In addition, I think the magnitude of opioid effect
> is not nearly strong enough to explain the magnitude of the
> dietary shift.  We're not talking about opium poppies or coca
> leaves here.

Do some more research.  Both glutens and caseins are able to cross the
blood-brain barrier due to their remarkable similarity with endogenously
produced brain chemicals, and once there they can and do lock into opiod
receptors.

Andrew