So, according to Kresser (and he cites Dr. Kenneth Fine of Entero Lab), a lot of people are gluten intolerant--up to 30% of the population. Most of these people are unaware that they're gluten intolerant because their intolerance does not present as gastrointestinal symptoms. So they could eat gluten and feel "fine." It's just that, after years and decades of consuming gluten, they eventually develop an autoimmune disorder when they're older. The effect of things like HFCS, gluten, and PUFAs are cumulative and chronic so most people are not going to have a sudden, acute reaction to consuming these things. But years and decades of consumption eventually produces problems.
The Gluten-Thyroid Connection