I experimented at the start of the year and didn't experience any drop in performance - office or gym - with water fasts less than 24 hours.
Fasting between 24-72 hours, though, really affected my sleep and made me feel weaker during workouts (though it didn't really affect me mentally). Curious to see if others experienced the same.
Can't comment on longer fasts as I didn't exceed 72 hours (though I did read many reports of it actually getting easier after that point in time).
Currently doing IF (very rough 20/4) which is working pretty well.
Honestly it varies massively - I play it by ear, as it's normally interrupted by going out to dinner with friends or dates.
I fast once every 10 days minimum (arbitrary number, but it keeps me disciplined). If I've had a few weeks of excess (lots of drinking and greasy takeaways) I might do 3-4 days. At least 2-3 times a year I like to do a 6-8 day fast. I've done this for the past 4 years and I've felt remarkably better for it, with the most noticeable thing being reduction in scar tissue (from surgery) and inflammation symptoms.
In terms of how it makes me feel while fasting, it depends on the day. A one day fasts tends to make me just feel hungry around meal times, assumedly because I'm still largely running on the glycogen in my muscles. I used to find day 2 pretty rough, as I'm guessing that's how long it would take for the process of ketosis to start in me. As your body adapts to frequent fasting though it becomes plain sailing though. I'll often arrange my fast to coincide with a large stint of work, as I feel my mental clarity is much higher - akin to taking Modafinil if you've ever tried it. Hunger isn't an issue for me at all once I'm in a state of ketosis.
I highly recommend doing an extended fast at some point. If anything it allows you to become much more satiated by smaller portions, and it eliminated any sugar cravings I used to have.
I experimented at the start of the year and didn't experience any drop in performance - office or gym - with water fasts less than 24 hours.
Fasting between 24-72 hours, though, really affected my sleep and made me feel weaker during workouts (though it didn't really affect me mentally). Curious to see if others experienced the same.
Can't comment on longer fasts as I didn't exceed 72 hours (though I did read many reports of it actually getting easier after that point in time).
Currently doing IF (very rough 20/4) which is working pretty well.