pb4 is right. Getting IBD doesn't have anything to do with how physically fit you are or how healthy you eat. You have to be genetically predisposed to getting it.
And, no one has proven that UC is communicable. I think Harpo's post may mislead some people (I know that wasn't his intention). The Harvard study posted used animal models and they didn't come to the definite conclusion that UC was communicable.
Better to be safe than sorry..