The carrageenan controversy stems from mostly animal studies that claim carrageenan in the formation of ulcerations and cancerous lesions in the colon. This post summarizes results of five separate studies on carrageenan and presents my argument for caution when choosing foods including carrageenan in your diet.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1242073/

Including roughly 45 available animal studies on carrageenan, this report was published in 2001. The majority of these animal experiments used poligeenan instead of carrageenan, these are two separate compounds with different effects. Poligeenan is significantly more detrimental to the health of lab animals than carrageenan, so the lack of a clear designation between them understandably, has given carrageenan a worse reputation than maybe it deserves.

In my clinical experience, and of the research I have seen, carrageenan has produced intestinal damage in some animal studies. In rats there was epithelial cell loss, increased intestinal permeability, and diarrhea.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1242073/

In a recent rat study, there was found to be no ulcerations or lesions in the colon after 90 days of carrageenan administration.

http://www.ncbi.nlm.nih.gov/pubmed/17034924

In reading these articles and others, the effects of carrageenan seem to be species-dependent, which makes it more difficult to relate results to humans.

So yes, as you have stated, there are a few other important considerations when determining how applicable these results are to humans. Many of the experiments indeed administer the carrageenan through the animals’ drinking water as opposed to their food, which tends to increase the severity of the resulting symptoms. Since carrageenan interacts with protein molecules, consuming it as part of a solid food is probably less harmful than consuming it in water. Some of the concentrations administered are comparable to concentrations found in certain processed foods, however, experiments were conducted at concentrations higher than we would potentially ever encounter.

Understanding this, experimental evidence on the effects of carrageenan in humans is extremely limited. On the other hand, I have come across a few in vitro experiments on isolated human intestinal cells. One study I found interesting was from Science Direct, where in intestinal epithelial tissue, carrageenan exposure increased the expression of two pro-inflammatory transcription factors.

http://www.sciencedirect.com/science/article/pii/S0378427412009423

This reaction appears to be protective of the intestinal tight junctions, since suppression of the inflammatory factors resulted in increased permeability of the isolated epithelial tissue. However, I am unclear whether they used food-grade carrageenan or poligeenan in this experiment. I found two similar studies that did use food-grade carrageenan that found that isolated intestinal epithelial tissue responded to carrageenan by up regulating inflammation.

http://ajpgi.physiology.org/content/292/3/G829
http://www.ncbi.nlm.nih.gov/pubmed/22579587

Another study found that exposing human intestinal epithelial cells to undegraded carrageenan in concentrations lower than what would be found in a typical diet caused increased cell death, reduced cell proliferation, and cell cycle arrest.

http://jn.nutrition.org/content/138/3/469.short

These studies provide some support for the generalization of the animal studies to humans, implicating carrageenan in the potential for intestinal inflammation. However, they are not in vitro, they also didn’t administer the carrageenan with any food, so the effects observed may differ from what actually occurs when humans ingest carrageenan in a real-world setting.

So, carrageenan has been frequently portrayed as significantly more harmful than is potentially supported by available evidence. Contrary to popular belief, it’s not a known carcinogen, some studies implicate carrageenan in ulceration and inflammation, some show no adverse effects.

However, I still feel caution is warranted. In practice, I have seen the suggestion of staying away from additives such as carrageenan to alleviate gut issues. I do believe in cases involving modern ingredients, the burden of proof should be on manufacturers to prove that they’re safe, rather than on consumers to prove that they’re harmful. Because the evidence isn’t conclusive either way, I recommend avoiding carrageenan, especially if you have a history of digestive problems.

Personally, I believe in balance for anything I eat; in other words, in the absence of proven safety, I choose to avoid foods that have questionable adverse effects. Carrageenan fits this description, as there’s still some doubt about its safety and no evidence has convinced me that there isn’t a potential for harm if consumed regularly.

Occasional exposure is likely nothing to worry about, but for most people in my practice, avoiding carrageenan is probably as simple as making your own alternative milk, such as almond, or coconut.

-Dr. Seema Kanwal N.D.