i began to take dextrose whenever i need an intellectual boost and it is VERY effective. (20-30 g, sometimes more)
i used to take fruits but dextrose get to your brain much faster. And because i loved fruits i used to take too much of it. Dextrose is also obviously much cheaper.
I think i get this effect because i take a lot of nootropics that increase brain metabolism in the brain.
ps: i don't get fat