There are so many IBS diets out there that it can be confusing - after having had IBS since 1983, I was down to crackers and water at one point because everything seemed to put me into severe pain and attacks. Common sense would say not to eat something that would already aggrivate his system, but we know from experience that sometimes if the person eats the 'trigger' food unknowingly, there are no problems.Take a peek at my links below- I no longer follow an IBS diet, and there can be a way forward for your son. In the meantime, he could probably have a modified pizza, keep it as bland as possible, and pasta usually is pretty safe - but some people have tomato as a trigger, others do not, so as mentioned, it is not a one-size fits all thing. And to add to the complications, many IBS patients can have one food one day with no problem, and another day it may be the opposite. If I can be of any help, please let me know - I speak (for free) with many IBS patients to share what has helped me after all else failed.All the best, and do not give up hope for your son!