If you’re the kind of exerciser who constantly checks your heart rate to ensure you’re in the fat-burning zone, you should stop. You’ll probably never meet your weight-loss goals that way. That’s because there’s no special fat-burning zone that’s key to getting lean. Here’s what you need to know about the myth and about the true relationship between exercise and weight loss.
Yes, we know. If you look at the wall charts or cardio equipment in a gym, or listen to many personal trainers, you’ll be indoctrinated about the “fat-burning zone.” The standard advice for getting in this zone is to workout at about 60 percent of your maximum heart rate. That level of exertion is relatively low intensity; most people can talk in complete sentences while exercising at it. Working in this zone, it’s said, will burn more fat and result in greater long-term weight loss, compared with doing the same exercise at higher intensities.
There’s substance to part of this claim. Your body primarily fuels itself by burning a mix of stored fat and carbohydrates. The less active you are at a given moment, the greater the percentage of that fuel mix comes from fat. As your intensity of activity increases, the percentage of carbohydrates in that fuel mix also increases. At rest, fat constitutes as much as 85 percent of calories burned. That figure shifts to about 70 percent at an easy walking pace. If you transition to a moderate-effort run, the mix becomes about 50 percent fat and 50 percent carbohydrates, and it moves increasingly toward carbohydrates the faster you go.
So it’s true that at some workout intensities, you’re burning a higher percentage of fat than at other intensities. But that doesn’t mean this biological process is the key to losing weight from exercise. Experts explain that those who believe in a lard-melting zone simply aren’t seeing the forest — i.e., what it really takes to lose weight — for the fat-burning trees. They’re forgetting about calories.
