Nutrition > Fasted Cardio & How it Works
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Fasted Cardio & How it Works

4th Oct 19

Fasted cardio is a relatively new fitness trend that seems to be gaining a lot of traction. People are convinced that it’s working for them to cut down on their body fat percentages, and even more so than the usual fuelled workouts. We’re here to take a look at how effective this is really supposed to be, and what the ions and outs of it really are.

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What is Fasted Cardio?

Woman running

For anyone who’s not quite sure what fasted cardio actually is, never mind the benefits of it, this is the place to start. Fasted cardio from a general perspective is doing cardiovascular exercise in a fasted state, as the name suggests. Specifically, it means exercising when you haven’t consumed any calories in the past 4-12 hours. That means the prime time for it is as soon as you wake up, before breakfast.

What Does It Do?

The whole premise of fasted cardio and one of the supposed biggest benefits is that it burns fat directly. When you exercise as you likely know, your body is burning calories for energy. The idea here is that when you don’t have any calories to burn, you go to stored energy. Instead of all of the energy coming from your food that day, it’s going into your reserves. That comes from fat stores. As you exercise, you need the fat from these places to keep you going. That’s where all of this started and can be why it’s so useful to some people.

Does it Work?

This one is tricky and for a few different reasons. First of all, the science. Multiple studies have been done from a lot of different places. Most of them are pretty credible, too, which makes things confusing. Some studies (see below for all studies mentioned) suggest that it was effective, and others not so much. It may have to be a trial and error situation for you as an individual.

Is it Safe?

Before you do anything to do with fasted cardio, we have one last thing to look at, and that’s the risks behind fasted cardio. There’s always something to think about after all. No exercise is perfect, and you need to know what you’re up against.

Less Energy During Workout is Possible

First of all, the whole idea behind fasted cardio is using stored energy. Fat doesn’t always burn as quickly as you’d like it to. You may find that without your perfect mix of carbs fats and protein, you could be a little drained (and extremely hungry) during your workout. If that means you slack off a little, then it may not be as good for you as you might think.


This often goes without saying, but seriously, if you haven’t eaten for hours and you’re putting a lot of stress on your body, it’s not uncommon to feel a little light-headed. Be extremely careful in whatever you decide to do. That last thing you want is to be fainting or feeling ill without any food around. It’s pretty dangerous. Don’t jump straight into it, dip your toes first.

Hard to Stick To

Putting yourself in a fasted state to do exercise might not be the ideal state for you to be in personally. If you find it difficult to stick to or you love your breakfast to start your day, trying to make fasted cardio your new workout plan is not going to be easy to stick to. If it’s making training miserable or it’s just not for you, then don’t do it. Everyone likes to train differently, and you need to stick to it long term, after all.

Burn Muscle Mass

Last but not least, you need to be thinking about how it’s going to affect your body. Fasted cardio is, of course, going to burn some fat, but how is where things get a little complex. Without the simple carbs, complex carbs (check out the difference here), fats, and protein balance you usually work with, your body will react differently to exercise. You may be making fuel from the wrong places. That can even lead to muscle loss, or just not working effectively.

Ultimately, it has its pros and cons, as most training styles do. It might work for you, and it might not. One of the key takeaways in all of this variation is that everyone is different. This is vital to remember. The same thing does not always work for everyone. There are so many different factors in your composition; one exercise technique can’t be feasible for the whole world. That’s just a good thing to know.

If you’re set on trying it, wean yourself off breakfast as you work out first of all instead of diving straight in. Take your time to adjust and see how it makes you feel. Don’t try HIIT training or anything either, as that really need carbs. Fasted cardio is better set for LISS, as that’s the best heart rate zone for your body to break down and use fat (it’s a slower process than other calorie breakdowns). Take it easy with stair climbing, jogging, light cycling, cross-training, or anything else. Just don’t go all out, or you’ll be way more likely to see the adverse effects.

For more info about this topic, check out some of the studies we’ve looked at here:

man doing lunges

Before beginning any exercise or nutrition program, consult your physician, doctor or other professional. This is especially important for individuals over the age of 35 or persons with pre-existing health problems. assumes no responsibility for personal injury or property damage sustained using our advice.

If you experience dizziness, nausea, chest pain, or any other abnormal symptoms, stop the workout at once and consult a physician or doctor immediately.