I’ve never done the long term fasts, but my anecdotal experience also confirms this - I definitely have significantly less mental clarity on any type of fast I’ve done, to the point where it definitely affects my productivity even by end of day 1.
Myself as well. You just hit low blood sugar. Technically not fasting, but I have an appetite so weak I can skip meals easily and will do so if I don’t pay attention. Eventually I just feel very lethargic and enter what I can only conceive of as “starvation” or “energy conservation” mode. It’s not pleasant. I also have trouble with muscular mass being the first thing to go.
I think I also just become more irritable if it's been too long since the last time I ate. It definitely doesn't seem to improve mental acuity for me, and any kind of physical activity is just going to feel worse. I've never tried any kind of a formal fast, though, so I don't know if there's something to planned schedules that makes it different.
I can kind of see how I might, under some circumstances, enter some kind of a state of quicker thinking after fasting, but I think it would be something similar to sleep deprivation, where you get perhaps a bit "hyper". That's not really a state I necessarily strive for either.
I've also never been overweight, and have always had more trouble gaining weight than getting rid of it. I wonder if that has something to do with it. I suppose the metabolism might be different if you've got some fat stores vs. if you're rather low-fat.
I can understand how fasting could e.g. have differential effects on cancer cells and thus be useful in specific circumstances. I also understand that people have rather different reactions, so I don't doubt that some people achieve some kind of a state that feels good or useful by fasting. But I don't really understand the hype, or calling it a panacea.
