Does Fasted Cardio Burn Muscle?

The bodybuilding world is always changing. There’s always some new technique or method coming up. One such method that has become quite popular among bodybuilders is the fasted cardio technique.

Fasted cardio is performed on an empty or fasted stomach. Being a new technique, still a lot is unknown about the technique. Yet, it has proven to be popular.

One of the more common questions about fasted cardio is if it burns muscle?

So, does fasted cardio burn muscle? Generally speaking, no. Fasted cardio does NOT burn muscle, it usually burns fat. The only time it will burn muscle is if you have low protein in your blood- a simple fix for this is eating a proper amount of protein the day before or taking BCAAs- it’s a small powder that puts amino acids in your body to stop this muscle loss process.

(It should be noted: HIIT cardio and weight training should generally be avoided when doing fasted cardio. Stick to moderate-low intensity cardio like jogging to get that true fat burn, and weight training will cause muscle loss. Save the weight training and HIIT for a full stomach!But jogging while fasted is a great way to just shred fat!)

This can all be kind of complicated, so let’s explain it more in-depth!

Understanding Fasted Cardio

Fasted cardio is a special version of cardio where the exercise is done in a fasted state. For example, taking a run in the morning without eating breakfast or a snack. Basically, you’re exercising on an empty stomach.

We will first have to understand how glucose works in our body. Glucose is like the energy source of the body. When you eat food, it gets digested and glucose is released into the bloodstream. When you hit the gym, and start lifting, your muscles call for glucose. The glucose reacts with oxygen inside the cells to produce energy. It is this energy that is used to lift at the gym or do any other work. 

Now let us consider what happens when we do fasted cardio. During fasted cardio, we haven’t eaten in a while.

Notice that because of this, there is no glucose intake and your blood glucose is very low- this means your muscles will be kind of starved of energy.

How will the muscles lift during fasted cardio, then? The answer lies in the fat that’s stored in the body.

Body fat can be stored and used for energy in a process known as ketogenesis. So when you go to the gym after your fast and start exercising, all that energy is actually coming from the body fat that you have on you.

Repeatedly engaging in fasted cardio will lead to a loss of fat. 

Does Fasted Cardio Burn Muscle?

Fasted cardio, as we’ve seen, burns a lot of body fat quite quickly. But what about muscles?

Does fasted cardio burn muscles too? According to some studies, exercising on an empty stomach leads to some loss of muscle. Many bodybuilders take amino acids before they do fasted cardio to help prevent this.

You see, for your body to start breaking down muscle- it needs to know there is little protein presence in the blood. In fact, such a little amount of protein/amino acids that your body just starts getting rid of muscle to get protein back in the blood.

Taking amino acids is a good way to help reduce this muscle loss. You simply just mix in a small scoop of the tasteless powder- kind of similar to creatine- into your water. This will put amino acids back into your bloodstream, reducing your chance of losing muscle.

Some people fast for their religion- and it’s actually common practice for many to take BCAAs every night of their fast to stop/reduce muscle loss. Most religious communities have no problem with this as this doesn’t break the fast in any way, as it’s a tiny powder of little proteins.

It doesn’t stop your fast or make your hunger change at all- it just puts more protein in your blood so you lose less muscle.

But the rate isn’t really comparable to the loss of fat. You see, in fasted cardio, there is no glucose with the body to work. This is why the body starts converting fat into energy.

Does Fasted Cardio Burn Muscle?

Why Does Fasted Cardio Not Burn Muscle? 

Fasted cardio is exercising after a prolonged period of fasting. Your body does not have any glucose during this period and is reliant on body fat.

‘That’s right, the body fat is converted into energy through a process known as ketogenesis and that’s how the body gets its energy during this period of low glucose.

HOWEVER, as I said earlier, your body CAN burn muscle if you have a low presence of protein. So if you haven’t been eating the daily recommended value of protein the past few days, it is more likely you’ll burn muscle. So, eat your protein every day so your body doesn’t feel the need to ‘borrow’.

Notice that in the whole process there is no mention of muscles except when they have to use energy. This is the simple reason why muscles are not burnt during fasted cardio. Instead, performing regular fasted cardio will give you a shredded, 3D look since fasted cardio works usually on the fat. Once the fat is burnt, one gets a very muscular, shredded look. 

Things That Actually Burn Muscle (Avoid These!)

Worried about burning muscle? Avoid these things if you want to keep that shred.

  • Diet:
    • Your diet is your number one source of maintaining your muscle mass. Conversely, it is also the number one source to lose muscle mass if you want to. Undereating and lowering your protein intake is a surefire way to burn muscle- keep your calories and protein higher if you want to keep muscle. If you’re trying to lose weight, lowering your calories by a little is okay, but anything drastic will cause the muscle to deteriorate.
  • Lowering/Avoiding Weight Training:
    • Want to keep muscle? Keep the weight and intensity high at the gym. Decreasing your weight or intensity is a surefire way to get rid of your muscle. Even if you’re trying to lose weight, keep going to the gym!


Fasted cardio, introduced in 1999, has gained so much traction in the bodybuilding world.

Fasted cardio works by forcing the body to function on body fat. When the body doesn’t get any glucose, it starts to break down fat for energy.

It is clear from our explanations that while there is a minute loss of muscle, largely, fasted cardio does not burn muscle.

If you’re seeing some muscle loss, try taking some BCAAs or eating more protein before your fast or before you go to sleep. This is actually common for those that religiously fast- they take BCAAs every night before they sleep as this is usually allowed within religious communities as it isn’t technically breaking any fast.

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