Definitely it’s not obvious that gluten specifically would be the cause, but seemingly obvious to test specialized diets?
So I guess I’m surprised people didn’t discover “avoid wheat” a lot sooner even if it took until the late 20th century to actually understand the mechanism.
Celiac disease is far more severe than what's now called "gluten intolerance". But maybe they're related.
I get that "Celiac disease results from genetic abnormal immune response to gluten."[0] I'm not sure what that means, in detail. Perhaps there's a particular allele of one of the immunoglobulin genes. But whatever it is, perhaps other alleles cause "gluten intolerance" of varying severity.
Combined with this with the role bread used to play. It was a massive part of diets until relatively recently when we turned bread bland and relatively nutrician free with mass production techniques.