The Myth of the Fat-Burning Zone

I rarely use cardio machines at a gym but, when I do, I find it half-amusing and half-irritating when I see a “fat-burning” program listed.  I wonder how many people select those programs assuming that, when they’ve finished their workout, they’ve burned off more body fat than if they had spent the same amount of time on the machine using a different program.  That assumption would be incorrect.  Yet, the suggestion by the cardio machine manufacturers that there is a particular intensity of exercise that relies mostly on fat for energy isn’t entirely a lie either.

To explain, we need a little Cardio 101.  There are 2 sources of stored energy available for the body to burn (in the form of calories) during exercise: carbohydrates and fats.  Think of carbohydrates as being like kindling in a fire (quick burning) and fats being like a large log on a fire (slow burning).  At every exercise intensity, a combination of both are used for energy.  At most intensities, a higher percentage of carbs is used than fats.  However, there is a narrow state of cardio exercise at which the percentage of fat burned is higher than the percentage of carbs burned – this is what is known as the fat-burning zone.  For the average person, the fat-burning zone would be a brisk walking pace, a pace just below jogging.  However, the machine has no idea if an “average” person is on it.  If the person on the treadmill is an avid runner, the pace in the fat-burning program will likely be too slow to be in the fat-burning zone for that individual.  The opposite is true if the person is extremely deconditioned.  But all of this is really moot because fat calories are being burned at every level of exercise, not just in the fat-burning zone.  If you can burn a high amount of total calories, you will also be burning a high amount of total fat calories.  So, for those who are interested in exercising for weight loss, total calories burned during a workout is really the only number that’s important.

Why?  The general rule of thumb for an overweight person is she needs to have a caloric deficit of 500-1000 calories per day to lose 1-2 lbs per week.  Furthermore, it is understood that the healthiest way to achieve that caloric deficit is through a combination of reduction in calories consumed and an increase in calories expended via exercise.  Therefore, the goal should be to burn the most amount of calories possible in a given workout rather than be concerned about what type of calories are being burned.

Let’s say that Jane is about 10 pounds overweight and she’s decided to use a treadmill for 30 minutes 3 times a week in order to lose the weight.  If Jane doesn’t know any better, she would be tempted to select the fat-burning program believing that she will burn more of her 10 pounds of excess body fat in 30 minutes than if she selected a different program.  But the truth is, she can burn twice as many calories (and more total fat calories) jogging at 6mph than walking at 4mph for the 30 minutes she spends on the treadmill.

But, understandably, Jane, a novice exerciser, isn’t yet physically or mentally ready to jog instead of walk for 30 minutes on a treadmill.  The better alternative for Jane is to do intervals on the treadmill.  Numerous exercise studies have proven that interval training burns more calories than an equivalent time of steady-state training.  At first, Jane may be able to walk at a 3mph pace for 4 minutes and at a 4mph pace for 1 minute.  In 30 minutes, she can perform 6 bouts of these intervals.  Over time, she can work on shortening her slower pace interval and lengthening her higher pace interval.  Eventually, she may be able to bring her high interval pace up to a jog.  In other words, she’ll be able to increase her caloric expenditure per workout over time without needing to increase her 30 minute workout period.  This is so important in weight loss because, without it, Jane is more likely to reach a weight-loss plateau before she meets her goal.

It’s just like your mom said: If something seems too good to be true, it probably is.  Wouldn’t it be great if we could melt off body fat by choosing to go for a leisurely walk over a grueling run?  If only!  But now you’re armed with knowledge.  Next time you hop on a cardio machine, you’ll know to select the interval program and snicker at that so-called fat-burning program.

Author’s Note: Always consult your physician before beginning any new exercise program.

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2 comments

  1. […] #2: Low-Intensity Exercise Burns More Fat than High Intensity Exercise  My previous post on The Myth of the Fat-Burning Zone explains this ins and outs of fat burning.  Bottom line: If one of your exercise goals is weight […]

  2. Reblogged this on fitandhappier and commented:

    This was one of my most popular posts and also happened to be among my first few. I thought my new readers would appreciate the low-down on this myth debunked and my faithful readers wouldn’t mind the refresher.

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