I participate in IF and lift weights after work most days. I think it's mostly about timing. I'm usually done eating for the day around mid afternoon and feel fine working out after work. You don't need protein after you workout. You will be fine if you get enough protein throughout the day leading up to your workout.
I just finish a 21 day water fast yesterday - it’s the first time I’ve done it. My sleep was only slightly affected. Not because I was hungry, after 3 days your appetite more or less subsides. The only notable thing that happened as it relates to sleep is that I would only sleep for 5.5 hours and my body would wake up, not groggy or tired. Typically when I eat “normally” I get about 7 hours.
After a couple weeks I stopped thinking about eating until it was time to eat in the morning. Your body gets used to it. You just have to power through the adjustment period.
