Wow, there is so much misinformation posted here, very misleading for someone who does not know any better. I have had UC for close to 25 years and I am fortunate enough to have a Dr. that is a world leading expert on the disease. Here is what I have learned from him:
1) The disease is caused by a combination of microbes, genetics and other factors. Currentl over 100 genes know to be related to the cause. 2) Diet and stress are not factors in causing it or in flare-ups. Certainly changing to a vegan diet or something like this will not cure it, if it was that easy we would all be cured by now. 3) In almost any double blind clinical trial they conduct, about 30% of people get better (and I am guessing temporarily better) with the placebo. Its just the way it is, so if all of us go vegan, 30% will get better.
If you are new to this, educate yourself and try to figure out what works for you personally as everyone is different.
I suggest you read this book, it's a fantatic resource. http://www.amazon.ca/Crohns-Disease-Ulcerative-Colitis-ebook/dp/B008BHUIKG/ref=sr_1_2?ie=UTF8&qid=1370479428&sr=8-2&keywords=saibil