Seems like a mycotoxins problem to me. You should google for sure. Basically mycotoxins are produced by food fungi (bacteria).
Wheat, soy, milk etc are the worst.
He can try this diet. It's called the no grain diet. No fruits either, he can have unprocessed meats except pork and no seafood or eggs. He can eat broccoli, celery and cauliflower. Only low carb vegetables. A lot of water is good and drinking green tea (not the ones from the grocery stores).
Probably best to do this for 60 days he can go on it for 30 days. Never eat processed foods or any wheat products because they are highest to digest and contains the most mycotoxins. Rice is the healthiest grain so if he needs to eat grain during the diet he can do so and watch and see. Limit to 3 serving a day at the most.
Also when cooking meat don't heat above 200f because it turns the chemcials in the meat into toxins. You can microwave meat first then bake it or boil it. No spices or salt by the way.
You can try moderate amounts of coconut oil and/or virgin olive oil, these oils are antioxidants that kills bacteria.
Anyways I suggest you try that.
Just remember foods can heal, I am curing myself from severe bacterial ucler without any meds!
Good luck