The Weight Will Just Come Back
Crash dieting is a piece of (rice) cake for a few days. Once the effects of extreme calorie, protein, carbohydrate and fat deprivation kick in, however, it becomes frighteningly easy to fall off the dieting wagon.
Metabolic function slows way down during crash diets, so once you start eating normally again, your metabolism simply can't operate at its previous rate. These excess, unprocessed calories are then turned into fat, and the pounds pile back on.