The recommended weekly weight loss is ½ to 1 kg, which corresponds to 500 fewer calories per day, which come from reduced food intake and physical exercise. A weight loss program that promises spectacular results in a very short period of time is definitely depriving and can cause disturbances in the metabolism. In these cases what is lost is not fat but mainly fluids and muscle mass. In addition, crash diets usually do not have stable results, as the weight loss can be quickly reversed and the person may even gain additional weight from the initial one. Such “yo-yo” diets disrupt the metabolism, are dangerous for the heart, and their repetition makes it increasingly difficult to lose weight.