Yup, I will second the elimination diet. Starting with a fruit fast and gradually building a set of safe foods I could fall back on when sick. For me this is:

* apples & pears
* omelettes with carrot, egg, tofu
* milkshake made from tofu, honey, and cocoa/carob

what I can eat on the diet (click here) -- my blog -- contact me (PM is broken)
"Some men, in truth, live that they may eat, as the irrational creatures, 'whose life is their belly, and nothing else.' But the Instructor enjoins us to eat that we may live." -- Clement of Alexandria (about 200 AD)