The concept of fasting and detoxification diets can have their place in general holistic health although for general fitness and weight loss it is a very poor method of fat loss. There are many types of fasts including juice fasting, tea fasting and water fasting. It is not that great of an idea for fat loss since your muscles literally jump off your body and run away when your body goes into starvation mode. Many life extensionists, however, use fasting to cleanse the body of toxins and others use fasting for meditative or holistic purposes. Whether or not detoxifying diets have any validity what-so-ever is a constant subject for debate between medical and holistic practitioners.  It is not my intention to enter that debate here or anywhere.  I have fasted a number of times to test the effects on fat and muscle and each time it was with negative results overall in the areas of fat loss and muscle retention. on the flip side, each occasion that I fasted or followed detoxifying diet programs, I felt quite energized and motivated by the experience.  So, while there may be many healthier and easier ways to lose fat than this, occasional detoxifying and fasting programs certainly seem to boost the motivation and energy of the individual not to mention the apparent increase in spiritual awareness that is so often found during fasting and detoxification programs.  As a caution though, fasting promotes protein catabolism and should be avoided for any prolonged or frequently repeated periods.  I am inclined to feel that a very basic food diet consisting of vegetables and fruits and plenty of water for a day or two will accomplish much the same "detoxing" effect without the wasting of proteins.