Carrageenan, an extract of red seaweed, is a good
source of soluble fiber. It is widely used in the food
industry, for its gelling, thickening, and stabilizing
properties. Carrageenan is a vegetarian and vegan
alternative to gelatin in some applications. It has
also been the subject of many long-term dietary studies under
defined regulatory conditions en route to its current global
regulatory status. While some indicate that carrageenan safely
passes through rat GI tracts without adverse effect when it is a
dietary ingredient, other animal dietary studies have observed
colitis-like disease and tumor promotion. This has caused
some people to be concerned about the safety of carrageenan
when used in dietary supplements.
The question of safety
So what is the bottom line? Is carrageenan a safe or unsafe
dietary ingredient for humans? To answer this question, it
is important to consider the amount of carrageenan used in
animal studies. In a published scientific review called, "Review
of Harmful Gastrointestinal Effects of Carrageenan in Animal
Experiments,"1 the author discusses a variety of studies. When
examining those in which the animals consumed carrageenan
in water or food, negative effects were observed at levels of 0.2
to 15 grams per kilogram of body weight. That would translate
to 15 to 1,125 grams of carrageenan daily for a 165 pound human
being. At the high end of that range, that's the equivalent of
eating 4500 calories a day just from carrageenan alone. My
point is, the amounts used in these studies are typically far
more than people would likely consume on a daily basis in
dietary supplements; and speaking of people, it is important to
note that the concerns about the use of carrageenan are based
solely upon animal studies, not human studies. Nevertheless,
there are human studies on carrageenan, and the results are
different than those of the animal studies.
Human studies on carrageenan
In a double-blind, placebo-controlled study,2 255 patients with
peptic ulcers received 0.75 g of carrageenan or a placebo
each day for 22 months. The results were that, compared to
placebo, carrageenan was effective for the treatment of peptic
ulcer without noticeable side effects (p<0.025). The global
judgment of effectiveness was made based chiefly on the
x-ray and gastroscopic findings, and then on the outcome of
such subjective symptoms as retching, vomiting, nausea, and
anorexia.
Another randomized crossover study3 aimed to determine
the effect of carrageenan incorporation into a meal on
carbohydrate absorption in human subjects. The concept
being that soluble fiber decreases the amount of carbohydrates
that reach the bloodstream by delaying their absorption in the
small intestine. This was tested by measuring blood glucose
levels, a reflection of carbohydrate absorption. The total
dietary fiber (TDF) content of the carrageenan (2.03 percent)
meal was about three times that of the control meal (0.68
percent). The meal provided 14.84g (meal with carrageenan)
and 3.45 g of TDF (meal without carrageenan), and were fed
to the same ten fasting subjects at different times. The results
showed the average blood glucose levels of subjects were
significantly lower after consuming the carrageenan meal than
when consuming the regular meal (P <or = 0.05 at 15, 45, and
90 minutes). Likewise, there was a significant lowering of total
cholesterol (P <0.0014) and triglyceride (P <0.0006) levels
after eight weeks with carrageenan. In fact, levels of HDL
cholesterol (the "good cholesterol") increased significantly
(P <0.0071) after eight weeks with carrageenan.

No side effects were reported in the study. The researchers
concluded that the blood sugar lowering-effects of carrageenan
could prove useful in the prevention and management of
metabolic conditions such as diabetes.
There are also some human cell line studies, but I didn't
include data on those because they don't necessarily reflect
what happens in a live human body.
Conclusion
In my opinion, at the doses typically found in dietary
supplements, carrageenan is neither potentially beneficial nor
potentially harmful—there is just too little of it. Personally, I
would not hesitate to use dietary supplements that contain
carrageenan as part of their make-up.
References
- Tobacman JK. Review of harmful gastrointestinal effects of carrageenan in animal experiments. Environ Health Perspect. Oct 2001;109(10): 983–94.
- Yamagata S, Ishimori A, Hachiro S, et al. Clinical Evaluation of Pharmacotherapy for Peptic Ulcer with Antipepsin Agents by Double Blind Technique - Multicenter Clinical Study. Tohoku J Exp Med. 1973;110:377–404.
- Dumelod BD, Ramirez RP, Tiangson CL, Barrios EB, Panlasigui LN. Carbohydrate availability of arroz caldo with lambda-carrageenan. Int J Food Sci Nutr. 1999 Jul;50(4):283–9.