In recent years, the ketogenic diet, or “keto,” has become very popular. It appeals to both people who want to lose weight and athletes. This diet is based on a drastic reduction in carbohydrates in favor of fats. It causes a profound change in energy metabolism. The body then functions in a state of ketosis: with carbohydrates depleted, it draws its energy from fats.
Some athletes notice an improvement in their endurance with this diet. Others, on the contrary, notice a decline in their performance.
What is the ketogenic diet?
The ketogenic diet is very low in carbohydrates (5 to 10% of daily requirements), high in fat (70 to 80%), and moderate in protein (15 to 20%).
The goal is to push the body into a state of ketosis. In this state, it uses fat as its main source of energy instead of carbohydrates.
This approach is very different from a traditional diet, where carbohydrates remain the main source of energy.
1) The purpose of this diet
The main objective of the ketogenic diet is to alter the body’s energy metabolism.
a) To enter ketosis
Reducing carbohydrates to less than 50 g per day quickly depletes glycogen stores (glucose stored in the liver and muscles). The body must then find an alternative source of energy. It converts fatty acids into ketone bodies in the liver. These molecules become the main fuel for muscles and the brain.
b) Optimizing fat utilization
In ketosis, the body learns to use its fat reserves more efficiently. Even a thin person has more fat stores than carbohydrate reserves. The idea is to have more sustainable energy without needing to constantly replenish carbohydrates.
c) Encouraging body fat reduction
Since the metabolism runs on fat, the ketogenic diet promotes weight and fat loss. Ketosis also limits blood sugar fluctuations, reducing cravings and prolonging the feeling of fullness.
d) Maintaining steady energy levels and concentration
Some users report less fatigue due to fluctuations in blood sugar. Ketone bodies provide constant energy to the brain, sometimes improving concentration.
2) Origins and Applications of the Ketogenic Diet
The ketogenic diet was developed in the 1920s to reduce epileptic seizures in children who were resistant to medical treatment. Today, it is used in other medical contexts (type 2 diabetes, obesity) and has become popular in the fields of wellness, weight loss, and sports.
3) Why is this diet used by some athletes?
- Prolonged endurance: glycogen stores (glucose stored in the liver and muscles) are limited, whereas fat stores are nearly unlimited. This provides a more stable source of energy over long distances and helps delay fatigue caused by the depletion of carbohydrates.
- Better weight management: the body more easily draws on fat stores, which can lead to increased fat loss. The ketogenic diet also reduces snacking cravings and enhances the feeling of fullness, as fats and proteins are more satiating nutrients than carbohydrates.
4) The limitations of this diet for performance
Even though the ketogenic diet offers certain benefits, it also comes with significant constraints for athletes, especially those participating in disciplines that demand power or explosiveness.
a) Reduced performance during high-intensity efforts
Sports such as sprinting, weight training, or CrossFit require rapid bursts of energy. Ketosis limits the availability of carbohydrates. Ketone bodies provide energy more slowly, which can reduce speed, strength, and power.
b) Difficult adaptation period
When the body transitions into ketosis, several complications may occur:
- Fatigue, headaches, irritability, digestive issues.
- Adaptation period lasting from a few days to several weeks, depending on the individual.
c) Slower recovery
Carbohydrates play a key role in replenishing muscle glycogen after exercise. During a ketogenic diet, the amount of glycogen available is very limited, which can slow down recovery
d) Potential risk of nutrient deficiencies
Drastically reducing certain foods such as fruits, grains, or legumes can limit your intake of fiber, vitamins, and minerals. These micronutrients are essential for performance, recovery, and proper metabolic function.
The ketogenic diet is a radical but structured approach to nutrition. It promotes the use of fat as the main source of energy.
For some amateur athletes or Kinomap users, it can help to lose fat mass. But it also has significant limitations that should not be overlooked.
It is not suitable for everyone, particularly high-level athletes or those involved in sports that require power and speed.
This is not a miracle solution. When personalized, tested gradually, and supervised by a healthcare professional or nutritionist, it can be a useful tool.
Chloé Masson
Nutrition Project Manager
chloemasson.nutrition@gmail.com
See previous nutrition articles :
VEGETARIAN DIET FOR ATHLETES : IS IT POSSIBLE ?
THE IMPACT OF ULTRA-PROCESSED FOOD ON YOUR BODY
ANTI-INFLAMMATORY NUTRITION