And it’s not just genetics that are local. Gut microbes matter a ton for how you digest food, and it’s determined by where you live and what you eat. The immune system matters too, this is why travelers diarrhea is a thing. And that is also diet dependent: one who doesn’t regularly eat seafood will easily catch viral gastrointestinal infections from eating clams for example.
So there is no single global “healthy diet” for everyone, you got to start from what’s available locally and what your people eat, and tweak that as necessary.