Fasted Cardio….Good or Bad?

Fasted Cardio….Good or Bad?

For many of us, whether we are physique competitors, models, or just every day individuals, our primary goal is to loose as much bodyfat as we can. An ongoing debate within many health and fitness forums, and between many professionals in the industry is whether “fasted cardio actually works, and is it safe?” In this article I will examine this subject.

What is fasted cardio?

As the title states “fasted” cardio is done first thing in the morning and on an empty stomach. Unfortunately, there is little specific research to back up either side of the argument. Some research suggests that fasted cardio may cause severe loss of muscle due to catabolism because the muscles are working in a depleted state. Without nutrients to repair the damage caused from exercise the muscle begins to break down and is used for energy. On the other hand, a slight loss of muscle will help you lose weight, if that is your goal.


In the case of physique competition and fitness modelling, muscle loss should be avoided as much as possible.

Muscle repair

After sleeping, the body uses glycogen in muscles for energy. It takes between 24-48 hours to be completely depleted of glycogen and reach a state of ketosis, but depletion can start occurring after 4-8 hours. This means that when you wake up you are generally using a combination of fat stores and muscle breakdown for energy.

Being in a glycogen depleted state causes acidity in our body, which can put excess stress on our immune system while potentially damaging our cells and muscles. In turn, this makes muscles more vulnerable to injury and our body less absorbent to nutrients. On the other hand, training in this state does influence fat burning by turning to our fat stores for energy.

Fasted Cardio….Good or Bad?

Muscle breakdown occurs when the body is in a glycogen depleted state, forcing it to use fat and muscle as energy. When we exercise we are tearing small muscle fibres and producing lactic acid. The proper nutrition will help recover and repair.

Conclusion, does fasted cardio work?

Taking everything here into consideration. I, personally would recommend doing fasted cardio. However, the individual in question would also be told to use a BCAA (branch chain amino acid) powder supplement to stop the muscle breakdown. The job of BCAA’s is exactly that, to prevent muscle breakdown. I would also advise that BCAA powder be mixed with a carbohydrate powder such as Meltodextrin as this will provide an insulin spike to the body, and save a fair bit of muscle breakdown. If these supplements are used, then this form of cardio can be extremely effective whether it be Steady State Cardio, or High Intensity Interval Training.