Carrageenan, a heavily discussed additive in the world of alternative health, is an indigestible polysaccharide that is extracted from red algae, and is most commonly used in food as a thickener or stabilizer. Carrageenan-containing seaweeds have been used for centuries in food preparations for their gelling properties, but the refined, isolated carrageenan found in modern processed foods has raised concerns in the health-conscious online community. (1)

Carrageenan is especially common in non-dairy milks such as almond milk and coconut milk, which means that some people who transition to a Paleo diet might actually be increasing their exposure if they use these products. I discussed carrageenan on a recent podcast, but today I want to give you a more detailed summary of the evidence.

Hold the almond milk… is carrageenan affecting your health?

There are a few distinct types of carrageenan that differ in their chemical properties, but the most important distinction is between degraded carrageenan and undegraded carrageenan. From a chemical standpoint, the difference between these two types is in their molecular weight. From a practical standpoint, undegraded carrageenan is approved for use in food products, while degraded carrageenan is not. (2) Although both substances are often referred to as ‘carrageenan,’ they have very different chemical properties and should really be treated as separate compounds. Degraded carrageenan is also called ‘poligeenan,’ which is how I will refer to it in the rest of this article to avoid any confusion.

Animal Studies

Most of the carrageenan hysteria stems from animal studies that implicate carrageenan in the formation of ulcerations and cancerous lesions in the colon. A thorough review of the approximately 45 available animal studies on carrageenan was published in 2001, and at first glance, these studies seem alarming. However, it turns out that the majority of these animal experiments used poligeenan instead of carrageenan, and as I mentioned before, 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 has given carrageenan a worse reputation than it deserves.

One important difference is that while poligeenan can cause cancer on its own when given in high enough concentrations, undegraded carrageenan has only ever been shown to accelerate cancer formation when administered with a known carcinogen. (3) In other words, food-grade carrageenan has not been shown to cause cancer in animal models. That doesn’t necessarily mean carrageenan is in the clear when it comes to cancer, but contrary to popular belief, it is not a known carcinogen.

Additionally, poligeenan produces more severe ulceration and inflammation than carrageenan, and at lower concentrations. As an example, a study on rhesus monkeys using poligeenan at 0.5-2% resulted in diarrhea, hemorrhage, and ulcerations, while carrageenan at 1-3% resulted in no colonic changes. (4) (For reference, the concentration of carrageenan in processed food is usually between 0.01% and 1%.) (5)

However, carrageenan has produced intestinal damage in some animal studies. Observed effects in rats include epithelial cell loss, increased intestinal permeability, and diarrhea. (6) In guinea pigs, carrageenan at a 5% concentration in the diet caused ulcers in the colon, although a similar concentration in the diets of rats and hamsters resulted in no difference from controls. (7) In pigs, concentrations of carrageenan between .05 and .5% administered for 83 days resulted in abnormalities in the intestinal lining, but no ulcerations or tumors. (8) Still, a more recent rat study found no ulcerations or lesions in the colon after 90 days of carrageenan administration. (9) These studies suggest that the effects of carrageenan are highly species-dependent, which makes it more difficult to extrapolate these results to humans.

There are a few other important considerations when determining how applicable these results are to humans. Many of these experiments administered the carrageenan through the animals’ drinking water as opposed to their food, which tends to increase the severity of the resulting symptoms. Because carrageenan interacts with protein molecules, consuming it as part of a solid food is much less harmful than consuming it in water. Also, although many of the concentrations administered are comparable to concentrations found in processed foods, many experiments were conducted at concentrations much higher than humans would ever encounter on a normal diet. Remember, these studies are looking at carrageenan as a percentage of the entire diet, not just less than 1% of a small portion of the total diet, as is the case when using milk replacement products.

Human Studies

Experimental evidence on the effects of carrageenan in humans is extremely limited, for obvious ethical reasons. However, a few in vitro experiments have been conducted on isolated human intestinal cells.

One study found that in intestinal epithelial tissue, carrageenan exposure increased the expression of two pro-inflammatory transcription factors. (10) This reaction appears to be protective of the intestinal tight junctions, because suppression of either of the inflammatory factors resulted in increased permeability of the isolated epithelial tissue. Unfortunately, it’s unclear whether they used food-grade carrageenan rather than poligeenan in this experiment.

Two similar studies that did use food-grade carrageenan also found that isolated intestinal epithelial tissue responded to carrageenan by up regulating inflammation. (11, 12) Another study on human intestinal epithelium found that undegraded carrageenan reduced the activity of many sulfatase enzymes, with potential negative ramifications for the function and vitality of the cell. (13)

Finally, 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. (14)

These studies provide some support for the generalization of the animal studies to humans, implicating carrageenan in the potential for intestinal inflammation. However, it’s important to remember that not only were these studies in vitro (aka not in the human body), they also didn’t administer the carrageenan with any food, so the effects observed may differ significantly from what actually occurs when humans ingest carrageenan in a real-world setting.

Exposure to Poligeenan

Because poligeenan can be produced from carrageenan, many researchers and laypeople have expressed concern that we might be exposed to poligeenan through contamination of the food supply. However, the most recent sources indicate that the poligeenan contamination level of food-grade carrageenan is less than 5%. (15)

Another encouraging data point in this situation is that while carrageenan is an extremely effective thickener and emulsifier at concentrations as low as .01%, poligeenan has no functional effect in food even at concentrations up to 10%. (16) Specific chemical processing is necessary for carrageenan to be degraded to poligeenan, and because poligeenan is of no use in the food industry, it seems unlikely that poligeenan would show up in appreciable quantities in processed foods.

Another concern is whether small percentages of ingested carrageenan are degraded to poligeenan in the digestive tract after consumption, either because of the acidic environment or because of intestinal bacteria. Some experimental evidence indicates that as much as 10-20% of carrageenan could be degraded to poligeenan during digestion, while other researchers (not surprisingly funded by the carrageenan industry) assert that carrageenan is stable throughout digestion. (17, 18) Regardless, the significant differences between poligeenan and carrageenan as evidenced by the reactions of lab animals make it pretty clear that even if some degradation does take place, carrageenan still doesn’t have the potential for harm that poligeenan does.

Conclusion

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

However, I do still think caution is warranted. If I had to rank additives, I’d say carrageenan is a bit more concerning than the other two additives we’ve discussed so far because of its association with gut issues. Remember, 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 adhere to the “precautionary principle” 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 reading this, avoiding carrageenan is probably as simple as making your own nut milk or coconut milk, so I would encourage you to give that a shot. Also, if you follow the links to those two posts, some commenters have shared brands of almond and coconut milk that don’t contain carrageenan (although watch out for other additives that may be present).