I know some claim to exist, I haven't been personally convinced yet but hey who knows. I've read tidbits like a girl who stopped eating at 12 years old and by 15 parts of her digestive system had closed over and they said some of her digestive organs were 'digesting' the air she breathed and creating any nutrients they might otherwise have been deficient in. Again my empty head can't remember which fasting or other type book I read it in unfortunately, if I find it I might be able to look up the reference.
Linda Goodman also fasted a fair bit and spoke about Breatharianism in her book Star Signs quite extensively. Again very interesting but as I recall it was mostly second hand information she was discussing.