I actually revised my estimated fat loss to 5.5 pounds from 4-4.5. First i will say that i acknowledge that this is not a perfect system and that there is a lot of estimating involved.. I estimate how many calories my body is likely burning (bmr/basal metabolic rate) and that about 90% of those calories are coming from stored fat... and take into the account that the metabolism at the start of the fast is likely to be about 25% higher than it is today.
If my average bmr over these past 12 days out of the 14 has been 2000, that would mean 1800 calories per day have been coming from stored fat which is 1/2 pound per day for the 12 days out of 14 (as the first 2 days were primarily carb burning days). This would put me at 6 pounds of fat... However i believe my average bmr with a metabolism slowing to preserve my reserves has been slightly less than 2000, my best guess being about 1900, so that puts me at about 5.5 pounds of fat.
Another aspect of my confidence is based on lots of post fast experiences watching my body add a pound per day for 15 or 20 days when i was eating extremely lightly, far below the number of calories it would take to add that much fat as it would take 3600 excess calories per day to accomplish this and i was eating at or below my estimated bmr which would equate to zero fat gain.
And how we loose mostly water if we drink water all the time?
The simple truth of it is that most of us when fasting eliminate a lot more water than we take in... through urine, sweat and evaporation. We lose a lot of sodium in a fast, especially in the first week and sodium which holds water takes this water with it. I was down 16.5 pounds in the first 7 days and lost only 6 pounds over the following 7 days. These first 7 days were days my body was eliminating a lot of sodium (and taking a lot of water with it). When we begin to eat again and regain our normal sodium levels through the natural sodium in vegetables and fruits, we also regain our normal water levels.