Gluten can induce zonulin release and open tight junctions, causing leaky gut, even in individuals without celiac disease.

“I do not think humans should mess with gluten, even if you are not formally celiac. ... I am not a fan of gluten for anyone. That is such an important point that I will repeat it. I am not a fan of gluten for any human. I believe there's a good amount of evidence that gluten, the lectin, and one of its components, gliadin, do induce the release of zonulin in intestinal epithelial cells in vitro and in vivo. Activation of the zonulin pathway by protein kinase C-mediated cytoskeleton reorganization and tight junction opening, aka leaky gut, leads to a rapid increase in intestinal permeability.”