Good news if you are trying to walk off weight. Researchers at Duke University found that aerobic exercise, such as brisk walking, was better at burning off belly fat and liver fat than resistance training. The test subjects were 196 overweight, sedentary people. Over four months, not only did they lose belly fat (visceral fat), but they reduced other risk factors of heart disease and diabetes, including fasting insulin levels and fasting triglycerides. Unfortunately, those who just did resistance training routines had no improvement in belly fat or the other measures.
What they did: The aerobic exercise group jogged for 12 miles per week at 80% of their maximum heart rate (heart rate calculator). That is a vigorous intensity that isn't normally achievable by walking. However, the lead researcher, Duke exercise physiologist Cris Slentz, Ph.D., says that he believes moderate intensity exercise such as brisk walking at 50-70% of your maximum heart rate can produce similar results.
Walking Works to Burn Belly Fat
Lead research Dr. Slentz explained, "In a previous study we showed that moderate intensity walking was equal to vigorous exercise when the total calories expended per week were equal. That is why we prefer to describe our exercise prescription in terms of miles per week of activity. That way when someone who is not very fit walks or jogs, they know how far they need to go. When they expended the same number of calories (as those who were jogging), they had the same changes in visceral fat and subcutaneous abdominal fat. But the moderate intensity group exercised on average about 3 hours per week and the vigorous group exercise right at 2 hours per week."
Walking in the Fat-Burning Zone
"In fact when you exercise at a moderate intensity you actually have a greater amount of fat burning then you do when you exercise at vigorous intensity, if you are, say, covering a mile or a certain distance. The total calories burned is fairly similar when you walk or jog a mile (not identical though.) Walking you might get something like 50-60% of your calories from burning fat versus maybe 30-40% of your calories if you covered the same distance by jogging (the amount of fat burned depends on your fitness partially). In fact, some research suggest that most untrained folks burn the maximal amount of fat at 50% of vo2 peak," says Slentz.
Walking Calorie Calculator
It's the Total Miles and Total Calories that Count
"It is very important that we are discussing the same amount of work or same distance. If you go out and jog for 30 minutes versus walking for 30 minutes the answer is that you burn more fat jogging... simply because you burn way more calories all together. For example, if I am pretty fit and I jog at an 8 mile per hour pace, I will cover 4 miles in 30 minutes. If instead I walk very briskly at 15 minute per mile, I will only go 2 miles and therefore burn only half as many calories at best. Therefore less total fat and less total carbohydrate is used for energy," explained Slentz.
Walking Calorie Calculator
Meanwhile, in the Duke study, the resistance training group that was working out three times per week with three sets of 8-12 repetitions. They did not see any results reduced visceral fat. A third group did both the running and the resistance training. Their results were the same as the running group, with no additional benefits.
"I absolutely believe that it mainly about total calories burned and we and others have shown that resistance training (the way it is traditionally done) burns far fewer calories... maybe 50% for men and maybe even less for women (cause they have less lean body mass and less ability to lift a lot of weight)," says Slentz.
Does this mean you can shun the weight machines and put away the resistance bands? No! Resistance exercise is still recommended to improve or maintain strength and lean body mass. But just don't expect resistance training alone to help you lose unwanted belly fat.
Strength Training Basics
Source: Slentz CA, Bateman LA, et.al. "The Effects of Aerobic versus Resistance Training on Visceral and Liver Fat Stores, Liver Enzymes and HOMA from STRRIDE AT/RT: A Randomized Trial." Am J Physiol Endocrinol Metab. 2011 Aug 16. [Epub ahead of print]
Interview with Cris Slentz, Ph.D. 8/30/11
Photo © Wendy Bumgardner