When I was really sick, my parents wouldn't let me drink any fruit juices. My dad said it was because of the level of acidity.
The same reason applies to any dishes that contain tomato sauce.
Also, I ate a pile of pineapple once and then I had a bloody BM that preceded a trip to the ER. To this day, my dad won't even have it in front of me. It may or may not have been the pineapple's fault, but who knows?
I know it's plain, but it's best to stick with water because it's just safer.