From "The Great Law" by Hilton Hotema,we find a description of Fitzsimmons frugal diet and,from memeory here, I am quite certain it was a head of cabbage,raw, and 5-10 brasil nuts daily. That was pretty much it. Basically the book by Hotema builds a case for understanding that all we need comes from the air, but of course 99% of us do not have the additional 100 glands that Breatharians have, so we cannot duplicate this easily.
The Great Law is a fantastic book by the way and will change the way you think about a great many things. Highly reccommended.