My vet used to try to get me to put the dogs on the Hills food that he sells. I flat out told him that I wouldn't do it because it's crap food and besides, Spencer is allergic to it. Since then, he just leaves me alone.
I have never seen a bad reaction to the gastro food, if you get that reaction to it, I wouldn't feed it either. I don't care how long they have been on something else, it's supposed to help with the problem, not make it worse. Ugh!!