Pop corn is one of those foods that is techincally fine around list 4/5. However–this is a very individual type thing as is true with many of the foods within those lists.
The diet lists are defintiely skeletons that I go by and we individualize depending on the person. Foods that are very highly fibrous as is the case with popcorn can be abrasive to the intestines and therefor cause more problems with intestinal leakage. So, if you are eating popcorn and finding that you are flaring, this is likely why.
So, becareful-this is not a food that should be consumed without a lot of attention to reactivity.
Dr.M