Fasted Cardio… A simple way to burn more fat with less effort and in less time right? Sounds too good to be true? Well, we’ll just have to see about that won’t we?!

First of all, let’s examine the word “fast”. In case you didn’t know, to fast means to not eat for a period of time.  For most people they only time they are fasting is when they are sleeping while others prefer methods like Intermittent Fasting which is simply to extend this fasting window by several hours. This means that they have a smaller window of time to consume all their calories for the day.

But whatever the case may be for you, the first meal after a fast is still called breakfast.  Get it?  “BREAK-FAST”? So whenever I refer to breakfast, that doesn’t necessarily mean the meal you have early in the morning.  It’s just the first meal of the day that breaks your fast.

What Is Fasted Cardio?

Now, there’s this theory that seems to go in and out of the spotlight in the fitness community that cardio on an empty stomach, or fasted cardio, produces more fat burning results.  This leads to loads of people literally rolling out of bed and going straight for a cardio session first thing in the morning.

But these people aren’t cranking out 6 minute miles.  Typically, we’re talking about low-intensity cardio because that’s likely the only thing you’ll be able to do without eating anything.  For most people high intensity interval training, for example, is out of the question, because you just won’t have the energy to do it and you might even feel extremely dizzy during or after.

The Theory Behind Fasted Cardio

So, the main question here is are these early bird runners wasting their time or boosting their fat burning potential?  Well, the actual theory behind fasted cardio is sound and it comes down to this:

  • A prolonged absence of food brings about a reduction in circulating blood sugar, causing glycogen (or stored carbohydrates) levels to fall. That leaves your body no choice but to rely more on fat, rather than glucose, to fuel workouts, especially those that last 45 – 60 minutes.
  • Also, the low insulin levels associated with fasting are conducive to fat breakdown, increasing the availability of fatty acids to be used as energy during the exercise session.

In simple terms, this means that when you perform your cardio on an empty stomach your body favors burning fat instead of carbs because your carb deposits are already low and your body prefers to hold onto them as much as possible in case a life-threatening situation arises and you absolutely require the immediate burst of energy. Makes sense, right?

In addition to this, if you perform fasted cardio often enough you’ll actually TRAIN your body to eventually favor burning fat rather than carbs which is a good thing if you want to get lean and right about now I bet this sounds great, right?

Will Fasted Cardio Burn Muscle?

But the next question you all should be asking is, what about burning muscle?  Research has indeed shown that while you fast, your body breaks down amino acids into glucose. So fasted morning cardio can potentially mobilize more amino acids (which are the building blocks of muscles) for fuel in addition to more fat, which isn’t ideal if building muscle is your primary goal.

To combat this a lot of people who fast drink BCAA’s,  while fasting and/or performing fasted cardio or they consume a fast digesting whey protein immediately after their workout to help lessen or eliminate muscle wasting.

How Your Metabolism ACTUALLY Works

Unfortunately though, fasted cardio will not produce better fat burning results for you, and that’s for a variety of reasons.

Reason No.1

While a lot of studies have indeed shown that you burn up to 20% more FAT calories while training fasted. Your body though, is more complicated than that and it continually adjusts its use of fat and carbohydrate for fuel depending on a variety of factors.

As a general rule, if you burn more carbohydrate while exercising, you’ll ultimately burn more fat in the post-workout period and vice versa.

So who cares if you burn a few extra fat calories while exercising fasted if an hour later the ratio shifts to a greater carbohydrate utilization? At the end of the day, it doesn’t make a bit of difference and you’ll have burned the same overall calories. You need to evaluate fat burning over the course of days, not an hour to hour basis, to gain a meaningful perspective on its impact on your body composition!

Reason No.2

It comes down to simple thermodynamics guys! You’ll eventually lose fat and become leaner if you shift your energy balance in a way that expenditure exceeds intake. That simply means, eat less food than your body actually needs and you’ll lose weight.  This is where the term caloric deficit comes from.

For example, let’s say you did 30 minutes of fasted cardio and you burned 400 calories and 300 of those calories were from fat (very optimistically). Now, let’s say you did 30 minutes of cardio but had a meal just before the cardio session. This time, you also burned 400 calories but only 100 of those calories were from fat and the rest were from carbs.

Well, when we look at this from a calories in vs calories out for the day comparison, there’s no difference.  In both cases, you still burned 400 calories which is all that matters. Calories in versus calories out. Period.

In a specific study I read, and I’m gonna link all these studies down in the info section below, they found out that what the participants benefitted from the most was the presence of supervised dietary restriction and mandatory exercise rather than the timing of their cardio sessions.

Reason No.3

The afterburn effect. Yes, it is a real thing. We all know that intense exercise doesn’t just burn a lot of calories while doing it, but your elevated heart rate and blood flow will continue to help boost your metabolism for several hours after and that’s because of EPOC and it stands for Excess Post-Exercise Oxygen Consumption. The afterburn represents the number of calories expended AFTER training and guess what? Eating BEFORE exercise promotes substantial increases in the afterburn effect! And want to guess where the vast-majority of calories expended in the post-exercise period come from? You got it, fat!

So at this point, killing yourself to do fasted cardio probably makes even less sense. At best, the effects on body composition won’t be any better than if you trained in a fed state; at worst, you’ll lose muscle and reduce total fat loss. Therefore, why even risk it?

HIIT Vs Low Intensity Fasted Cardio

Now with all that in mind, I personally suggest HIIT (High Intensity Interval Training) as the preferred method to burn max calories and of course on an empty stomach. HIIT is just alternating between moderate intensity intervals and high intensity intervals. So that can be jogging for a 1 minute and then sprinting for another minute. Repeat that for 10 times and you have a decent 20-minute max caloric burning cardio session. In comparison to low-intensity fasted cardio, you’re not only going to burn more calories while doing it, it will take you MUCH less time and you will be utilizing the afterburn effect to continue to burn more calories throughout the day.

Some other examples of HIIT can be:

  • 1 minute Walk/jog – 30 second sprint
  • 30 second walk/jog – 30 second sprint
  • 30 second walk/jog – 1 minute sprint

Basically, as you guys get stronger and increase your endurance, push yourselves during that 15 – 20 minute HIIT cardio session and play with the times to best suit the level of intensity you can handle.


Remember guys… in fitness there are no shortcuts and there are no magical supplements and there is no secret way to burn fat. It all comes down to hard work, exercising intensely and having a solid meal plan that you follow every single day. Trust me, hard work ALWAYS pays off, so don’t try to find ways to avoid it. What’s important is that you actually DO your cardio and if you can only do it, first thing in the morning when you wake up, that’s perfectly fine!

Knowledge is power guys and I want to make sure you are all ALWAYS making those gains!!!  If you have any questions or if you have any suggestions about future articles you want to see, be sure to leave them down in the comment section below!