The Truth Behind the 'Keto' Diet

Multiple people (male athletes) have approached me lately asking about what they call the 'keto' diet. It seems as though it's becoming more and more popular among various types of athletes and my question is why? Combined with what I know, I did a little research and here is what I found...Read on.

Glucose is the body's main source of quick energy and your brain's preferred source of fuel because it is quick to breakdown and easy to access. It is stored in both the liver and muscle as glycogen. If you remove carbohydrates from the diet, fat metabolism increases because your body needs fuel from another source.

Athletes following a ketogenic diet aim to put their bodies in a state of ketosis, meaning instead of using glucose as the main source of fuel they use fat. In order to do this, the diet must be extremely high in fat and low in both carbohydrates and protein. To reach ketosis about 75% of calories should come from fat and 25% from carbs and protein. Most of the research notes that people typically feel tired, weak, and even nauseous their first few weeks as their bodies enter into ketosis. However, these symptoms do reside after a of couple weeks.

Fat requires more oxygen than glucose to breakdown and be used as fuel. Therefore, in anaerobic exercise (short, high-intensity - sprinting, heavy lifting, etc.) your body requires glucose to fuel those quick bursts of energy because it does not have enough oxygen to catabolize fat. In aerobic exercise your body is able to use more fat as a source of fuel because it is taking in more oxygen. These are typically longer endurance types of exercises. During the course of your exercise, your body typically goes through both anaerobic and aerobic metabolism.

Some athletes believe following a ketogenic diet will allow them to perform stronger and longer by using fat as their main source of energy. To date, no study has shown ketogenic diets to improve athletic performance.


I just returned from FNCE (the national Food & Nutrition Conference & Expo) at which I was lucky enough to hear Dr. Hawley speak about his many studies involving olympic athletes and the ketogenic diet. Dr. Hawley and his colleagues put olympic athletes (speed walkers) on various types of diets - including either a high carb or a high fat diet. They repeatedly found the athletes on the HIGH CARB diet to have the most IMPROVED performance while the athletes on the HIGH FAT diet showed NO IMPROVEMENT at all. It is much more efficient to allow your muscles to use glucose as a fuel. When your body becomes fat-adapted it actually impairs the muscles ability to use the most efficient fuel source (carbohydrates!). 

Like any diet, the ketogenic diet is not particularly sustainable. 

You can function off of ketones and without carbohydrates but you would be lacking essential vitamins and minerals by eliminating fruits and vegetables. If you are considering following a ketogenic diet, I would strongly encourage working closely with a registered dietitian.

There are a variety of reasons to adopt a ketogenic diet, however, it does not seem to improve athletic performance. The ketogenic diet IS effectively used to treat and eliminate seizures in children (although it has shown to be less effective in adults); I do support it in this context but again recommend consulting a dietitian for help.