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You only start burning fat after 20 minutes: fact or fiction?

You often hear that your body only starts burning fat after 20 minutes of training. For that, only carbohydrates are consumed and your training does not really help you lose weight. A rather depressing thought, because then you are on that treadmill for nothing for the first few minutes.

But is it true that burning fat is only possible after 20 minutes? We explain where this theory comes from and take a good look at how much value it has for your training.

20 minutes of carbohydrates

What is the origin of the story that you only lose fat after 20 minutes of training? That has to do with your glycogen stores. Glycogen is glucose that is stored in your muscles along with a lot of fluid. With vigorous efforts, this is released to serve as a fast source of energy.

That glycogen stock is - depending on how much you have eaten - not unlimited. Measurements show that an average athlete is through it after about 20 minutes. And then, the theory goes, your body only starts to store fat as an energy source. So if you want to lose fat, this is a useful part of your training.

burning fat 20 minutes

Misunderstanding: you only use one energy source at a time

That all sounds quite logical at first glance. However, there are a number of misunderstandings behind this theory! The first of these is that your body would only use one source of energy at a time. It is either fats or carbohydrates, and only when the carbohydrates are used up do you switch to the fats.

Fortunately, your body doesn't work that simply. It can use several energy sources at the same time, depending on the effort. Even when you are using up glycogen, the fat burning can continue perfectly!

Misconception: Calories from carbohydrates 'don't count

Another misconception is that only energy consumption from fat would help to lose weight. That is not the case either. Yes, of course, you ultimately want to get rid of those lobules of fat. But it is not the case that you only make progress with this in the 'fat-burning phase'.

Calories that you burn from glucose also simply count. Well, it's not fat, but they are carbohydrates that you can no longer store as fat. All in all, you can simply add them to your total calories burned. And if that is lower than the number of calories you eat, then you will lose weight.

Misunderstanding: you only burn fat when you exercise

We can explain how this is possible on the basis of this last misunderstanding. Many people think that you are only burning excess fat while you exercise. In other words, you have to go through those twenty minutes of carbohydrates, because otherwise, you will never get rid of that fat!

Fortunately, that is nonsense. You burn fat from your fat reserves all day long – even if you sit quietly. After all, your body needs to stay warm and perform other maintenance tasks.

It is true that carbohydrate burning increases when you exercise. Normally, your body can manage just fine with fat, the less efficient source of energy. If you suddenly need a lot of energy, those fast sugars suddenly become useful as a supplement. However, that does not mean that you suddenly only use glucose. It just gets relatively slightly more.

Only burn fat after 20 minutes?

In short: how much is it true of the claim that you can only burn fat after 20 minutes? Not so much. Relatively speaking, you use more carbohydrates in those 20 minutes than at rest. However, because your total energy consumption is also a lot higher, a reasonable amount of fat is still being burned.

In addition, it is not true that burning carbohydrates does not help you lose weight. You cannot use the glucose that you have burned during exercise for something else. For that other task, more fat has to be burned. And so those first 20 minutes also have an effect in the end!

So a short training also works?

Some people are afraid to start HIIT training because of the 20-minute myth. After all, they are then 'not busy long enough to burn fat. Fortunately, the opposite is true: interval training is a good boost for your fat burning.

That's because such an intensive workout speeds up your metabolism for hours. So you get extra energy from your fat stores long after your training! And that means that on balance you sometimes lose even more fat than with a long, moderately intensive cardio workout.

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