It promises a loss of several kilos in just two weeks. What is the principle of the Thonon diet? It is an extremely restrictive slimming method.
The Thonon diet is a very strict low-calorie diet to be followed for 14 days, then extended by a stabilization period.
It involves a strong calorie restriction (600 to 800 kcal per day, which is less than half of daily energy needs), a high intake of lean protein and a very strong restriction of carbohydrates and fats.
The meals are not very varied, and leave no room for the unexpected. In addition, the pleasure of eating is almost excluded.
The stabilization phase can be long since it is recommended to follow it for one week for each kilo lost. I explain here exactly what it involves and what its limits are.
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The first 14 days: extreme restriction
Here is a typical day on the Thonon diet, to be followed during the first 14 days:
Breakfast
- sugar‑free drink (permission to add a little milk only 2 days out of 14 days)
- permission to add a small multigrain roll 6 days out of 14 days
- permission to add 100 g of grated carrots 2 days out of 14 days
Lunch
- 2 eggs or 1 large steak or fish or chicken
- unsalted, unseasoned vegetables at will 10 days out of 14 days
- fruit at will 4 days out of 14 days
- a piece of cheese 2 days out of 14 days
Dinner
- 1 large steak (or 3 small ground beef patties) or cooked ham or 1 steak or 2 eggs or 1 plain yogurt
- unseasoned vegetables at will 8 days out of 14 days
- fruit at will 2 days out of 14 days
- 2 “joker” meals for enjoyment
As you can see, the meals are quite monotonous and above all contain few calories, fats and carbohydrates. You will definitely be hungry!
The stabilization phase
The stabilization phase offers typical days at 1200 calories per day for women and 1500 for men, still well below the body’s real needs.
Meals may seem more varied, but they still contain little fat and almost no carbohydrates.
What worries me about the Thonon diet
As a nutrition professional, several points concern me:
- the risk of nutritional deficiency: very insufficient intake of vitamins, minerals, fiber, essential fatty acids. Not just over 14 days, but also for the entire duration of the stabilization phase.
- the loss of muscle mass: even with increased protein intake, reserves will not be able to meet energy and micronutrient needs.
- the risk of fatigue or even infection with greatly reduced nutritional and micronutrient intake.
- the risk that food will become obsessive: which is very common when you do not consume enough energy, because this is a mechanism the body uses to demand the energy it needs from you.
- rapid weight regain after stopping the diet: what happens most of the time after a restrictive diet. In fact, the sudden reduction in the quantities consumed lowers the metabolism (a decrease that then persists over the long term). Not to mention that the weight lost during the restriction period would actually represent more muscle mass and water than fat mass.
The stabilization period also worries me. It is just as restrictive and can be quite long, since it is recommended to follow it for one week for each kilo lost (it is stated that the Thonon diet can make you lose up to 10 kg in 14 days).
From experience, after a diet phase as restrictive as the first phase, it is difficult to maintain a stabilization phase that is also so low in calories. The yo-yo effect (regaining weight after a diet) would thus be reinforced.
Risky situations with the Thonon diet
It is clearly stated on the Thonon diet website that it is not suitable for children, the elderly, pregnant women, and people “with fragile intestines”.
I would add that it is also to be avoided during breastfeeding, in the case of chronic disease, long-term medical treatment, fatigue, and a history of restrictive dieting. You can of course seek advice from your doctor.
Since 2010, ANSES has been warning about the dangers of weight-loss diets and the risk of weight regain in 80–95% of cases.
Moreover, this type of eating practice does not encourage long-term changes in eating habits and lifestyle. Yet this seems to me absolutely necessary for good weight management and to support one’s health.
Our dietitian offices are full of people who have chained together miracle methods… They then regained more weight than they had lost. The risk is then maintaining a complex relationship with food.
Don’t fall into this trap! It is not necessary (and especially not desirable) to restrict yourself so much to lose weight in a sustainable way!
Sources and scientific studies
- A typical day on the Thonon diet: https://regime-thonon.com/menu-regime-thonon-programme-minceur
- ANSES report (2010) on weight-loss diets: https://www.anses.fr/fr/content/regimes-amaigrissants-des-pratiques-risque
