Trying to put off fats can also be risky. This trouble is more with excessive diets that promise to take off quite a few weight very quickly. These diets can encourage loss of muscle rather than fat. They also boom the risk of heart ailment, a slowed metabolism, and other fitness issues. Liquid diets, intense calorie deprivation, and fad diets that put off complete classes of meals are the most dangerous; but any kind of diet can be hazardous for your fitness if you time and again lose and advantage weight, or "yo-yo."