The main danger of fast diets is that they concentrate their effectiveness in excess of a certain type of nutrient and the lack of others which generate unsavory imbalances in the body. It surely thins you very rapidly, but at the expense of losing fluid, muscle and little fat, which is what really matters. In addition, at the end of the diet, the lost weight is recovered very swiftly. Depending on the type of fast diet, the risks are different and I have listed some risks based on the main rule of the diet.
Diets Low in Protein