Ketogenic Diets: Are They Effective For Endurance Sports?

Our friends Crown Sport Nutrition, a brand specialized in sports nutrition with cutting-edge products, continue to provide us with knowledge on, for example, how to improve our sports performance through food.

On this occasion they tell us about a current topic, the ketogenic diets and athletic performance.

What are ketogenic diets?

The ketogenic diet, also known as the keto diet, is a diet that consists of a low consumption of carbohydrates and rich in fats.

Simplifying, what this diet does is reduce carbohydrates (to less than 50 grams a day) and replace it with fats or proteins exposing the body to ketosis.

The diet aims for the body to become efficient and learn to convert all fat into energy, which is ideal for endurance sports.

This type of diet has gained great popularity in recent years both in the world of sports and in the general population.

The amount of carbohydrates that are recommended in this diet are less than 50 grams per day and replace them with fats or proteins with a minimum of 0.8 - 1.2 g / kg / day

Why do athletes choose this diet?

Surely on some occasion you have heard that an athlete performs this type of diet. There are many reasons why it is started to be used, such as weight loss or improved sports performance

What does science say about endurance sports and the ketogenic diet?

As usual, Crown Sport Nutrition relies on the latest scientific studies to create new products or combine existing ones to increase their effectiveness. In this case they have done the same.

If there is a physiological basis that may suggest that ketogenic diets could "accustom the body" and decrease dependence on carbohydrates, thereby increasing the ability to use fat during exercise.

This is interesting for endurance athletes, since in this type of sport such as Ironman, cycling or trail running, carbohydrates are the main source of energy that athletes have.

There is evidence indicating that ketogenic (low carbohydrate) diets increase fat oxidation and decrease carbohydrate utilization, especially when performing low intensity exercise, something applicable to endurance sports.

Study on cyclists

In a study conducted with cyclists in a 100-kilometer test where one group followed a ketogenic diet (6% carbohydrates) for 12 weeks and another a high carbohydrate diet (65% carbohydrates) it was shown that the ketogenic diet did not it only increased fat oxidation during the test, but also increased performance in a test carried out at the end of those 100 km.

Although these early results were promising, other studies to prove it have not found such benefits.

Study reviews

A review of 17 studies concluded that ketogenic diets are not beneficial for endurance performance.

In fact, in other studies conducted with elite athletes, it has been shown that following a ketogenic diet for 3 weeks results in a deterioration in performance and economy of effort at competition intensities

The ketogenic diet and strength sport

In addition to the study in endurance sports, the use of this type of diet has also been studied in strength sports such as CrossFit.

In this type of sport, it could be expected that reducing carbohydrates could be harmful, although in the study mentioned above it was found that out of 16 tests only 2 obtained benefits when using this diet. Neither negative effects nor improvements were observed in the rest.

Body composition or weight loss with ketogenic diets

As we have mentioned before, one of the reasons why athletes use this diet is weight loss.

To verify its effectiveness, a meta-analysis of 13 studies was carried out where the effects of ketogenic diets were analyzed together with strength training in body composition.

The results of the meta-analysis showed that the ketogenic diet significantly decreased body weight (3.7 kg on average) and fat mass (2.2 kg on average), but also muscle mass (-1.3 kg)

It should be taken into account that in these studies the participants performed strength training.

This was verified in another study with bodybuilders where it was observed that the use of this diet was associated with a greater loss of fat than in normal diets.

These results are confirmed in a recent study carried out in bodybuilders that observed that, although the ketogenic diet was associated with greater fat loss than a "normal" diet, only those who followed a normal diet increased muscle mass, although in both groups they improved strength in a similar way.


In conclusion, the evidence to date does not show that ketogenic diets have performance benefits in endurance sports, although there is when used in the pursuit of weight loss.

However, it must be taken into account that using these diets can cause a greater loss of muscle mass, so it will be essential to control protein consumption.


Peter Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR, Madrid).

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