[wholinator2]

Genuinely asking, do we? Like, we might understand the mechanism but do we actually understand the cause, the "why" behind the mechanism? It was my understanding that there's practically infinite variety in which foods cause symptoms for different people, and that the specifics of each were still largely unknown

[spondylosaurus]

Well, for one, foods aren't the only thing that affect symptoms. And a lot of food issues are related to (1) which parts of your GI tract are affected and (2) what's wrong with them. People with strictures usually need to eat low-fiber diets, for example, but people without structures can actually benefit from some fiber.

The "why" is a little less clear, but it's likely a mix of genetic factors and environmental/infectious triggers. Plus good old-fashioned stress :)