Written by Justin Harris and Team 1D

What is Fasted Cardio?

Fasted cardio refers to doing a cardiovascular exercise, such as running or cycling, on an empty stomach or after fasting. On the other hand, regular cardio refers to cardiovascular exercise at any time, whether before or after eating.

What Are the Claimed Benefits of Fasted Cardio?

While there are some potential benefits to fasted cardio, such as increased fat burning and improved insulin sensitivity, the evidence is mixed and the effects may not be significant for everyone. Here are some potential benefits of fasted cardio compared to normal cardio:

1. Increased fat burning: When you exercise in a fasted state, your body may be more likely to burn fat for energy since lower levels of glucose and glycogen are available. However, the amount of fat burned may be similar to if you were to exercise after eating.
2. Improved insulin sensitivity: Fasted cardio may help improve insulin sensitivity, benefiting those with insulin resistance or diabetes. This is because exercising in a fasted state can increase glucose uptake by the muscles, which can help lower blood sugar levels.
3. Reduced bloating and discomfort: Some people may prefer fasted cardio because it can reduce bloating and discomfort during exercise, particularly if they have eaten a large meal beforehand.

Drawbacks of Fasted Cardio Exercise

1. Reduced energy: Exercising in a fasted state can lead to reduced energy levels, which can make it harder to complete a workout or perform at your best.
2. Muscle breakdown: When you exercise in a fasted state, your body may also break down muscle tissue for energy, which can lead to muscle loss over time.
3. Increased risk of injury: Fasted cardio may increase the risk of injury, particularly if you feel weak or dizzy due to low blood sugar levels.

The Truth About Fasted Cardio

The biggest point will just be getting the cardio in. There are no studies showing that there is a statistically significant difference in burning more fat doing cardio fasted vs. fed, but I do believe you can POTENTIALLY burn more fat while blood glucose levels are at their lowest (fasted/post workout).

Will you notice a difference if you do fasted cardio versus normal cardio for 10 weeks? No. Expand that to 10 years, and there may be a different answer.

When Should I Do My Cardio Workout?

Typically, I suggest doing all cardio post-workout. You're already at the gym, moving and sweating, and if there is a difference between doing cardio with lower insulin levels, you can take advantage of that. But the ultimate answer is no; it doesn't really matter. Just get it in. 

What Will This Style Of Cardio Do To My Muscle Mass?

We worry way too much about losing muscle. The human species would never have survived if we lost muscle after a walk without food. For much of our history, we were persistent hunters, meaning that the way we hunted before tools like arrows or effective spears was to chase animals until they died of exhaustion. One thing humans can do better than pretty much any species on earth is dissipated heat and travel long distances.

Our gait is extremely energy efficient, we have sweat glands to dissipate heat (we don't pant like a dog), and we have a large surface area to body mass ratio for dissipating heat. We were built to chase animals until they died; we won't lose muscle from a short cardio session.

Athletes and Their Body Composition with Cardio Exercise

This is obvious if you look at non-bodybuilding athletes who don't get inundated with the dogma of "you'll lose muscle" from exercising as we do, most high-level sprinters look more muscular than the majority of people devoting a large portion of their life to building muscle, and they don't devote any real effort into building muscle too much would just be wasted weight.

They don't panic about eating every 3 hours. They don't panic about burning muscle from their cardio. They just work their ass off, which, as blatantly obvious as it seems when you remove the veil of "you'll lose your gains bro" makes perfect sense, the harder they work out, the more muscular they look.