For good usable information on intermittent fasting I’d check out Gin Stephens - she has a couple of useful books (“Fast, Feast, Repeat” and “Delay, Don’t Deny”) and a lot of podcasts. Basically clean fasting is only having black tea or coffee or water in your fasting window. No milk or sugar, nothing flavoured, basically trying to avoid anything that might spike insulin. I find this really the best way as although it sounds harder you don’t get hunger pangs after the first few days of acclimatising. I go from 7pm-12 noon the next day as a rule - I’m not especially strict now although I was at the beginning and often did only 3 or 4 hour eating window - I work out fasted every morning and just have a black coffee afterwards, and I get through until lunch just fine. I do eat a fairly hearty lunch but I’m not fainting with hunger or anything, I’m just hungry enough to really enjoy my food, and not count what I’m eating. Just a good amount of nutritious whole foods.
Interestly in the last few weeks when I was finishing up Epic 3 I was very hungry in the afternoon and craving carbs and sweets. This week starting Iron that’s disappeared and I’m not that hungry at all. So I do think sometimes you just have to listen to your body. I needed those carbs obviously!