Here's an anecdote: The first time I did a longer fast (72 hours) I felt low-energy, as you describe. Then I ate a single large meal and did another long fast

Here's an anecdote: The first time I did a longer fast (72 hours) I felt low-energy, as you describe. Then I ate a single large meal and did another long fast; that felt quite good for the duration of that fast... so I did that for a month, more or less, and lost a lot of body fay (I'm 6'4" and I went from 225 to 200). And then I was being pretty healthy for 8 months before going back to occasional drinking, but I still don't do sweets other than fruit. I mostly eat a single meal in the middle of the day (though I make a lot of compromises due to being around other humans) and I don't usually find myself hungry in a way that is intrusive on my thoughts. However, I did start rock climbing in a gym and I upped my caloric intake and would eat a small meal afterwards. I did another series of fasts this spring to bring my weight down to 175, and it's stayed there. And then I did a short series of longer fasts this fall, and didn't feel low-energy during them.