Kate Osborne
Peter Osborne

His problem is not your problem.  People are different.  If he really wants to understand, have him watch the first Glutenology video.  It is not a simple one liner answer that can be given.  Expecially if he is already resistant to hearing the truth.  Bottom line:  different people react more or less violently to allergies (delayed or acute) and intolerances. 

All the best,

Dr. O