I averaged 1.3 lbs/day for the entire length of my 60 day fast, and the first two weeks were much higher weight loss than usual. I can see 18kg in 18 days depending on what size you are. Of course 2-4kg will be water weight and another 2-4kg will just be stuff that lives in your gut, which is to say you'll gain it right back when you start eating again.
I just rolled into day four of a fast and the delta from two days ago is 3.72 kg.
Most of the weight you lose in the first 3 to 5 days of a fast isn't fat, its stuff in your gut and losing water as you draw down your glycogen stores.
