Hailed by several stars, the ketogenic diet offers to significantly reduce the proportion of carbohydrates in your diet and to favor fats.

But if it allows a significant weight loss, it is not without risk, as the nutritionist Catherine Lacrosnières recalled on Europe 1. 

Losing weight with a fat-based diet is possible, but difficult.

Gwyneth Paltrow, Kim Kardashian ... Many stars have praised the merits of the ketogenic diet in recent years, the program that may seem completely the opposite of traditional diets, since it offers no more and no less to eat mainly foods rich in fat.

But if the allowable weight losses are sometimes spectacular, this diet, extremely restrictive, is not without risks, as recalled on Europe 1 the doctor-nutritionist Catherine Lacrosnières, guest on Wednesday of Without appointment. 

What is it about ?

The program is therefore simple, less sugars and more fat.

"We are going to change the body's fuel and eat mainly fat, reducing a lot of sugars, which are usually the body's main source of energy," while keeping some protein, "but just what the body needs ", explains Catherine Lacrosnières.

In the classic diet, carbohydrates indeed represent between "40 and 55% of our daily calories" against 35 to 45% for fats.

With this new diet, the idea is to have "less than 10, even 5% of sugars intake", while we will increase the level of fat to at least 70%.

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The reaction of the body caused by this change in diet will cause weight loss.

To replace the energy usually supplied by sugars, the body "will transform fats into a metabolic intermediate, the ketone bodies, and it is they who will provide energy to the body", continues Catherine Lacrosnières.

"From the moment when we no longer consume sugar, in the first days, we will use what we have left of sugar reserves in the body, by glycogen, in the liver. This glycogen is linked to molecules of water, and as we use it, we will become dehydrated ".

It is this loss of water which will in the first place lead to an "extremely rapid" weight loss, describes the specialist.  

Then, "once you have no more of this glycogen, you will use the fats provided by the diet, but also those stored in fat cells, adipocytes, which will also turn into ketone bodies" . 

What is allowed, what is banned 

"It's an extremely restrictive diet," warns Catherine Lacrosnières, the intake of sugars should not exceed 50 grams per day.

All sugary products, most vegetables and fruits are thus banned, but also, unsurprisingly, sugary drinks, pastries, pastries, cookies, but also legumes and starches, cow's milk products, cheeses with paws. soft.

Of course, some fruits are still allowed, such as red fruits, less rich in sugar, or coconut and avocado.

On the vegetable side, we can continue to consume green vegetables, but not carrots or beets. 

The ketogenic diet will therefore consist mostly of fatty meats and fish, eggs, vegetable oils and oilseeds.

On the other hand, a high fat diet does not mean that all fats should be consumed at the same dose.

"We are going to advise what we call beneficial fats, with a saturated form", explains Catherine Lacrosnières.

No need, therefore, to rush to the cold cuts. 

Thus, a breakfast can consist for example of a coffee accompanied by an avocado and some olives, or an omelet, while at noon, "one can prepare a meat or a fish with a small portion of green vegetables such as beans, then eat coconut yogurt or a little hard cheese, "explains the nutritionist.

And for afternoon tea, the guest from Europe 1 offers for example "a nice handful of oilseeds, such as hazelnuts, almonds, provided you choose the unsalted". 

What are the side effects? 

Like most diets, especially the most restrictive, the ketogenic diet can be followed "by an even greater weight gain", the famous "yo-yo effect", recalls Catherine Lacrosnières, who therefore advises people following this diet to be followed by a specialist, and to take a blood test before starting.

Because, she specifies, "the ketogenic diet will risk increasing the level of total cholesterol and also that of bad cholesterol. It is therefore necessary to check if you are not already in a case of hypercholesterolemia".

This fat-based diet can also cause "headaches, fatigue, dizziness," says the nutritionist, not to mention early dehydration, and "loss of electrolytes": sodium, potassium, magnesium. 

It is therefore advisable to drink a lot at the same time, and to compensate for its losses.

Thus, continues Catherine Lacrosnières, we can prepare a broth to bring salt, spinach for potassium, and oilseeds for magnesium. 

Other deficiencies will be noted, in particular at the level of vitamins provided by fruits and vegetables.

Lack of fiber can also lead to constipation. 

There are also some contraindications for this diet.

Thus, it is strongly discouraged for people awaiting hepatic steatosis (fatty liver), or for pregnant women.