> Mental performance is harder to quantify, but I feel much sharper. A friend of mine frequently goes on crash diets and fasts and always reports that he feels

> Mental performance is harder to quantify, but I feel much sharper. A friend of mine frequently goes on crash diets and fasts and always reports that he feels sharper in the beginning. I'd guess (unscientifically) this is actually evidence that he is missing a few important nutrients.