ketogenic diet

Does the ketogenic diet really help you lose weight?

Losing weight by eating fat and excluding sugar: this is the surprising promise to say the least of the ketogenic diet. How does it work? Is it effective? We take stock.

Losing weight by eating fat: this is the surprising promise to say the least of the ketogenic diet. Used for almost a century against certain forms of epilepsy, the ketogenic diet has gradually made its way alongside weight loss diets. For some time it has had some success, as evidenced by the twenty or so books published in recent years and the numerous press articles which are frequently devoted to it. How does this diet work? What do we know about its effectiveness? Le Figaro takes stock.

What is the ketogenic diet?

The National Food Safety Agency (ANSES) considers that, for an adult, around 10 to 20% of energy must come from proteins, 35-35% from lipids (fats) and 40-55 % of carbohydrates (sugars). The ketogenic diet, for its part, is based on a drastic reduction in carbohydrate intake (no more than 50 grams per day for an adult) in favor of a massive intake of lipids (70 to 90% of total energy intake) , with a protein intake which remains at 15-20% of the intakes. Rather counter-intuitive, in a world where fat plays the wrong role in the collective imagination.Cereal-based foods (bread, pasta, rice), potatoes, ready meals, sweets, cakes and milk (rich in lactose, which is a carbohydrate) should be avoided. Certain fruits and vegetables, too rich in carbohydrates (a banana provides about 30 grams of carbohydrates out of the 50 required), are also to be avoided, as are legumes. However, you must bet on all foods rich in fat and proteins such as vegetable oils, butter, eggs, meats, oily fish, avocado, coconut or oilseeds (almonds, Hazelnut...). "In practice, it's a very difficult diet to follow," says Professor Luc Cynober, head of the biochemistry department at Cochin Hospital (AP-HP) and author of Everything about your weight, Don't take any risks! (Ed. Michel Lafon).

How it works?

To function, the body has three types of food fuels: carbohydrates, fats and proteins. When carbohydrates are very low - as is the case with the ketogenic diet - the liver begins to make ketone bodies from dietary fat or body fat stores. It is said that the body is in "ketosis": it turns into a machine to "burn" fat. Ketones therefore become the main energy source for most of our cells. This change occurs on average between two and four days after the adoption of the plan.

Does the ketogenic diet allow you to lose weight?

“The problem with these extreme diets is that there is a rebound effect. Often people are gaining more weight than they originally lost. ”

Pr Luc Cynober

"A drastic diet of this type certainly makes you lose weight," says Professor Cynober. “The individual can lose several pounds in a month. But the problem with these extreme diets is that there is a rebound effect. Often people are gaining more weight than they initially lost. ” The famous "yo-yo" effect, which is found in all diets.

“Studies have shown that low-sugar diets make it possible to lose weight faster than low-fat diets. But in the long term, the weight curves meet, "says Dr. François Jornayvaz, head of the diabetology unit at the Geneva University Hospitals and author of several scientific articles on the ketogenic diet.

According to the doctor, we must distinguish this diet - where carbohydrates are almost eliminated - from low-sugar diets. "We have reason to think that moderately low-carbohydrate diets, which do not exceed 130 grams of sugars per day, could be beneficial, especially for diabetic patients," he said. But we must be extremely careful about the type of fat consumed and favor those of vegetable rather than animal origin, otherwise there is a risk of developing fatty liver (fatty liver) and hypercholesterolemia, with harmful effects in the long term. "

For the moment, even if the promises of the ketogenic diet are spreading (weight loss, but also cancer, Alzheimer's disease, etc.), it must be remembered that its effectiveness has only been scientifically proven in epilepsy.

Are there any side effects?

In the short term, switching from a conventional diet to a ketogenic diet can lead to nausea, constipation, fatigue, headaches, cramps, bad breath ... These are all the inconveniences mainly linked to dehydration. "With this diet, the body is forced to use its glucose reserves," says Professor Luc Cynober. “However in the muscle, glucose is stored with water. Its use therefore leads to the elimination of water which contributes to weight loss but also to dehydration ”.

This diet, which involves a reduction in the consumption of fruits and vegetables, can also lead to deficiencies. "There may be a vitamin, mineral and fiber deficit," says Professor Cynober. Hence the need to take advice from a dietitian or a nutritionist before embarking on such a business.

In the long term, the consequences are poorly understood. Most of the scientific work done so far has focused on a small number of participants and / or does not include a control group for comparison. "The strongest data we have is from children with epilepsy," says Dr. Jornayvaz. "They show that there is ultimately a risk of developing kidney stones, osteoporosis and a growth disorder."