Ummm, that is a very broad and vague question. We can't answer where he can get good treatment unless we know what he has already tried. As for diet, he needs to eat very bland foods (no spices) and foods low in fiber (avoid fruits, veggies, and nuts). He needs to drink TONS of fluids. When having diarrhea, you should drink double the amount that is coming out of you.
"For this thing I besought the Lord thrice that it depart from me. He said, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities; I take pleasure in infirmities, reproaches, necessities, persecutions, distresses, for when I am weak, then am I strong" 2 Cor