Fasted Running

Fasted Running – Benefits & Drawbacks of Running on an Empty Stomach

With the rise of running as a form of fitness activity. More and more people are taking up this form of exercise. However, since most people start running as a way to lose weight, it is not surprising they try fasted running.

Many people think that fasted running can outweigh the benefits of running after eating. However, is this true? Is fasted running a good idea?

In this article we discuss:

– Fasted Running
– What is considered fasting
– What is fasted running
– Is it ok to run fasted
– How long should you run fasted
– Is it ok to run fasted in the morning before breakfast?

So if you want to learn any of the above, and apply it to your running, continue reading.


What Is Fasted Running or Cardio?

Fasted running or cardio is when you exercise on an empty stomach, which means to exercise fasted, you must have digested your meal before exercise. Generally, it needs to be digested and absorbed at least 3-5 hours before exercising. Doing so will mean your insulin levels are at their lowest.

In most studies, the best way to exercise or run fasted is first thing in the morning. Because you are exercising before the first meal of the day, your body will already be in a fasted condition from not having eaten for 8-12 hours.

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However, it is important to note that training fasted isn’t promoted by all coaches and researchers as some of the literature is against the theory behind running in a fasted state.

Some studies claim that you will burn more fat during exercise if you haven’t eaten before, while others show that you burn more if you exercise 1-2 hours after eating.

One of the best ways to find out if it works for you is to try fasted running or cardio yourself.

If you are trying fasted cardio for the first time, make sure you keep the intensity to a low to moderate effort. Make sure you only exercise for up to 1 hour, as your glycogen stores (energy) will start to run low. Then as you get used to it, increase the intensity, and duration.

We recommend if you are trying to exercise without food for the first time, keep track of what running you do fasted. You can do this by making notes in Training Peaks, an app, or in a google calendar. Then you can look back and see what effect it has had on your training.

How Long Should a Fasted Run be

How Long Should a Fasted Run be?

Now you may be thinking, I can run fasted without any problems. Even though most people can, running more than 1.5-2 hours will cause more harm than good.

While for most people, running 2 hours fasted isn’t difficult. The problem is the delayed recovery from the lack of glycogen, muscle breakdown, and fatigue caused by a lack of carbohydrates in the body. This will generally slow down recovery between runs and affect the upcoming training.

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So the ideal distance of a fasted run should sit between 1 and 1.5 hours. There are also some advantages of doing HIIT workouts fasted over long runs.

For example, high-intensity workouts have been shown to increase energy expenditure after a session. That means doing HIIT can benefit someone looking to lose belly fat or weight.

However, it is important to note that not everyone can tolerate high-intensity exercise well, so make sure you test before making it a regular thing.

Is it OK to Run Fasted in the Morning?

Is it OK to Run Fasted in the Morning?

Running fasted in the morning is still being debated today. Some say it has been proven to be the best time to with an empty stomach. Since your body has already digested its last meal an hour ago, your body will already have a low glycogen store. Making it easier for the body to use fat as an energy source.

However, other people and studies have shown that your cortisol levels are highest in the morning. Meaning that running on an empty stomach can affect cortisol levels, thus increasing muscle loss and weakness. Which in the long turn will negatively affect your muscles.

Is it Okay to Run While fasted? – What Do the Studies Say?

Some people swear by running fasted, while others don’t agree. Either way, there are a lot of studies that are both for and against this type of training.

One study from the Scandinavian Journal of Medicine & Science found that fasting had a negative impact on intensity and duration. This means that exercising on an empty stomach will end up hindering your performance in the long term. This is largely due to our dependence on carbohydrates.

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However, there is an argument against the above study. An older study from the Journal of Applied Physiology found that training in a fasted state for six weeks improved their endurance over those who ate food before working out.

Remember, running isn’t just about burning fat or losing weight. Many people want to see their times or speeds improve. So while there is a lot of advantages and disadvantages to fasting, it is wise to trial it before fully committing to the cause.



Before you completely disregard fasted cardio or running or even jump on that bandwagon, make sure you do your research. It is always wise to trial a few runs to see how the body copes. Doing so will prevent any long-term problems that affect your training.

Alternatively, if you are one of the people that struggle to eat before workouts out, you may not have a choice. If that is the case, try to shift your long or hard runs to the evening when your body’s glycogen levels are higher.

Either way, if you see your form start to plateau or decline, you are doing something wrong. If this is the case, reach out to a running coach or personal training who can help set you in the right direction.

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