There are many ways to drive a person mad. You can leave them in solitude, keep them from their sleep or even overload their senses. But the oldest and most certain way to spark that madness inside a person is to starve them.
Hunger will eat a person from the inside out. When your body hungers one of the first things to go is the mind. You'd do anything to fill that hole in your gut. You'd eat dirt, bugs, bushes...people. When you have that crawling, gnawing hunger inside you blood becomes ambrosia and the flesh is the sweetest treat.
But it changes you in a most primal way. Once you've tasted that succulent flesh your strength soars to new heights, you grow well past your limits and...your hunger comes back with a vengeance. It's a never ending cycle, you have to eat other people in order to stave off the hunger only for it to come back stronger.
But I would be lying if I said you don't come to relish it.