I'm not sure its the grain itself, maybe more the processes from the last 50 years or so.
gluten is just a protein, problem is that folks become allergic to it so you get celiacs or gluten sensitive, though most people that claim gluten sensitivity are full of **** and just following a fad.
Anyway, white enriched floor, starts life as just good ole grass seed, then its micro ground, bleached with chlorine that leaches all the natural vitamins and several minerals, so they replace that with synthetic versions, kinda ****** up really since if you just let floor sit for a while you get a fairly white floor without loosing the good stuff or using scetchy chemicals on it. Buy you don't get wonder bread out of naturally bleached floor...
the other issue is that wheat is really easy to grow, so its cheap, especially with modern fertilizers, so it gets used in damned near everything, corn is the other easy grain, possibly easier, so it too ends up in everything.
So when a person is exposed to something constantly over long periods of time you start to have negative reactions to it, like sitting in the pool for too long, yer skin gets soft, only a little different. for some folks it becomes an allergic reaction, or in the case of celiacs the erosion of the guts.
Anyway, sucks to be Bob...