(Note: Carrageenan is not part of the SCD diet)
Carrageenan is a seaweed derived additive often used to thicken dairy products such as ice cream. In 2001, carrageenan attracted some notoriety after a study questioned its safety in human food products. Here is a 2001 excerpt from a news story about the study:

"Evidence from animal models has demonstrated that degraded carrageenan causes ulcerations and malignancies in the gastrointestinal tract," said Joanne Tobacman, M.D., University of Iowa assistant professor of clinical internal medicine. [note: Dr. Tobacman now teaches at the University of Illinois medical school]

The study and proceeding articles started a carrageenan "war" with studies and companies taking sides on the issue.

In general there are several types of carrageenan including degraded carrageen and undegraded carrageenan. The degraded carrageenan is harmful. One way to cause IBD in rats is to feed them degraded carrageenan--this induces ulcerative colitis. However, small amounts of undegraded carrageenan were generally deemed safe for ingestion. Tobacman argued that the process of digestion could degrade carrageenan so that by the time it hit the gut, it could cause harm. In addition small amounts were "safe" but
everal years ago