I've heard of doing fasting for 24+ hours for detox purposes (water only) but IF you should still be trying to balance your total calories(at first) so if you did one day off then the next day you should try to eat more. If you fast 16 hours you just make eat the amount you regulary eat in the condense window.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."