There's a lot to be said for self-experimentation. One of my friends has found that his digestive system "shuts down" (constipation, lack of satiation, possibly additional symptoms I've forgotten) if he doesn't eat wheat. This trait runs in his family. I haven't heard of anyone else having it.
One's ancestry and long-lived populations give clues about what to experiment with, though.
That's fascinating. Do you know what he tried to replace it with?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.