The Myth Of The Fat Burning Zone

Ah... the “fat burning zone” - this is a prime example of exercise science and how it can change rapidly. But don’t worry, I’ll keep up with the latest in science for you and keep you updated.

This however, isn’t new news. The “fat burning zone” myth just keeps on lingering like a bad smell.

Old school fitness professionals constantly promote workouts in the “fat burning zone” as an effective way to burn fat. You might also see it on most cardio machines. See image below for exhibit A.  

Picture source


Sorry, I got ahead of myself - some people might not even know what the fat burning zone is and as much I would like to keep you naive to it, just in case someone tries to tell you about its “importance”, I must first tell you what it is.

What is the fat burning zone?

The FBZ (fat burning zone) comes from the idea that if you keep your heart rate in the “fat burning zone,” which is roughly 55% to 65% of your max heart rate, throughout your workout you will burn more fat. This is because at 50% of your max heart rate, your body burns a ratio of 60% fat to 40% carbs. At 75% of your max heart rate, the ratio is 35% to 65%, and at even higher intensities, the ratio is even lower. 

SIDE NOTE: To work out your max heart rate, minus your age by 220. So if you’re 37 years old your max heart rate is 183 beats per minute. So your “fat burning zone” would be 91-109 beats per minute.

I can hear you saying… “But Kristy I’m confused, doesn't that mean lower intensity steady state burns more of my fat so I should focus on keeping my heart rate there?”. Well, no... because the fat burning zone is misinterpreted. 

Why is it misinterpreted? 

Ok I admit, it exists, but it’s not the gold standard way to burn more fat. The reason why is because it’s all about calorie burn NOT fat burn. You burn a lot more calories when you workout at higher intensities than you do when you work out at lower intensity if you compare calories burnt each minute.

Confused yet? Let me give you an example. 

Our 37 year old woman from the example above who weighs 65kg only has 30 minutes to exercise. She thinks about the fat burning zone and goes for a 30 minutes walk ensuring her heart rate is at 91-109 beats per minute. She burnt 163 calories in her session.

If she were to do something like higher intensity circuit training (mixture of cardio and weights), not only will she burn 260 calories in that 30 minutes she will promote muscle growth which helps with your metabolism, bone health, and weight loss!

What about the carb to fat burning ratio.

Total calories burned is what matters, NOT what energy source the exercise burns. If you're exercising at this lower intensity, you're burning fewer calories per minute, which means less of a calorie deficit for the day, which means less weight loss over time. Fat loss comes down to being in a calorie deficit - no matter how you do it (eat less or move more), it's all about caloric expenditure. You must burn off more calories than you consume to lose body fat, simples. I don’t know about you, but if I only had 30 minutes to exercise I would rather work a little harder and burn more calories than work at a lower intensity and not burn as much.

DISCLAIMER: Before you go crazy with the intensity and burn yourself out, there is a time and place for high intensity training sessions and low intensity training sessions. I am NOT suggested low intensity exercise is a waste of time; all movement is good movement! A gentle jog, walk, or easy spin is a great way to clear your head, get re-energised, improve your health, spend time with friends and family, and, guess what else? Burn some calories!

My main message here is to not obsess about having your heart rate in these zones in the hope of burning more fat, and to mix it up! Variety is the spice of life! Have some harder, high-intensity days, followed by easier, low-intensity days and even some active recovery days like a gentle swim or playing with the kids in the backyard.

One last hot tip!

Aim to change up the durations of your sessions. When you have the time, do longer workouts at a comfortable lower intensity level of effort. When you're pressed for time, work a little harder and get that heart pumping.

Hope this helps bust the fat burning myth!

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