Juice diets aren't really diets at all. They are fasts. Juice fasts typically claim to improve your metabolism, detoxify your body, and increase energy.

Juice fasts consist of vegetable and fruit juices, some diluted with distilled water. All foods are forbidden except the juices. The fast typically lasts for one to five days, although some juice proponents have had people on juice fasts for thirty days or more.

Short term juice fasts cause weight loss due to their low caloric intake. However, much of the weight loss is water weight which is quickly regained after ending the fast. Note that most people using juice fasts aren't seeking weight loss, but are looking for rejuvenation, internal cleansing, and other benefits.

The downside of long-term juice diets and fasts is that their lack of protein, fats, and other nutrients actually cause lethargy, weakness, and even mental confusion.

If you are planning to use a juice fast or juice diet, be sure to speak with your physician before beginning the program.