Not all flour or sugar are made equal. I wonder what happens if you try flour or sugar from places where some questionable herbicides are banned.
It's really very easy to buy in to the dominant social narrative as an explanation for one of the many undiagnosable health incidents we experience in a lifetime, and the placebo effect confirms whatever is socially helpful.
Most of these social changes now originate or become big from the US first because it dominates international media.