Carrageenan is a common food additive that is extracted from a red seaweed, Chondrus crispus, which is popularly known as Irish moss. Carrageenan, which has no nutritional value, has been used as a thickener and emulsifier to improve the texture of ice cream, yogurt, cottage cheese, soy milk and other processed foods.
When I first wrote about carrageenan on this site 10 years ago, I reported that some animal studies had linked degraded forms of it (the type not used in food) to ulcerations and cancers of the gastrointestinal tract. But around that time, a prominent researcher in the field, Joanne K. Tobacman, M.D., now associate professor of clinical medicine at the University of Illinois College of Medicine, conducted studies linking undegraded carrageenan - the type that is widely used in foods - with malignancies and other stomach problems. (Degraded and undegraded carrageenan differ by molecular weight with undegraded carrageenan having the higher weight.)
Over the years Dr. Tobacman has published 18 peer-reviewed studies that address the biological effects of carrageenan and is convinced that it is harmful to human health. In April 2012, she addressed the National Organic Standards Board on this issue and urged reconsideration of the use of carrageenan in organic foods.
In her presentation, Dr. Tobacman said that her research has shown that exposure to carrageenan causes inflammation and that when we consume processed foods containing it, we ingest enough to cause inflammation in our bodies. She explained that all forms of carrageenan are capable of causing inflammation. This is bad news. We know that chronic inflammation is a root cause of many serious diseases including heart disease, Alzheimer's and Parkinson's diseases, and cancer.
Dr. Tobacman also told the board that in the past, drug investigators actually used carrageenan to cause inflammation in tissues in order to test the anti-inflammatory properties of new drugs. And she reported further that when laboratory mice are exposed to low concentrations of carrageenan for 18 days, they develop "profound" glucose intolerance and impaired insulin action, both of which can lead to diabetes.
She maintains that both types of carrageenan are harmful and notes that "degraded carrageenan inevitably arises from higher molecular weight (food grade) carrageenan." Research suggests that acid digestion, heating, bacterial action and mechanical processing can all accelerate degradation of food-grade carrageenan.
All told, I recommend avoiding regular consumption of foods containing carrageenan. This is especially important advice for persons with inflammatory bowel disease.
Andrew Weil, M.D.