The Thonon diet is one of the drastic diets that is depopulating both in Europe (France and England in the first place) and in the United States : it is a diet that promises to lose about 5-6 kilos in the first two weeks, and another 3- 4 kilos in the two-week maintenance regimen or stabilization phase. In theory, this stabilization phase should last until all excess weight is lost, and should cause you to lose about one pound per week. Despite the success of the diet, the diet has no known origins, it is not endorsed by any doctor but by a site, this one, where the menus are explained day by day. According to the same site, the diet was developed by the French medical center  Thonon-les-Bains Hospital ,  hence the name, but the center has never made the diet official.

What does it consist of and why is it not recommended?
The Thonon diet includes a very restrictive two-week shock phase: for breakfast the first day includes only bitter coffee or tea or with zero-calorie sweetener, for lunch two eggs with green leafy vegetables without salt and without added oils. Then directly dinner with a steak or two and a salad with celery and lemon juice. The second day includes a veal burger, oil-free salad and fruit for lunch, and cooked ham only for dinner. You can stain the coffee with a little milk. The third day is the same as the first, and from the fourth for breakfast you can add a slice of wholemeal bread. From the fourth day the pattern is as follows.
Breakfast with coffee and a slice of bread.
Lunch with salad with assorted vegetables, two hard-boiled eggs or a hard-boiled egg plus a piece of cheese, or fish with boiled vegetables without oil, or meat with vegetables without oil. For dinner, a white skimmed yogurt and fruit, or ham or meat or fish and vegetables.

The diet is very restrictive. It does not exceed 800 calories per day and is incompatible with anyone’s lifestyle, as well as promoting the loss of lean mass and metabolic slowdown, not to mention nutritional deficiencies. After 14 days of the same menu, in which I know she should have lost 5 kilos, we move on to the stabilization phase, which provides 1200 calories for women and 1600 for men.

The stabilization phase is the only barely permissible part of the diet, with a similar pattern.
Breakfast with unsweetened coffee or tea + a skimmed white yogurt or 100g of cottage cheese or a glass of skim milk + a slice of toasted wholemeal bread with a teaspoon of margarine + a fruit or a glass of unsweetened juice. Snack with 100 grams of cottage cheese or a small sour fruit. Lunch with meat or fish (100/150 gr) plus cooked or salad vegetables, a fruit, a skimmed yogurt or 100 grams of cottage cheese. Dinner with 100 grams of potato or a minestrone, a portion of meat or fish as for lunch or two eggs, vegetables of your choice.