Interestingly, this myth has some truth to it. The ‘fat burning zone’ is indeed, a real thing.
If you have a FitBit, or Apple Watch, or any type of smart watch for that matter, you may have seen it flash up on the screen at some point in time.
“Congratulations, you have spent X amount of time today in the ‘fat burning zone’!”
You could easily be forgiven for thinking to yourself “GREAT!…that’s exactly where I need to be.. right?!”
Unfortunately, not really.
99% of people don’t actually want to be training in this zone…
Let me explain why:
We’re going to take two 30 minute workouts, and compare the pair.
Typically, this is what the fat burning zone may look like
Workout A is done at low intensity (around 50-65% of your relative heart rate max), while Workout B is done at a higher intensity (around 75-85% of your heart rate max).
Workout A burns 200 calories. Of those calories, approximately 60% have come as a result of utilising fat as the body’s fuel source.
Hence, the ‘fat burning zone’.
There’s just one problem…
Workout B burns 400 CALORIES. Double the amount. In the same length of time.
Here is what the fat burning zone does NOT look like
The only difference is that due to working at a higher intensity, the body had to utilise another fuel source, called glycogen. Glycogen resides in the muscles, and can be easily thought of as the stored version of carbohydrates.
Of those 400 calories, approximately 65% came from using muscle glycogen, while only 35% were from using fat.
So yes, in Workout A, a greater percentage of the calories burnt came from fat than Workout B.
But overall, Workout B burnt double the amount of calories.
Now, as we know, to lose weight, we want to expend more calories than we intake.
So for most people hoping to lose weight, working out and burning 400 calories is far, far preferable than burning only 200 calories, right?
If you had a choice, and had only 30 minutes, to lose weight you would do Workout B over Workout A and the ‘fat burning zone’ every day of the week.
SUMMARY; The fat burning zone is a thing. It is just not where you want to spend your time.