“Hey, let’s skip the pancakes this morning and go jogging instead.”
– No one ever
I mean… Cardio is pretty tough as it is, and now people want us to do it without eating our morning pancakes first? #psychos
Here’s what we’ll cover in this article:
Table of Contents
What is Fasted Cardio?
Fasted cardio is the painful art of doing any cardiovascular activity when your body is no longer processing food, which typically happens 4 to 6 hours after your last meal.
Since it’s easier to fast overnight, many people prefer to do fasted cardio in the morning before having breakfast.
Why Do People Believe Fasted Cardio is Better for Fat Loss?
This belief comes from the idea that when you are in a fasted state, the low levels of glycogen and insulin will make the body switch from using carbs as energy to using mostly body fat.
Glycogen is the stored form of carbs.
Since you’re not eating at night, your body will use the glycogen stores for energy, this is why you’re most likely to have low glycogen levels when you wake up.
If you then go and do cardio, the body will have no choice but to use mostly body fat for energy.
High levels of insulin prevent the breakdown of fats (lipolysis). Therefore, doing cardio when insulin is low should allow you to breakdown fats and use them as energy during cardio.
The Research Behind It
A number of studies have shown that doing cardio while fasted burns more fat during the session than doing it in a fed state.
Study (1) showed that those doing fasted cardio burned 20% more fat during the session than those who were on a fed state.
Study (2) showed that eating carbs during the cardio session will make the body use more carbs than fat for fuel.
Study (3) showed that a group of men who cycled for 60 minutes in a fasted state had better fat oxidation and lipolysis than the fed group.
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Fat Burning Does Not Mean Fat Loss
While it is true that you burn more fat during the cardio session itself if you’re in a fasted state, burning fat and losing fat are not the same thing.
Just because you burn more fat during the cardio session doesn’t mean that you will lose more fat overall.
If you burn more fat during the cardio session, you will burn less fat for the rest of the day. Likewise, if you burn more carbs during cardio, you will burn fewer carbs for the rest of the day.
Explore More: Fat Loss vs. Weight Loss – What’s the Difference?
The Research Behind It
Study (4) showed that doing fasted cardio didn’t increase total fat burned in a 24-hour period.
A systematic review (5) found that there was no difference in overall fat loss between the group that did fasted cardio vs. fed cardio.
A study (6) showed that as long as you are in a caloric deficit, doing cardio in a fasted or fed state has no impact on body composition.
This other systematic review (7) found that fasted compared to fed exercise does not increase the amount of weight loss and fat mass loss.
In the end, fat loss depends more on a person maintaining a caloric deficit than it does from doing cardio in a fasted or fed state.
You May Burn More Calories if You Eat Before Cardio
A study (8) showed that those who ate before training had a better VO2 max than those who didn’t.
VO2 max is the measurement of the maximum amount of oxygen a person can use during intense exercise.
The more oxygen a person consumes during intense exercise, the more ATP (energy) the body generates.
This is likely because having something to eat before training will help you perform better and push harder during the session than if you were fasted.
Explore More: To Increase Cardio or Lower Calories?
Should You Do Fasted Cardio?
Since the amount of fat you burn is mostly dependent on you being in a significant caloric deficit for an extended period rather than performing cardio in a fasted or fed state, it’s safe to say that choosing between fasted cardio or fed cardio comes down to personal preference.
Depending on how many cardio sessions I have scheduled for the week, I sometimes like doing a few of them fasted, this way I don’t have to think about it during the day.
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