The assumption you're making is that your brain gets no calories when you have no food. Every kilogram of fat on your body is 9000 calories just sitting there. Most of us have at least 10 of em, or 90,000 calories.

While it's definitely true that some things slow down to conserve energy, it seems like the brain isn't one of em. There are moments* now I feel I'm thinking considerably clearer than usual. The world just feels unbelievably quiet. And things are getting done.

*I don't want to sell it as if it's all sunshine and rainbows. So far, getting to sleep has been hell, and the hunger pangs at times have been pretty insistent. While the hunger seems to have gone now, I have a general feeling of physical frailty, including lightheadedness when I stand up, and occasional light nausea.