"(Your gut fauna also adapts over time, which is why the locals don't get sick so often)."

Heh, this isn't actually true, or not meaningfully so. Where I lived, it was recognized that getting sick regularly was a fact of life. The place I lived had almost no tourism, so people getting sick were, in fact, just getting sick from an essentially unregulated food market.

But hey, freeeeee market, right?