There are 2 main items that can upset your digestive system, one is the water, and the other one is the ingredient that is used to cook.
Different geological areas will have varying amounts of minerals in the water, and ower systems are used to a given pocentage of those minerals, some intestinal systems will react faster to adapting and others will rebel, in order to avoid this drink mineral water or beer, morning coffee or tea will not affect the system as much, if you are conserened of getting a nasty bug wash and rinse your teeth with mineral water in a clean and washed glass.
The other item is the cooking oil or grease that is used regionally, some digestive systems will react slow and others fast to the change in fat or oils in whitch the food is cooked, oil used too many times and only strained for burnt or uncooked particles becomes a source of intestinal ailments, and some fancy restaurants tend to do this more often, avoid fatty foods and or foods that are cooked in oils Eg. french fries Etc. Also avoid salads or uncooked foods until you get to know the restaurant better or the area.
Try to eat the meats well done (bien cosida) rather than medium rare (termino medio) quickly pan fred or better cooked in an open flame if possible.
I have always drank mineral water in my travells or beer, and I carry a bolle cap opener on my key chain and always tell the waiter that "I will open the bottle" and that I will not accept the bottle if it comes open, I have refused beer bottles that were opened at the bar and brought to the table, you never know if they droped something in it to get you really happy, one thing that I do not do at all is have cocktails or hard liquor from the bar, only if they bring a new bottle of Tequila or Mezcal, call me paranoid in that sence, I have watched too many people get really silly and stupid with one drink, including my sister and I know she could belt down at least 3 beers, we were at a disco in Acapulco my beer was closed every one elses came open, guess who drove back to the hotel.
If Moctezumas revenge does not start to clear by the second day, that will indicate an intestinal infection and you need to take some medication, that is not a digestive tract uppset provided you took copious quantities of mineral water, dehydration worsens the situationñ in both cases.
I have travelled from Seattle to Washington DC and down to Panama and from Norway to Portugal to Greece and only got very sick in Tehucan Puebla, had rough ride down the Shenandoah to Washington DC, hot day and drank cold sider on the way down the mountain, good laxative that sider cleaned the plumbing right out.
Visiting and travelling in Mexico is no different than visiting and travelling any where in the world, taking some small precautions will ensure that you enjoy the the travel.
navegator