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Running: Running on an empty stomach, its advantages and disadvantages

 Running: Running on an empty stomach, its advantages and disadvantages

Running on an empty stomach is a way to change the type of running training. Some runners recommend it and practice it regularly. What are its effects on the body? Should this type of session be recommended systematically?

What is a fasting jogging session?

For a gym session to be considered "fasting", it usually takes 10 to 12 hours without having eaten before. why ? Quite simply because this period of time makes it possible to empty the reserves of glycogen in the liver (sugar reserves) and reduce the level of insulin. However, glycogen is still present in the muscles.

During sprint training, the body will initially derive energy from muscle glycogen stores. Once these reserves are relatively exhausted, the lipid (fat) reserves will be used as 'fuel'.

It is not recommended to perform high intensity exercise, especially if you are not used to it. A typical "fasting" running session generally corresponds to an output of between 70% and 80% of VO2 max for a duration of between 40 and 60 minutes.

More intense and/or longer sessions require a lot of energy, which is incompatible with being on an empty stomach. In this case, training will not help you.

Attention to diversifying the type of training

To improve athletic performance in long endurance activities, it is advisable to change the type of exertion. In fact, the body adapts to various demands.

During a 10-kilometre, half-marathon or marathon race, the body must rely on the various possible energy paths, namely:

  • Use your glycogen (sugar) buffers
  • Use of fat (fat) stores
  • Use protein reserves (muscle structure, proteins)
  • So it can be interesting to train the body to use each of these different pathways.

Short and intense training sessions (training with short intervals) will focus more on glycogen reserves, while longer, less intense sessions (from 50 minutes) will focus more on fat reserves.

Running on an empty stomach makes it possible to target the lipid pathway a little more and thus constitutes the possibility of a difference in the type of training chosen.

Note: No kind of effort pursues just one of these pathways in isolation.

Do you work on an empty stomach to lose weight?

Make no mistake about it, jogging on an empty stomach isn't necessarily the miracle weight loss solution.

This is for two reasons:

First, weight loss is related to the difference between the amount of calories stored and consumed. But training on an empty stomach is not the one that allows the most energy (calories) to be expended. More intense workouts (training in short intervals) increase calorie expenditure.

After that, food remains necessary. To lose weight, the demand for fat and sugar storage must be significantly limited. No need to conduct sessions on an empty stomach to allow yourself extra rich meals afterwards!

See also: What happens if you stop eating?

To sum up, training on an empty stomach is thus a good weight loss supplement but it is not enough on its own!


It is important to specify that this practice is not recommended for beginner runners because it requires knowledge of your body and its limits. The risk of developing hypoglycemia is limited but not insignificant. Know your effort in training.

Don't run on an empty stomach all the time. As we said, it is recommended to change the type of training, whatever your goal (performance, weight loss).

Your glycemic reserves should not be too low before you start training. Some runners who have not eaten enough food the previous day find themselves experiencing hypoglycemia (loss of consciousness, dizziness, impaired alertness, etc.). Previous meals should preferably contain slow sugars (whole grain rice, pasta, and other starchy foods).

In the same way, the general condition of fatigue is an important factor. The cumulative lack of sleep also reinforces the disorders just mentioned. This sometimes leads to minor injuries (sprains, falls due to inattention) but also leads to more serious accidents, especially when road training comes into contact with traffic.

So be progressive and don't start running with an empty stomach. Get to know yourself first, listen to your body and respect the ground rules so these workouts go well!

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