[samatman]

Ketosis isn't a shortcut, it's a critical part of the human organism.

The brain has to run on something, and we store very little glycogen. It wasn't uncommon in the ancestral environment for food to be entirely unavailable, or for the only calories to be in the form of meat, which itself has little glycogen.

So there's a secondary pathway to account for those conditions. A hand-waving argument could be made that in circumstances where there are no calories, it is the most important time for the brain to function well. Glucose is the cheapest, metabolically, that doesn't automatically mean that it's the best.

The reaction someone has to a fast, or to a diet which induces ketosis, is fairly personal. I don't think there are broad sweeping conclusions we can draw here.

My n=1 is that after two days of a fast, I feel pretty sharp. Electrolytes are indeed essential to this; in this context salt is far and away the most important, for whatever reason. I would expect the YMMV factor to dominate though.