What about muscle loss? I haven't tried fasting because I don't want to lose muscle mass. Maybe my concern is unfounded?
I know that they do IF, but do we have examples of bodybuilders that do 3+ day regular fasts? I'm not aware of any. IF can simply be a neat way to calorically reduce, but legitimate multi-day fasting is another beast entirely.
Regarding the fasting time, I think there's a big difference between the IF you are doing and eg the multi-day fasts people here are talking about. They don't sound helpful for strength sports.
Longer fasts are something different entirely. They have their place, but are more of an event that must be planned. Personally, I like things I can do for life and turn into habits. I don't see how I could make 3-7 day fasts a habit.
Oh, and I'm not the person you asked, but my best DL was conventional 525lb weighing 199 :)
I would agree that multi-day fasts would not be good for strength sports. There doesn't seem to be a authoritative source but LeanGains states you won't lose muscle if you're fasting less than 24 hours. (https://leangains.com/top-ten-fasting-myths-debunked-major-u...)
It looks like you can lost a fair amount of muscle mass, and that you lose the most muscle mass early, so 1 21 day fast would be better for you than 3 7 day.