One confounder with gluten is that every single type of bread except well produced sourdough is high fodmap. And fodmaps can produce a lot of digestive symptoms.
Celiac is more well known than fodmap issues, and you'd have apparent causality. Eat bread, feel bad. Don't eat bread, feel better.
But not perfect, as many other foods are high fodmap.
Anyway it turns out those with giardisis are sensitive to high fodmap foods so perhaps that could explain it. (Surprisingly also sensitive to low fodmap foods)
Celiac is more well known than fodmap issues, and you'd have apparent causality. Eat bread, feel bad. Don't eat bread, feel better.
But not perfect, as many other foods are high fodmap.
Anyway it turns out those with giardisis are sensitive to high fodmap foods so perhaps that could explain it. (Surprisingly also sensitive to low fodmap foods)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4653841/