of three groups: resistance training, aerobic training, or aerobic and resistance training. The investigators found that people in the aerobic training and aerobic plus resistance training groups lost more weight than those who practiced resistance training alone. Those in the resistance training group actually gained weight because their lean body mass increased – not in and of itself a bad thing.

Aerobic exercise was also a more efficient way to lose body fat, compared to resistance training. The aerobic exercise group trained for about 133 minutes a week and lost weight, while the resistance training group exercised for about 180 minutes and did not lose weight. "Our results suggest that the aerobic and resistance training combo group outperforms the aerobic only group, but statistically speaking, they are not significantly different from one another," Willis says. So for double the time commitment, the additional benefit is not really worth it.

“This study should begin a discussion about guidelines for physical activity, ” says Willis. According to current guidelines, a combination of aerobic exercise and resistance training is the best way to lose weight and body fat, but “we just do not think that the data supports that.”

Willis and her colleagues are currently doing a study that takes the resistance training component out of the current study and compares the benefits of more moderate versus more vigorous intensity aerobic exercise.

“In general, I think the questions need to be cleared up on the benefits of resistance training,” Willis says. When you look closely at the scientific literature, resistance training has rarely been compared to aerobic exercise. “It seems intuitive that we would have already done this, but when you look at the literature, it has not been done very often.”

The study was published online in the Journal of Applied Physiology.