Oh, of course! It's not a very common diet, but a handful of Psychic and Ghost types eat things like dreams and emotions.

I don't really understand the specifics myself, I'm not a professor or anything like that--but from what I've seen, it seems like it's basically a kind of energy absorption? We have to physically break down the chemicals in food to convert it into energy. They must be able to perceive and manipulate dreams, and break them down into the psychic energy that created them.

But since dreams aren't tangible to begin with, it's probably a lot less work than digesting food, don't you think?