Excuse if someone's asked this before and I missed it, but:
Paul, it sounds like your friend has been ill when trying GMO foods and fine with organic foods. I don't think you mentioned whether he had tested non-organic, non-GMO foods? There are a lot of things that fit into this category, at least where I shop. If these foods also bother your friend's digestion, it would be reasonable to conclude that he is intolerant to one or more additives, herbicides, or pesticides; rather than the results of GM.