You need to give your immune system practice. Whenever I go overseas, my first order of business is to eat the food and drink the water. I'm talking straight out of the tap or whatever ditch they drink it from. Food carts along the street, no worries.
It isn't pleasant at first and I've spent more than a fair share amount of time trapped in the little boys room, but I'm at the point now where I rarely get sick and eating foreign foods/water doesn't do much more than a day or so with an upset stomach, if that.
What actually messes me up? MSG and all the garbage "we" put in our "food" here.....I've cut out all the fake food from my diet about 1 1/2 ago and I've felt better ever since (I don't buy into the organic fad, I just want my food to be food and not a chemistry set).
And in some places, no problemo. I visited Latvia once and ate street vendor cuisine that didn’t seem to have anything more than the most rudimentary sanitary practices applied. Not even an upset stomach.
They warn that when you go to a restaurant ~ any restaurant ~ in India if you can't watch them cook the food you should leave immediately and go out into the streets to eat SAFE food.
All subtropical and tropical countries have this problem.