Can you run a marathon on a Keto diet? This is an interesting question. There are a lot of things that go in your body when you are doing a Keto diet. So, the question is can a marathon be run on such a diet?

One can run a marathon on a Keto diet provided they have practiced their marathon training with the Keto diet. In such a case their body will be in ketosis and will be able to use the released ketones for energy.

Can you run a marathon on a keto diet

Marathon and Keto Diet

The Keto diet has become very popular in the last couple of years among weight watchers. Most of them swear by it and see it as their one-stop solution for their weight problems.

When your body is in ketosis, it has a good supply of ketones. Ketones can provide enough fuel to sustain a run. However, will it be sufficient to run a marathon while on a Keto diet?

Doing keto while running for marathon

The answer to this is that it depends…

Marathon requires a humongous calories to sustain through the race. If you can get enough amount of calories from fat and protein then you will be able to run a marathon with the keto diet.

However, the main thing to succeed with this is to practice…

A Keto diet requires a complete change in your lifestyle, especially your diet.

So, initially, your body won’t be able to cope with this sudden change…and will show some side effects like

  • Bloating
  • Nausea
  • Headache, etc.

This is often termed keto flu… This is when your body is getting adapted to the Keto diet…

Also, since there is less supply of carbs, if you are a runner, your body’s natural performance will go down until your body can go into ketosis.

So, if you suddenly start a keto diet and want to run a marathon, then you will not be able to…

Your body will hit the wall too soon and your marathon will remain unfinished…

What to do if you want to run a marathon on a Keto diet?

To run a marathon on a Keto diet, train for the marathon while on a Keto diet. This way your body will be in ketosis right when you would need it.

As with anything, don’t try anything new on race day. If you want to run a marathon on a keto diet, you will have to be in ketosis when you are running the marathon.

It is best to go on the keto diet right when you are starting to train for the marathon…if you don’t want to do that, start the keto diet at least 4 weeks before the marathon.

There is something called fat adaptation that your body goes through when you are on a keto diet. For that, your body needs a minimum of 4 weeks times.

So, start your keto diet with at least that much time in hand. However, be prepared to have a performance dip right after you start the diet as your body is gradually shifting from using its glycogen store to ketones.

marathon running on keto

Also, know that any food that you have is made up of protein, carbs, and fat. No matter how hard you try to avoid carbs, it is not possible completely.

Most of the foods that you will consume will have some amount of carbs in them…take a look at the table below…


Food Item (Quantity) Calories Carbs Protein Fat

Chicken Breast

(100 gms)

165 0 gms 27 gms 14 gms
White rice (100 gms) 129 28 gms 2.7 gms 0.3 gms


(100 gms)

402 3.1 gms 23 gms 33 gms
marathon run and keto

Side effects to consider

The Keto diet is not good in the long term if your activity level is low. It may give rise to cholesterol problems. However if your activity level is high, like that of a marathon runner, it may not create a problem. Also, one thing I don’t like about the keto diet is it restricts a complete food group which in itself is not good. But everybody is different…what will suit you may not suit me and vice versa… So, if you are planning to run a marathon on a Keto diet, please go ahead and give it a try. If it works for you, it is great, otherwise, you can return to your normal food habits.
Run marathon on keto diet
Madhusree Basu

Madhusree Basu

Author, Admin

Blogger and a fitness enthusiast. She loves running and Yoga and everything in between. She started running to manage her weight and to eat to her heart’s content. A true foodie at heart she shares whatever knowledge she has gained throughout the years about weight management and fitness.

Sourav Sarkar

Sourav Sarkar

Reviewer, Certified Fitness Instructor

Certified fitness trainer and an ex-professional bodybuilder, he has trained more than 500 fitness enthusiasts and has more than 15 years of on-the-job experience.