For the traveller from America to China, perhaps little will be more disconcerting than the stomach's ability to adjust to the new diet. It's not something most will consider before travelling. Nonetheless, I can report that it took my stomach about two weeks to make the transition from my standard diet (which is probably not as healthy as it could be given that I don't eat meat (fish being the exception). As of a few days ago, my stomach has settled down. I no longer fear what has been called "Beijing Belly" (never mind that I am far north of there in Harbin) though that is more likely something that occurs should one drink the water, something I have not done, and still guard against. So, if you plan on staying in China more than two weeks, your stomach should come around by then.