It’s cold outside. And as the temperature dips, many New Yorkers head indoors to work out, trading the soupy city streets for a treadmill or stationary bike. And that’s where many of us encounter a puzzling (and often dated-looking) diagram pointing out the so-called “fat-burning zone.”
The reason it’s plastered all over the gym? Proponents of the zone argue that it represents a kind of exercise sweet spot—typically between 60 and 70 percent of our maximum heart rate—in which our bodies burn the most fat.
So should we buy into the idea?
In a word—no.
On average, when we’re resting, 60 percent of the energy we use for fuel comes from fat, 35 percent comes from carbohydrates, and the remaining five percent comes from protein. But when we exercise, our bodies begin burning more carbohydrates to fuel our activity, and less fat. All of which has led some to argue that we should work out at lower intensities to trick our bodies into using more fat as fuel.
Unfortunately, that’s not true.
“The practical way most people think about the fat-burning zone is that they’re using more fat to fuel their exercise and therefore, they’re going to lose more body fat,” says Dr. Karen Reznik Dolins, a professor of nutrition and physical education at Columbia University. “That’s incorrect. The amount of fat you’re going to lose is totally dependent on expending more calories than you take in.”
In other words, the problem is that as you decrease the intensity of your workout, you also decrease the overall number of calories you burn.
What matters most when it comes to exercise and weight loss is using as many calories as possible, so that at the end of the day, you’ve expended more than what you’ve consumed. According to Dr. Reznik Dolins, most people are likely to achieve this goal by exercising as strenuously as possible. (Hey, we don’t mind a few intervals.)
The bottom line? The idea that there’s some kind of magic zone whereby you exercise less intensely, don’t increase the length of your workout, and somehow burn more fat is, sadly, false. —Catherine Pearson
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