I've had the exact problem - when I started South Beach and even now I get flare ups. They treat it like Ischemic Colitis. So I've modified SB to include SOME sort of processed food every day or every other day. I am happy to talk to you more in a PM about it. I've had 7 colonoscopies, 4 endoscopies and 4 hospitalizations since 2007...I feel your pain!
Low residue is not fun - use some SB properties (like cooked vegetables, sweet potatoes not white). Anything cooked is low residue!
Hope it all works out. Keep us updated!
Weight Lost Since January 3, 2015 via South Beach Diet