Carrageenan and gut ulcers and tumours in animal tests
What it found
In animal experiments, carrageenan was linked to intestinal ulcers and tumours, and the author says the widespread use of carrageenan in the Western diet should be reconsidered.
What they found
Animal and lab studies
Tumours in animals
In rats fed 10% degraded carrageenan in the diet for less than 24 months, 32% developed colonic tumours, including squamous cell carcinomas, adenocarcinomas, and adenomas. With 5% degraded carrageenan in drinking water, there was a 100% incidence of colonic metaplasia after 15 months.
Carrageenan as promoter
In rats given a known carcinogen, adding undegraded carrageenan to the diet led to tumours in 100% of animals, compared with 57% with the carcinogen alone. Carrageenan alone led to tumours in 7% of rats, and controls had 0%.
Intestinal ulcers
Many studies found ulcers in the cecum or large intestine of guinea pigs, rabbits, mice, rats, and rhesus monkeys after they were given carrageenan. In guinea pigs given 2% degraded carrageenan as liquid for 20 to 30 days, 100% had colonic ulcerations and 75% had more than 200 ulcers.
Dose and duration
Ulcerations were dose dependent and related to how long the animals were exposed. In rabbits given 0.1% degraded carrageenan in drinking fluid, 60% developed ulcerations, while 100% of those given 1% had ulcerations after 6 to 12 weeks.
Undegraded carrageenan
Undegraded carrageenan was also linked to ulcers and tumours in animal studies. In guinea pigs given 1% undegraded carrageenan as liquid for 20 to 30 days, 80% developed colonic ulcerations.
Other findings
How it may happen
The author suggests that carrageenan may break down into smaller pieces during normal digestion or by gut bacteria, and that these smaller pieces may be taken up by macrophages and cause ulcers. Food-grade carrageenan can also contain some degraded carrageenan as a contaminant.
What the authors conclude
“Because of the acknowledged carcinogenic properties of degraded carrageenan in animal models and the cancer-promoting effects of undegraded carrageenan in experimental models, the widespread use of carrageenan in the Western diet should be reconsidered.”
Also in their conclusions
- They say that because degraded carrageenan is acknowledged to have carcinogenic properties in animal models and undegraded carrageenan has cancer-promoting effects in experimental models, the widespread use of carrageenan in the Western diet should be reconsidered.
- They note that no legislative protection has been enacted to restrict the incorporation of low molecular weight fractions of carrageenan into food.
How it was done
The author was concerned that carrageenan is widely used in processed foods even though the International Agency for Research on Cancer in 1982 found enough evidence for the carcinogenicity of degraded carrageenan in animals to regard it as posing a carcinogenic risk to humans.
The author reviewed published animal experiments that tested carrageenan in guinea pigs, rats, monkeys, mice, rabbits, and ferrets. The studies used different doses, routes, and durations, and most compared carrageenan-exposed animals with control animals.
What it can’t tell you
- These are animal experiments. They cannot show what happens in people.
- The paper does not report any studies in people that tested whether carrageenan causes ulcers or cancer.
- The author's calculations about human intake are estimates, not measurements of what happens in people.
Who paid
- Authors work at
- University of Iowa, USA
The paper
- Title
- Review of harmful gastrointestinal effects of carrageenan in animal experiments
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Animals and lab studies
- Summarised from
- Full text
- Cite
- Tobacman JK (2001). Review of harmful gastrointestinal effects of carrageenan in animal experiments. Environmental health perspectives. doi:10.1289/ehp.01109983Free full textPubMed 11675262DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error