They lose weight yes, but they lose muscle and water as well..and afterward, its possible to gain a lot more back plus what you lost. Its not a soloution to permanent weight loss. Its usually used in a more spiritual sense.. Also, have you ever attempted to go that long without food? Ive gone 23 days without food..just water.. i attempted this water fasting thing..and it was very very difficult, and under those circumstances, the ability to keep your normal routine is very hard. You are very fatigued, very irritable, you crave everything, you feel sick, you have a hard time going to the bathroom, you feel dizzy and lightheaded and you feel very tired..Its not the type of lifestyle you want .. and as i said, that weight you lose off the scale, is water and muscle as well as fat..and the ability to maintain that loss after that fast, is really really difficult..cause everything you eat after that fast, your body holds onto..If your going to consider some kind of fast, i suggest you try something like the Master Cleanse. Type it into google...you will get the downlow on it and how to do it..its much more tolerable by the body..