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