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The keto (or ketogenic) diet is said to be dangerously hyper-protein and only good for fast weight-loss, that it has a bounce-back effect, and even that it considerably reduces sports performance. There are many rumors, and yet, over time, there are more followers. What is true or false in all of this?

We spoke with Mireia Quijada, sports nutritionist at Eat2win, so that she could bring us up to date. “The keto diet consists of reducing daily consumption of carbohydrates to less than 50g and increasing fat consumption. This way, you use your fat reserves instead of the carbohydrates as a source of energy.”

This means a significant reduction in foods that are high in carbohydrates, such as cereals, legumes and fruit, and introducing larger quantities of fats through dried fruit, meat, fish, avocados, coconut, eggs…

Advantages of a ketogenic diet

  1. Weight loss and detoxification, as a lot of fat from your fat deposits is burnt off. You also experience less hunger, as fats satiate you more, and for longer than carbohydrates.
  2. Reduces inflammatory processes in the body. You will quickly notice an improvement if you suffer from stomach bloating or water retention.
  3. Greater concentration.
  4. On a clinical level, it is being shown to prevent and improve autoimmune diseases such as epilepsy, Parkinsons, Alzheimers and cancer.

Disadvantages of the ketogenic diet

  1. Difficult adaptation: during the first days, you may feel unwell while you are making the transition from one energy source to another, that is from carbohydrates to fats.  
  2. Dehydration: a lot of liquids and sodium are lost, so you need to significantly increase your consumption of water and salt.
  3. Social complications, as it is rather difficult to maintain the diet when eating away from home.
  4. Reduction of vitamins from the discarded carbohydrates.  

And what happens to sports performance if you follow a ketogenic diet?
Marcos Vázquez, from the Fitness Revolucionario blog, is a real expert on the subject. In one of his articles, he explains that our carbohydrate reserves are low, while our fat reserves are immense, so to include a period on a keto diet may boost your capacity to access your large fat deposits as a source of energy, reserving the glucogen and the carbohydrates for high-intensity effort and thereby improve total performance.

The dilemma is right there, in high-intensity activities that depend almost completely on glucogens for fuel. It seems logical that in sports like Crossfit, the reduction in muscular glucogen may reduce your performance. Nonetheless, Marcos has analysed various studies in which crossfitters follow a ketogenic diet and he concludes that this is not the case: no study shows a reduction in performance after four weeks of adaptation, but they do show a greater loss of fat and an improvement in the body composition of muscle/fat.  

Additionally, as he explains, “it is certain that, in the short-term, the glucogen reserves remain lower when following a ketogenic diet. But a recent study shows how after several months of ketosis, glucogen reload becomes more efficient, thereby avoiding a very negative effect in glucolytic training”. The negative effect referred to is the production of lactate which is characteristic of glucogen consumption, as the lactate gives rise to the sensation of fatigue. 

Can crossfitters follow a ketogenic diet, or not?
You can, as there is no evidence that it reduces your performance or strength, but just as Fitness Revolucionario concludes, it is not a diet that will improve them either. 

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