Physical activities like walking, hiking, running, and swimming are better than resistance training for burning fat, according to a new study. The study by researchers from Duke University in Durham, North Carolina, is the largest randomized trial that ever analyzed changes in our body composition from the three main ways that we get exercise.
These ways are (1) aerobic training -- the activities like walking, hiking, running, and swimming, (2) resistance training like weight lifting, and (3) a combination of these two. In the conventional wisdom people had believed that increased metabolism from resistance training alone could reduce our body mass or fat mass, but the study found that it didn’t.
The study, “Effects of aerobic and/or resistance training on body mass and fat mass in
overweight or obese adults,” appears in the December 15 issue of the Journal of Applied Physiology. Only the abstract of the study is online, but the lead author, Leslie H. Willis, kindly sent me the full-text. He is the clinical research coordinator at Duke Medical Center - Cardiology.
Willis and his associates enrolled 234 overweight or obese adults in the study. They were between 18 and 70, previously sedentary nonsmokers who didn’t have a history of diabetes, high blood pressure, or coronary artery disease. Since none of them had diabetes, we can’t be sure that the results of the study apply to us.
The researchers randomly assigned the people in the study to each of these three exercise groups: one-third got resistance training (weight lifting three days per week of three sets per day and 8 to 12 repetitions per set), aerobic exercise of about 12 miles per week, or a combination of these two. Then, the researchers analyzed the results of the 119 people who completed the study.
The people in the resistance training group actually gained weight. But that was because they increased their lean body mass. The people in the other two groups lost weight.
But the most interesting part of the study is that aerobic exercise alone is the most efficient type of exercise for us to lose body fat. People in this group spent on average 133 minutes a week in training, and they lost weight. The people in the resistance training group spent 180 minutes a week in their training, and gained weight.
The people in the combined training group exercised for about 323 minutes a week but didn’t get double benefit. They did lose weight and fat mass, but it wasn’t significantly more than from aerobic training alone. Those in the combined training group did reduce their waist circumference the most, probably because they spent a lot more time exercising.
“No one type of exercise will be best for every health benefit,” Willis says. For example, earlier research showed that resistance training improves strength, lean body mass, glucose tolerance, and A1C level. But aerobic exercise is best for weight loss.
“Balancing time commitments against health benefits, our study suggests that aerobic exercise is the best option for reducing fat mass and body mass,” says Cris A. Slentz, PhD, a Duke exercise physiologist and a co-author of the study. “It’s not that resistance training isn’t good for you -- it’s just not very good at burning fat.”