If you look around in PetSmart, you will find several varieties of cat food for sensitive stomachs. Having said that there are a few that are pretty pricey.

I suspect as catnapper says you need to stick with one food, just as she said introduce it gradually and although you may have upset tummies at first, I have found sticking with it often they build a tolerance and are fine after that.

I have that sometimes even when I buy a new bag (Royal Canin Persian Food) even that can but not always can upset one particular kitties tummy.