I've dabbled in fasting and found my ability to do it comfortably varies a ton day-to-day. Some days I'm craving food by noon and/or am very tired and practically can't think at all by 3PM (this is pretty bad on work days, obviously, but not really great on any day). Other days I can go from wake-up to lie-down without a single bite of food, and hardly notice a thing. I can't tell in advance which it's going to be, so rather than sticking hard to a fasting schedule, when I'm in the mood to do it I'll pick days to try, and if at some point it becomes clear I'm gonna wreck my whole day if I persist, I bail and eat a meal. Ends up being about 50/50, days that work out and days that don't, if I try a couple days per week.

Sometimes I can approach 48 hours before I start to feel bad, other times I can't even make it one day before I'm a mess and can hardly function. I'm sure the difference has to do with blood sugar timing and/or what I ate the day before or something.