[nwienert]

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.

[dasudasu]

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.

[Delk]

I'm pretty much that way, too.

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.