What I have been doing (mainly for fat loss purposes) is circa 44 hour fasts three times a week, i.e. Mon/Wed/Fri. I will train the remaining 4 days.
Typically, I will ‘break’ the fast late afternoon/early evening using peri-WO shakes and then eat low carb a few hours later (at night).
I have found this style of alternate day fasting pretty easy to maintain. Social/family constraints can be the biggest challenge but I am fortunate here, so it fits my lifestyle.
As has been pointed out by the likes of CT, the downside of such diets is a propensity to overproduce cortisol. This is even more of a factor if you are working out late. Similarly, late eating can mess up your circadian rythmns. So far, it’s working for me but, all going well, I expect diminishing returns over time.
The other angle worth highlighting is the difference between, what I would term a strict, or true, fact and a dirty fast. The former should be water and maybe some electrolytes. The latter includes teas, coffee, maybe some sweetners, flavoured waters, gum, etc. The former is, no doubt, optimum for health and maximum autophagy; while the latter can get you through patches where you’re felling a bit sorry for yourself. While I have done both, I now tend towards the dirty fast.