What’s The Deal With The Fat Burning Zone?

July 13, 2016

Picture if you will… Jane Doe, a devoted wife and mother of three, leaves the gym having just finished her daily exercise routine; she makes the Bataan death march on the treadmill every morning without fail. Despite her effort, this dutifully dedicated dame finds her results to be maddeningly lacking. She speeds on to the highway onramp, desperate for an answer. Anyone or anything to break her out of this rut…

The place is here, the time is now, and the journey into the shadows that we’re about to watch could be your journey. This highway leads to the shadowy tip of reality; you’re on a through route to the land of the different, the bizarre, the unexplainable…you’ve just crossed into The Fat Burning Zone.


Doesn’t it feel like that sometimes? What in the hell is the fat burning zone, anyway? That mystical setting on cardio equipment that tells you you’re burning fat when you’re barely breaking a sweat. It is the enigma that has puzzled many a gym goer over the years. No more, I say! Let’s demystify this phenomenon once and for all.

Does your body actually burn fat while training in the fat burning zone?

Yes. When you’re training in the fat burning zone, your pace is typically stagnant and your level of intensity is low. The body prioritizes different fuel sources depending on the intensity of the activity. At lower intensities, fat is the primary source of fuel. Hence, the concept of the fat burning zone. At higher intensities, carbohydrates become the primary source of fuel.

So, when I want to lose weight, I should stay in the fat burning zone because my body will burn more fat…right?

Wrong. One of the biggest fallacies of the fat burning zone is the idea that the body is going to burn more fat while training at this lower intensity. Just because the body uses fat as the primary fuel source during low intensity exercise, doesn’t necessarily mean that it will burn more fat than it would during high intensity exercise of the same duration. Consider this example:

Scenario 1: On Monday, Jane jumps on the treadmill for her daily cardio session and spends 30 minutes walking at 3.0 mph. She burns 150 calories (5 cals/min), 65% of which are fat (97.5 cals) and 35% of which are carbohydrates (52.5 cals).

Scenario 2: On Tuesday, Jane, feeling the need for speed, hits the ground running at 6.0 mph for the same 30 minute duration. She burns 300 calories (10 cals/min), 45% of which are fat (135 cals) and 55% of which are carbohydrates (165 cals).

The results don’t lie, folks. When Jane trained at a higher intensity, she burned 38% more calories from fat (37.5 cals) and twice the amount of total calories. So, she burned more fat and created a larger calorie deficit.

Does lower intensity exercise have any place in the average person’s fitness plan?

After being beaten like a red-headed stepchild, the fat burning zone pleads it’s case. Low intensity exercise definitely has its uses. Here are a few:

For those new to fitness and those with a condition. People who are de-conditioned, regardless of reason or age, may not be ready to jump straight into high intensity exercise. Those that are able, can use lower intensity exercise as a stepping stone while they build their stamina and cardiovascular capabilities. For some with heart conditions, high intensity exercise may not be an option at all. Longer bouts of lower intensity exercise can provide this group a way to burn fat and calories while not putting them at risk for a cardiac event.

For use as active rest. I love to train and I train nearly everyday. Because I crave physical activity as much as I do, I have a hard time convincing myself to take a day off. So, when I’ve been training hard and am feeling a little beat up, I like to engage myself in active rest. For me, this means walking, going on hikes and rucks, or slow-moderate paced biking. I get the opportunity to be active, while not overtraining. It’s a win/win.

Let’s be real, most people don’t have the time nor the desire to train everyday. Frankly, unless you’re training for a major event or you’re like me and can’t sit still, there’s no reason you should be. But, active rest can be of use to you, even if you’re not training as frequently. Let’s say you train 3 days a week at higher intensities and currently take the other 4 days off. Pick at least one of those 4 days off and insert active rest for an hour. Choose something that is of interest to you, something active, that keeps your heart rate at a low-moderate level for an extended period of time. It might be one of the outdoor activities that I mentioned above. Or, you might like to zone out on a bike or an elliptical machine with a good book or a podcast. Regardless, you get one more day of activity, doing something of your choice, and you’ll most likely find yourself energized and recharged.


Her name is Jane Doe, devoted wife and mother of three. Her search nearly drove her insane. It thrust her into the fifth dimension, into a dimension as vast as space and as timeless as infinity. She comes back to us now with the sobering conclusion that the answer to her quest for health and happiness lies both in… and out… of The Fat Burning Zone.