I typed up a short intro on why gluten is bad for you and what it’s doing to peoples’ bodies.
Zonulin is a protein that modulates the permeability of tight junctions between cells in the digestive tract.
(See tight junction below.) Tight junctions stop macromolecules from leaking into your body from your gut. They’re supposed to be pretty much impermeable to macromolecules to avoid triggering the immune system. Zonulin lets some macromolecules through when it’s activated.) Nutrients from the gut are mainly supposed to get to our blood by going through receptors in the cell wall, not by going between cells.
Gliadin (half of the protein that makes up gluten) activates Zonulin. Activating Zonulin makes the tight junctions more permeable than they should be and allows macromolecules to leak through, activating your immune system. This happens to everybody who eats it, but people with celiac end up with much more damage. Regardless of who you are, it’s poisoning your body.
The reason this is a problem is because having an immune system that’s attacking something, leads to generalized inflammation (through other cell processes). This can harm other tissues as well, and tissues surrounding what your immune system is attacking. It’s not just the gut, it’s joints, skin, brain, nerves, organs. The least it does is make you tired, depressed, and weaker. The most it does to you is makes you batshit crazy.