by Alexander Perkins
There’s a myth surrounding the “fat burning zone” that suggests training at a lower intensity uses more body fat for fuel (higher fat oxidation rate) and is therefore better for fat loss. In truth, believing this and applying it to your training, could well be making you fat.
“Making you fat” may be a stretch if you’re still hitting the weights and eating well, but if not, you could be burning far less energy in the gym as you otherwise would be. Thus ensuring much of that time is near enough to wasted, and your fat loss goals further away than ever.
Here's what you need to know about the fat burning zone, why training in it can be a waste of time, and what you need to be doing instead.
What is the Fat Burning Zone?
The theory for the “fat burning zone” isn’t cooked up out of nothing. It’s due to the fact that when you’re exercising at an intensity that brings your heart rate up to around 60% of its maximum, your body oxidises more fat for fuel.
As you increase intensity and your heart rate starts to climb, you begin to use more stored carbohydrate for fuel. That’s because carbohydrate releases energy faster than fat, hence why it can be such a limiting factor when it comes to performance; especially in sports that require a mixture of explosive power, speed, and endurance.
Note that it’s never a case of either or. Whatever activity you’re doing, your body will be using both carbohydrate and fat for fuel, as well as creatine and protein at varying rates depending on the intensity and duration.
The “fat burning zone” is the colloquial name giving to this former heart rate zone where your body uses more fat as a primary fuel source; which is usually anywhere between 50-70% of your maximal heart rate.
So in theory, it makes sense to train at a lower heart zone if you want to burn body fat right?
If you’ve spent any time in a gym over the past few decades you won’t be scolded for believing this to be true. Images like the ones below are often plastered all over cardio equipment in commercial gyms.
To the uninformed, they offer some direction around how to use equipment to achieve a desired goal. The problem is, it’s the wrong direction.
At best this message is responsible for countless hours wasted. At worst, it’s the reason so many people give up on their goals after that wasted time and effort saps them of motivation and instils a feeling of helplessness.
The following is why it doesn’t work and why you’ve got to up the intensity to burn body fat.
Why the Fat Burning Zone is a Waste of Time – And the Better Training Approach for Fat Loss
Fat oxidation does not equal fat loss. That is to say that burning more fat as fuel during your gym or cardio sessions, doesn’t necessarily mean you’re going to burn more body fat over time.
Like anything in exercise or nutritional science, the data have to be contextualised. In this case, what’s best for oxidising fat over a 45 minute training session is rarely going to be best for fat oxidisation over a 24 or 48 hour period; or better yet, over weeks or months of training.
Opting for doing the most work, over a long period of time – alongside eating a diet specific to your goals – is going to be best for fat loss.
Looking at the micro level of one training session, that’s usually going to mean doing a higher intensity workout.
Sure, you’re going to oxidise less fat during that workout, and increase the use of stored carbohydrate, but what about fat oxidation post-exercise? We know that higher intensity exercise induces a higher metabolic rate once a session is complete; a phenomenon known as Excess Post-Exercise Oxygen Consumption (EPOC).
Perhaps more importantly, a higher intensity session elicits a higher total calorie expenditure during that session. It’s fairly well established that a calorie deficit is the foremost principle of any fat loss plan. So it’s a small stretch – and one most exercise and nutritional scientists are willing to take – to suggest that doing more work and burning more energy in a session is of more importance to fat loss than using fat as a primary fuel source.
To contextualise this even further, that work has to be spread out across a long period of time. That is to say that fat loss comes from not just dominating one high intensity workout, but by maximising your ability to do as many of those workouts over months and months.
In practise, this usually looks like a combination of resistance training, higher intensity cardiovascular exercise, lower intensity sessions, recovery sessions, and even complete days off.
Whilst for an athlete this may be planned out meticulously, for the everyday gym goer, a few days a week spent lifting weights alternating with some higher intensity cardio sessions would do the job.
Do this and ensure your diet is meeting your protein needs (which increase when dieting, so supplementation can help here), whilst remaining in a calorie deficit (eating less than what you need), apply it consistently over a long period of time, and you’ve got a recipe to burn body fat whilst maintaining muscle and increasing your fitness at the same time.
That’s going to be far more beneficial than spending wasted time walking or cycling at a pace that’s of little benefit to either burning a stack of calories or increasing your fitness. In the words of Jim Wendler, “if you’re going to be walking for your cardio, you better be carrying something”.