New research suggests that weight training may be more effective at controlling stubborn belly fat than aerobic exercise.

Researchers from Harvard University found that people who did twenty minutes of daily weight training had less of an increase in age-related abdominal fat compared with those who spent the same amount of time doing aerobic activities.

Combining weight training and aerobic activity led to the most optimal results. Aerobic exercise by itself was associated with less weight gain compared with weight training.

"Because aging is associated with sarcopenia, the loss of skeletal muscle mass, relying on body weight alone is insufficient for the study of healthy aging," Rania Mekary, lead author of the study and a researcher in Harvard School of Public Health's Department of Nutrition, said in a statement. "Measuring waist circumference is a better indicator of healthy body composition among older adults. Engaging in resistance training or, ideally, combining it with aerobic exercise could help older adults lessen abdominal fat while increasing or preserving muscle mass."

For the study, Mekary and colleagues examined the physical activity, waist circumference (in centimeters (cm)), and body weight of 10,500 healthy men aged 40 and older participating in the Health Professionals Follow-up Study between 1996 and 2008.

Their analysis included a comparison of changes in participants' activity levels over the 12-year period to see which activities had the most effect on the men's waistlines. Those who increased the amount of time spent in weight training by 20 minutes a day had less gain in their waistline (-0.67 cm) compared with men who similarly increased the amount of time they spent on moderate-to-vigorous aerobic exercise (-0.33 cm), and yard work or stair climbing (-0.16 cm). Those who increased their sedentary behaviors, such as TV watching, had a larger gain in their waistline.

"This study underscores the importance of weight training in reducing abdominal obesity, especially among the elderly," said Frank Hu, senior author of the study. "To maintain a healthy weight and waistline, it is critical to incorporate weight training with aerobic exercise.

Prior studies had been focused on a specific population (e.g. overweight or with type 2 diabetes) and were of short duration and had mixed results. The new study was long-term with a large sample of healthy men with a wide range of body mass index.

The findings are detailed in the online journal Obesity.