I've heard people who people who travel from a modern city to a 3rd world country, they often get diarrhea due to not getting used to the food. But then, what about the other way around?
How about 2 people travel to a new country together, can 1 get diarrhea and the other does not? Or, where they both get diarrhea, but 1 quickly gets immune to the food, the other does not? And let's take out consideration such as lactose intolerance, diabetes, food allergies, etc. Thanks.