Have you been onto the Fast 5 website and downloaded the free ebook? There might be an answer to your question in that. Most of the people i've spoken to either haven't counted calories during the 5 hours and just tried to eat healthy. Or they have stuck to a calorie limit. The lowest people who have counted have gone is 1200 as its generally thought not to be a good idea to go below that per day. I guess you could experiment a bit. Been a while since i last read the ebook but i do remember it said its quite common not to lose in the first 3 weeks so if that happens don't panic.