Crash diets have the ultimate appeal: lose lots of weight in a short time and without much effort. However, these diets come with some small print that is easy to miss. Lose weight too quickly and you're likely to gain it back. Diets that cause rapid weight loss are also likely to be unhealthy. Picking the wrong diet can put your health at risk.*
Diets that completely eliminate a food group can also be dangerous. To stay healthy, your body needs carbohydrates, proteins and fats. Drastically reduce one of those groups and you'll be missing out in a number of nutrients. For example, some vitamins are fat soluble. If you eliminate fats or take fat blockers like U.S. Food and Drug Administration-approved diet pill Alli, your body might not be able to absorb certain vitamins, according to Drugs.com.*