If you are 300 lbs, you'll likely lose an average of 1-2 lbs per day during the cleanse. However, that's not necessarily permanent. How you come off the cleanse is very important and if done wrong can not only be dangerous but you'll likely gain that back plus more. It will require a much larger dietary and lifestyle change after the cleanse to maintain your weight loss. Have you ever done a fast before and did you prepare for this one? I recommend doing a pre-cleanse diet of raw fruits and vegetables and fresh juices before beginning your MC. This will jump start your weight loss and detox and help you ease into the Master-Cleanse better.