What Is the Fat Burning Zone?

Learn about the fat burning zone, how to burn fat fast, and how to use the fat burning zone in your workout.

Ben Greenfield
4-minute read
Episode #15

There is a deep, dark, mysterious exercise secret that personal trainers and fitness pioneers have struggled for decades to hunt down. Like Bigfoot, the Loch Ness Monster, and goose that laid the golden egg, the one who discovers this elusive secret will go down in infamy and live eternally glorified in exercise manuals everywhere. Folks, that’s how most people understand the fat-burning zone, but by the time you finish this article, you’ll know the best way to discover your personal fat-burning zone, and exactly how to use it.

How Does the Body Make Energy?

As you learned in “How to Tone and Lose Fat In One Body Part,” your body relies on fat as a primary fuel. But because the body is a complex machine, it is able to make energy from other fuel sources too--like protein and carbohydrates. Throughout the day, each person uses a combination of carbohydrate, fat, and protein fuel sources to create the energy necessary to sit up, climb stairs, filter blood in the kidneys, make the automatic lung muscles function, help the heart to beat, and even lift a fork to eat.

Fat: the Most Efficient Energy Source

The most efficient energy source is fat. One pound of stored fat can provide 3,600 calories of energy, which is far more than most people burn in a single day. In comparison, a pound of storage protein or carbohydrate provides less than half that much energy. Because fat provides so much energy, the body relies primarily on fat during rest and during relatively slow and easy physical activity. From an evolutionary survival standpoint, that makes sense, since most people can only store about 2,000 calories of carbohydrate on their entire body. If you burned carbohydrate as your primary fuel, you’d have to be finding food and eating all day long. Furthermore, if your burned protein as your primary fuel source, your body would have to break down muscle and other organs to get the protein fuel--or you’d have to be rooting around for nuts, seeds, eggs, and meat all day long.

How the Body Uses Carbohydrates

However, once you begin moving quickly, you suddenly present your body with a fuel paradox. Though fat is plentiful on your body (even a 150 pound individual with 5% body fat has 27,000 calories of stored fat energy!), and provides many calories for exercise energy, it simply doesn’t provide that energy as quickly as carbohydrates. When the body needs to get from point A to point B quickly, or needs to hoist a heavy object overhead, it needs immediate energy, and that’s where carbohydrates come in. They may not provide as much energy, but they certainly provide it far faster than fat.

So as you progress from a standstill, to a walk, to a jog, to an all-out sprint, your body begins to tap into carbohydrates more and more, while reducing its use of fat as a fuel. Of course, during this entire progression, you’re burning more overall calories too. So while the percentage of fat used as a fuel is decreasing, the total fat calories you burn might still be increasing.

What Is the Fat-Burning Zone?

For example, if you burn 200 calories per hour while walking, and burn 60% fat, then you burn 120 fat calories per hour. But if you burn 600 calories per hour while jogging, and only burn 40% fat during that time, you still burn 240 calories of fat per hour, twice as much as when you were walking. Using this concept, the point at which fat burning peaks during exercise is referred to as the peak “fat burning zone”.

How to Find Your Fat-Burning Zone

Research shows that both cardio intervals and resistance training help you lose weight faster than exercise in your peak fat-burning zone.

In most individuals, the fat-burning zone occurs at 45-65% of the maximum heart rate, and that is the typical calculation used by personal trainers. They’ll take the number 220, and subtract your age to find your maximum heart rate, then take 45-65% of that number to find your maximum fat-burning zone.

But this number is highly variable and tends to be erroneous, primarily because the maximum heart rate is highly variable. So here is your quick and dirty tip for finding your personalized fat-burning zone far more accurately:

  1. Warm up on a bike for 10 minutes.

  2. Pedal at your maximum sustainable pace for 20 minutes. You should be breathing hard and your legs should be burning, but you should be able to maintain the same intensity for the full 20 minutes.

  3. Record your average heart rate during those 20 minutes.

  4. Subtract 20 beats from that heart rate. Add and subtract 3 beats from the resulting number to get a range, and that is your peak fat burning zone.

For example, if your average heart rate was 160, 160-20 is 140, 140+3 is 143, 140-3 is 147, and so your peak fat burning zone is when you have a heart rate of 137-143 beats per minute.

[[AdMiddle]Compared to the results that I have obtained from hundreds of individuals in a professional exercise physiology lab with all sorts of gas masks and gadgets, this method obtains very similar results. But if you did want a laboratory test to find your personal fat-burning zone, then you would be looking for something called an Exercise Metabolic Rate test, also known as a VO2 Max Test.

Congratulations. You’ve now discovered the elusive fat-burning zone. But don’t go celebrate yet!

How to Exercise with the Fat-Burning Zone

As you learned earlier, the fat-burning zone doesn’t necessarily burn a high amount of calories. If you do all your exercise in the fat-burning zone, then you’ll never develop strong lungs, muscles, or much fitness and athleticism. Furthermore, research shows that both cardio intervals and resistance training help you lose weight faster than exercise in your peak fat-burning zone.

An ideal workout program mixes cardiovascular exercise in the peak fat-burning zone on easier, recovery days with a combination of resistance training and cardio intervals that go above the fat-burning zone on harder days. Here is a sample workout week that incorporates the fat-burning zone:

Day 1: Strength training (refer to this page for more strength training tips) – 40-60 minutes

Day 2: Peak fat-burning zone cardio – 40-60 minutes

Day 3: Cardio intervals (refer to this page for cardio interval tips) - 40-60 minutes

Day 4: Off

Day 5: Strength training (refer to this page for more strength training tips) – 40-60 minutes

Day 6: Peak fat-burning zone cardio – 40-60 minutes

Day 7: Cardio intervals (refer to this page for cardio interval tips) - 40-60 minutes

With the workout above, you give your body a chance to burn fat fast with the resistance training and cardio intervals, but you also get to utilize easier days to also burn fat, but without quite as much strain on the body. And compared to hunting down Bigfoot, this approach to exercise is far easier to implement and it gets much more satisfactory results.

All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Ben Greenfield

Ben Greenfield received bachelor’s and master’s degrees from University of Idaho in sports science and exercise physiology; personal training and strength and conditioning certifications from the National Strength and Conditioning Association (NSCA); a sports nutrition certification from the International Society of Sports Nutrition (ISSN), an advanced bicycle fitting certification from Serotta. He has over 11 years’ experience in coaching professional, collegiate, and recreational athletes from all sports, and as helped hundreds of clients achieve weight loss and fitness success.