My wife has long figured she has a gluten sensitivity. However, many doctors and researchers believe there is no mechanism for that and that it isn't really gluten at all, but something else.

We have found that it isn't so much the quantity of gluten, but the quality of the product. For example, a piece of cheap, white bread has bad effects, but a piece of whole grain, organic bread or sourdough is usually fine. This could be fodmaps, but we have tried cutting those without much effect.

Right now, our working theory is contaminants and mimic weeds that make their way into wheat and other cheaper products where as the supply is a bit more controlled in the higher end and organic products. But we are still mostly befuddled.

There is the glyphosate hypothesis that seems to fit your situation: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3945755/

Interesting. For my wife it certainly is gluten and for a long time, cheap white bread was easier on her belly than whole grain bread.