In no way is fasting healthy for you if you rely on having energy, focus, or any ability to function as an independent adult while fasting for more than a day or so at most.
I've fasted for up to 5 days before, and I felt just fine - especially on days 4 and 5, I actually feel like I have more mental clarity and drive than usual.
I guess this is always my question of anyone who has a positive experience with fasts. Personally, I have been at the mid-upper range of healthy bf%/weight for years and exercise frequently (running 30+ minutes 7 days a week for a few years, cycling 60+ minutes 2-3 a week this year) and find much shorter fasts (say, 20h) excruciating and completely draining mentally and physically. And I'm not at 7% body fat like that other guy. Lowest I got was maybe 14% while I was running daily; while I'm up to 18%ish now, fasting hasn't gotten any easier.
(Even if I skipped exercising, just the mental effects made my mood significantly worse by the end of the day, which makes it harder to work effectively in a collaborative environment.)
What's your non-fasting diet like? Fasting is the quickest way to get into ketosis. If you're used to eating a carb-heavy diet, the switch into ketosis can be brutal. So if you either ease off carbs leading up to the fast, or just all the time, it'll be easier.
The other thing is electrolytes. Your body doesn't store them, so you (IMO) have to supplement. If you start to feel like crap, have 1tsp of salt in about 1L of water and see if it fixes it. I also supplement with magnesium and occasionally potassium.
I'm sure Dorsey isn't the only high profile/ functioning CEO who does multi day fasts each week.
"Not only are we deeply wired to function for long periods of time without food"
So the body doesn't collapse after x number of hours without fuel. Your body also has the ability to generate its own heat when it's cold. Does that mean that it's desirable or ideal that we deliberately use these abilities? Does it mean that there is no harm or risk in doing so? I'm not saying that there is or isn't; I don't know.
"but when you haven't eaten in a while your mind becomes focused and alert"
This is sort of like the focus that you get when you're being chased by a wild animal or falling out of a tree. I don't know that seeking focus from sources like this is a great idea, but YMMV.
"since your body thinks it needs to find or hunt food."
So maybe your body is telling you that fasting isn't such a good idea?
"I'm sure Dorsey isn't the only high profile/ functioning CEO who does multi day fasts each week."
I don't do multi-day fasts and I've lived for years longer than Dorsey.
The evolutionary angle isn't the reason why I believe fasting is a good idea - it's just a rebuttle to "there's no way you function well while fasting"... of course you can, it was likely the MO for millions of years of modern human evolution (or 100+ M years for mammals). It's as natural to fast as it is to fornicate.
Rather, my reasons for fasting come from the scientific literature, centered around autophagy, insulin control, sirtuin activation, visceral (organ) fat depletion, and troves of clear lab test results of benefits (albeit most on non human mammals).
Based on many comments here I think folks just haven't caught up with the longevity research of the last 3-4 years.