Gluten is not an ingredient added to bread, it is an integral component of the flour used to make bread.
I know that. My point is that the only description of the bread used in the Last Supper, upon which the Eucharist is based, is that it was unleavened because the dinner happened during the Passover. We assume it had gluten because bread could not be made without it at the time, but I'm not sure it was even known at the time and if the bread had been made with any sort of gluten-free grain, I don't think it would have been any less valid.
If a church parishioner has to choose between getting sick from a communion wafer and being denied communion all over an arbitrary insistence on what kind of grain is in the wafer, I don't think that fits in with what Christianity is all about.