Those medications don't just mask the symptoms. They are capable of actually healing the underlying inflammation. That doesn't happen in everybody who takes them, but it does happen in many patients. Usually when symptoms improve so dramatically, that's a good indication that the underlying inflammation is also improving. But that's not *always* the case. Only more tests can determine for sure.
As for diet, he should eat what he tolerates, with a bit of an emphasis on 'healthy eating.' That means fruits, veggies, whole grains (if grains are eaten), chicken, fish, lean meats, low fat dairy, nuts, whatever. But he can also be a normal teenager and eat pizza, ice cream, burgers, etc, from time to time. Just make sure that pizza and burgers aren't ALL that he eats.
