Carrageenan is a water-soluble polymer, also known as a gum, that thickens and improves the texture of foods such as pudding, ice cream, yogurt and cottage cheese.
Derived from red seaweed, carrageenan also is used as a fat substitute in processed meats and can be found in condensed milk and some soy milk products.
Findings over the years in Europe and the United States suggest that assumptions about the safety of carrageenan need to be reconsidered and that carrageenan may need to be better regulated by the Food and Drug Administration (FDA), said Joanne Tobacman, M.D., UI assistant professor of clinical internal medicine.
"Evidence from animal models has demonstrated that degraded carrageenan causes ulcerations and malignancies in the gastrointestinal tract," said Tobacman, who has conducted epidemiologic and laboratory research on carrageenan.
She recently published an extensive review of 45 investigations on harmful gastrointestinal effects of carrageenan in animal experiments. The article was published in the October issue of Environmental Health Perspectives, the journal of the National Institute for Environmental Health Sciences.
In 1972 the FDA determined there was sufficient evidence from animal experiments to propose limiting the type of carrageenan that could be used in food products. "Many authoritative sources thought that the proposal actually became a regulation. However, it didn't," Tobacman said.
In 1979 the FDA rescinded the proposal, yet at the same time they indicated there would be a more comprehensive regulation in the future. However, no restriction has since been proposed, so there is no substantive regulation of carrageenan in food, Tobacman said.
"It's impossible to reconstruct the thinking that went on in the 1970s about regulating carrageenan," she said. "Apparently the FDA anticipated establishing a more comprehensive regulation, but none has been forthcoming. I find this discrepancy and the continued status of carrageenan as GRAS (generally regarded as safe) very disturbing."
In 1982, the International Agency for Research on Cancer found enough evidence in animal models linking degraded carrageenan with gastrointestinal cancers to state that it posed a carcinogenic risk to humans. Other research groups also have listed it as a known carcinogen based on animal studies.
Degraded carrageenan has a molecular weight of 30,000 or lower, whereas undegraded carrageenan has a molecular weight of 100,000 or higher. Tobacman explained that in addition to evidence that degraded carrageenan causes intestinal ulcerations and cancers, undegraded carrageenan, which has the higher molecular weight and is thought not to be directly absorbed in the intestine, may also be associated with the promotion of malignancy and inflammation in the gastrointestinal tract.
Tobacman explained that stomach acid and food preparation may lead to degraded carrageenan by transforming the higher molecular weight form of the gum into the lower molecular weight form. Bacterial action also may transform higher weight carrageenan into its lower molecular weight form.
"A regulation like the one proposed by the FDA in 1972 might help eliminate some of the low molecular weight components but probably in itself would not be sufficient to prevent all exposure to degraded carrageenan because the higher weight form can be transformed into lower weight products," Tobacman said.
Carrageenan use was patented in the 1930s and came into increasingly widespread use in the United States during the second half of the 20th century. It originally was used as a thickener in Irish pudding and was incorporated into different types of processed foods as they became more common in the Western diet. It also has been used in cosmetics, toothpaste and room fresheners.
Tobacman said other gums with similar thickening properties can be used instead of carrageenan. These gums include locust bean, guar and xanthan.
Reading the ingredients on a label can reveal whether carrageenan is part of the food. However, since carrageenan can be a secondary ingredient, for example, included in condensed milk, it may not always be listed by name.
"There seems to be enough evidence associating carrageenan with significant gastrointestinal lesions, including malignancies, to avoid ingesting it," Tobacman said.
"There is a lot to think about but I think the first consideration is to inform people about the risks that have been associated with carrageenan," she added. "There was evidence back in the 1970s that carrageenan has harmful effects, and I think we've waited too long to act on that information."
Tobacman has studies underway to review the carcinogenic mechanisms associated with carrageenan and to identify possible links to breast cancer.
Librarians from the UI Hardin Library for the Health Sciences assisted Tobacman with research for her recent article that was published in Environmental Health Perspectives.
[Contact: Becky Soglin ]