Health & Wellness

To blast belly fat, do this for 20 minutes a day, Harvard study says

For those battling belly fat, weight training may be a better option than aerobic exercises like jogging and running, a new study suggests.

The very best choice would be a combination of the two.

Men who did 20 minutes of daily weight training had less of an increase in age-related abdominal fat than those who spent an equal amount of time doing aerobic activities, Harvard researchers reported Monday online in the journal Obesity.

While men who did aerobic exercise lost more weight than those who lifted, their waistlines still continued to expand. That’s because weight lifting adds muscle mass — something we naturally lose as we age — while aerobic exercise contributes to a loss of fat along with muscle mass, says the study’s lead author, Rania Mekary, a researcher with the Harvard School of Public Health and an assistant professor at MCPHS University in Boston. 

“That’s why people who do marathons are very, very slim and don’t have a lot of muscle on them,” she adds. “As we get older we need an activity that helps us maintain muscle mass.”

Mekary and colleagues scrutinized the physical activity, waist circumference and body weight of 10,500 healthy American men, aged 40 and older, who had been participating in the Health Professionals Follow-up Study between 1996 and 2008. Men who increased the amount of time spent in weight training by 20 minutes a day had less gain in waistline measurements compared to those who increased moderate to vigorous aerobic exercise by a similar amount, they found.

Not surprisingly, those who increased the amount of time spent in sedentary behaviors, like watching TV, had the greatest increase in their waistlines.

Weight loss expert Kathryn Schmitz says a study she did last year suggests that the results would be similar in women. 

“We did a two-year intervention study in premenopausal women who did only twice weekly weight training,” says Schmitz, a professor at the Perelman School of Medicine of the University of Pennsylvania. “We didn’t ask them to do any aerobic activity or to make any dietary changes. We found that twice weekly weight training substantively prevented increases in belly fat in women who got the intervention versus those who did not.”

Jenna Wolfe's 10-minute circuit workout that tones abs and arms

Weight training gets better results than aerobic activity because you’re building “a bigger engine,” says Ron DeAngelo, director of Sports Performance Training at the University of Pittsburgh Medical Center.

“With weight training you’re going to gain lean body weight and that is going to make metabolism go up,” DeAngelo says. “So consequently your engine gets bigger and you burn more calories even when you are at rest.”

It’s like the difference between a fuel-efficient Honda and a gas-guzzling Hummer. The bigger engine just needs more fuel to run. While that may not be what you’re looking for in a vehicle, it can be an advantage for human beings.

The best case is if you combine high-intensity cardio workouts with weight lifting, DeAngelo says. “That’s better than going out for a long walk or jogging endless miles,” he adds.

The weight lifting can be done at the gym or in your own home with dumbbells, Mekary says. “Try to target two muscle groups per day,” she suggests.

Women might want to start with 5- or 10-pound dumbbells, Mekary says. Men can begin with heavier weights.

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Linda Carroll is a regular contributor to NBCNews.com and TODAY.com. She is co-author of "The Concussion Crisis: Anatomy of a Silent Epidemic” and the recently published “Duel for the Crown: Affirmed, Alydar, and Racing’s Greatest Rivalry.”


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