how to stay focused

I’ve recently read an interview with Christian Bale in the GQ Magazine (don’t ask me why) and one thing that I found mostly interesting was his finding about hunger. Apparently, he had to lose a lot of weight for the shooting of “The Machinist” and that’s why he stopped eating. And after a while he realized how his brain was focused and suddenly clear.
Sounds nice, no? I think I’ll try it. It’s now the period of exams, the best time to try out such a thing.