Whats a fad diet --like only juice and water?

Unreasonable. A fad diet is any eating plan this is unreasonable and, most importantly, cannot be sustained long term. These diets tend to fail because when you back to "normal food" all the weight you lost comes back too. In addition, if you have any health concerns, a fad diet may be very dangerous to your health. Check the "dash" eating plan - it's safe and it works, and no one is selling it.
Diets. Fad diets are marketing ploys to promote a concept that has more to do with making money than with a well-balanced diet that promotes long-term compliance conducive with a healthy lifestyle. Many of these diets are also low calorie diets. A low calorie diet is a diet that provides extremely low calories in order to produce significant weight loss. They can be unbalanced and cause problems.