Yes Please! My 15 Year Old Son Has Been Diagnosed

Yes please! My 15 year old son has been diagnosed with "left-sided ulcerative colitis". He is taking Lialda, but has recently had to supplement with enemas. We have been told that colitis is not controllable with diet the way Crohn's is. But we want to at least start following a nutritional plan that eases digestive discomfort and helps prevent cancer (people with IBS have a 1 in 5 risk of developing colon cancer after 30 years with the disease - he'll be 45). Any advice or books you can recommend?