There have been reports of YouTubers I watch getting sick after eating food in third world countries. However, these countries are also home to a large number of people who do not get sick from eating the same food. I think this suggests that the locals may have developed stronger immune systems. What do you think?
I find the OP’s question very intriguing and have kind of arrived at this same conclusion. My only tweak would be that they may, in fact, have more effective immune systems purely due to the fact that access to medicine or areas free of pathogens aren’t as common. Obviously, though, that would be compared to a person who exists in those same conditions but with access to good medical care which is a bit paradoxical.
EDIT: I made this more complicated for myself by thinking, further, that nutrition would also play a huge role in this