This forum deals with water only fasting, but I'll be happy to give you some pointers. Most people, especially those who carry a lot of extra weight are too toxic to safely do a long fast or cleanse. My advice to to start slowly and build up to a longer fast or cleanse. Here are a few tips:
make sure you are hydrated, drink plenty of pure water, but never chug it down; sip water slowly throughout the day
include lots of raw fruits and veggies in your diet, these will gently begin the detoxification process
try fasting one day a week, after four to six weeks of once a week fasting try for three days a month of water only. While The Master Cleanse is very good, you can usually get the same results with water only fasting in three days; just make sure your diet is clean
Try some Liver Flushing and colon cleansing between fasts, this will help detox and improve digestion. This is crucial to permanent weight loss.
I've gotta get to work now. Good Luck, I will answer any questions if you send me a message.