For me personally, I limit some foods because of how I react to them. For example, I am lactose intolerant since surgery so milk products don't treat me well. I either use Lactaid when eating them or just skip them. I cut down on sugar cause it is a trigger for pouchitis in me because it feeds the bad bacteria. Other foods I do in small portions because of how they loosen or tighten the stool too much. One is raw veggies. I can handle a few carrots, but too many and I have pain when they come out. Another being cheese, too much and my output is so thick that it causes strain, which doesn't feel good either.
Everyone is different. As you progress as a j poucher, you learn what your body is willing to tolerate and what it isn't. I don't believe their is an exact science on it. You know your own personal limits. Some people will keep a food journal to determine what food react a certain way.
Hope this helps answer your question in a round about way