Nice work on the losses so far! I also work out on fast days. When I do, I make sure to excercise first thing in the morning so afterwards I can have a thick protein shake consisting of whey protein, spinach and greek yogurt (about 275 calories). I then fast a full 12 hours and have another 300 calorie meal in the evening time around 7:30pm. So far this has worked great for me. Hope this helps!