Just add, if you DO do a fast, don't go cold turkey, you have to ease yourself into it from what I've read. The longest fast I did was 2 days, and honestly, after the first day you don't feel that hungry (well it comes and goes in waves).
The most most most important thing if you're going to fast for any length of time is to DRINK LOTS OF WATER (or natural juice if you're doing a juice fast). The entire point of a "proper" fast (not anorexia, that is a disease) is to cleanse the body out, but it needs lots of water to do so (and water can help make you feel a little fuller). Don't drink too much though, anything more than 4L a day (about 135oz) will cause an electrolyte imbalance - which can cause nervous system malfunctions that are similar in symptoms to having multiple sclerosis (seizures, "mixed signals", etc). Anywhere from 60-120 oz a day (which is 8-16 glasses a day) is fine.
One thing I also want to stress is to not do fasting just for weightloss. Weightloss will happen of course, but that's a happy side effect, not the goal. Also, when finishing a fast, you want to ease back out of it, because as mentioned, after that long without food, your body will cling to every calorie you give it. So start slow with broth-based soups and natural juices, and work your way up from there until you're back at a healthy calorie intake.
