You're right though, the engineering that goes into our bodily machines is mind boggling.
https://www.implantica.com/im-refluxstop/patients/gastrointe...
Who knows?
All I know is that it's different for everyone and for lots and lots of people, eating totally normal things is what causes or contributes to lots of bad symptoms misattributed to some disease or disorder. More often than not it's not you, it's the utter garbage food that our society has standardized upon. Just because it's common to eat a sandwich, or pasta, or a bowl of cereal or granola, or a bagel doesn't mean that human evolution has caught up with it yet.
I live on espresso/tea, heavy cream, protein/nutrition shakes, zero-cal flavor syrups, and grilled beef. It's sort of crazy how much healthier I am eating this than if I ate, say, even healthy sandwiches. My body just seems to dig being primarily a carnivore. If I personally liked vegetables and leafy greens more I would probably do vegan keto, as I don't like how unsustainable western meat production is, but I simply can't get into the idea of leafs as food.