Chitosan

Overview

Chitosan is a form of fiber that is derived by deacetylating a polysaccharide known as chitin. Chitosan polymers are thought to contain more than 5,000 repeating acetylglucosamine and glucosamine units. (1) The best sources of chitin are the exo-skeletons of various crustaceans such as shrimp, crabs, squid, and other shellfish. (2) When taken orally, chitosan has the unique ability to bind to fat in the stomach, which prevents the fats from being absorbed into the body. A factor that makes chitosan a unique form of fiber is that it carries a strong positive charge, which enables it to “magnetically" attract and bind negatively charged substrates such as lipids. (3) In fact, this is the explanation of why and how chitosan prevents the absorption of fats.

Chitosan’s fat-blocking ability has been demonstrated in animal studies where chitosan given orally in lab chow resulted in a substantial lowering of cholesterol absorption and an increase in fecal fat excretion. (4) One study measured the amount of fat that was excreted by mice that were fed either cellulose (as a control fiber) or chitosan. In the control mice, approximately 95% of the dietary fat was absorbed while 5% was excreted. In the mice receiving chitosan, only about 51% of dietary fat was absorbed with slightly more than 49% being excreted. Thus, chitosan caused nearly a 50% reduction in the absorption of dietary fats. (5) Human studies suggest that chitosan may indeed reduce the body's absorption of cholesterol. (6) , (7)

Researchers in Japan have reported that chitosan also has anti-ulcer effects. In rats with chemically induced ulcers, chitosan protected gastric cells from damage, increased the level of gastric mucus secretion, and promoted the healing of existing ulcers. (8) These same researchers also reported a large range in the molecular weights of chitosan polymers. Low molecular weight chitosans weigh from 25-50 kiloDaltons and high molecular weight chitosans weigh from 500-1,000 kiloDaltons. In this particular study, the low molecular weight chitosan product provided substantial anti-ulcer activity whereas the high molecular weight chitosan provided very little benefit. Another study involving 122 patients with gastric and duodenal ulcers were treated with chitosan and found that H. pylori was suppressed, effective for sanitation of mucosa and accelerated ulcers cicatrization. (9)

Because of its ability to prevent the absorption of dietary fat, chitosan is frequently promoted as a weight loss product. However, scientific studies thus far have not provided much support for this claim.

Dosage Info

Dosage Range

One to two grams at or before meals when an individual wants to prevent the absorption of fats.

Most Common Dosage

Not Applicable.

Dosage Forms

Capsules and tablets.

Adult RDI

None established

Adult ODA

None established

RDA

  • None established:

Interactions and Depletions

Interactions

Active Forms

Chitosan (pronounced kite-o-san)

Absorption

Chitosan is not absorbed. It passes through the human digestive tract and is eliminated from the colon along with the fats that it has picked up during its transit through the gastrointestinal tract.

Toxicities & Precautions

General

Chitosan is non-toxic and no serious side effects have been reported. However, since chitosan prevents the absorption of fats, it should not be taken along with fat-soluble vitamins and it may inhibit the absorption of some medications.

Functions in the Body

Dietary fat

Chitosan binds fat in the stomach and intestines, which decreases the amount of dietary fat that is absorbed into the body.

Clinical Applications

Elevated Cholesterol

The results of studies with laboratory animals (10) and humans (11) report that chitosan reduces cholesterol absorption. In one study, chitosan-fed mice had a 64% lowering of cholesterol levels compared to control animals. Comparrison of aortic plaque deposits in the two groups of animals revealed that the level of cholesterol lowering in the animals fed chitosan resulted in a significant inhibition is the development and progression of atherosclerosis. (12) In another study, the cholesterol-lowering effects of chitosan, cholestyramine, and oat gum were compared in groups of rats. Chitosan and cholestyramine both produced a significant lowering of serum cholesterol levels while oat gum was less effective. (13) While chitosan and cholestyramine produced similar cholesterol-lowering effects, it was noted that cholestyramine caused abnormal changes in the mucosal cells lining the small and large bowel while chitosan did not cause any detrimental cellular changes.

Weight Loss

Because they prevent the absorption of fats, chitosan products have become popularized as commercial weight loss products. Although there is a theoretically plausible rationale for these products, studies in which chitosan was administered to overweight humans have not resulted in weight reduction. (14) , (15)

Wound dressings

Various products made from chitosan are being developed for use as wound dressings. Chitosan membranes facilitate controlled water evaporation, excellent oxygen permeability and enable fluid drainage while also inhibiting invasion by exogenous microorganisms. (16) Some dressings combine chitosan with other solvents such as acetic acid or lactic acid. In a comparrison of several types of dressings, the chitosan/lactic acid dressing performed best, providing a very soft, flexible, pliable bioadhesive dressing. (17)

Skin Grafts

When applied topically to skin grafts, chitosan becomes a semi-permeable dressing that maintains a sterile wound exudate beneath a dry scab. This reduces dehydration and contamination of the wound, which optimizes conditions for healing. (18) , (19)

Symptoms and Causes of Deficiency

Chitosan is not a nutrient for humans so there is no deficiency condition.

Dietary Sources

Chitosan is not part of foods that humans normally consume.

References

  1. View Abstract: Han LK, Kimura Y, Okuda H. Reduction in fat storage during chitin-chitosan treatment in mice fed a high-fat diet. Int J Obes Relat Metab Disord. Feb1999;23(2):174-9.
  2. View Abstract: Shepherd R, Reader S, Falshaw A. Chitosan functional properties. Glycoconj J. Jun1997;14(4):535-42.
  3. View Abstract: Ormrod DJ, Holmes CC, Miller TE. Dietary chitosan inhibits hypercholesterolaemia and atherogenesis in the apolipoprotein E-deficient mouse model of atherosclerosis. Atherosclerosis. Jun1998;138(2):329-34.
  4. View Abstract: Gallaher CM, Munion J, Hesslink R, et al. Cholesterol reduction by glucomannan and chitosan is mediated by changes in cholesterol absorption and bile acid and fat excretion in rats. J Nutr. Nov2000;130(11):2753-9.
  5. Deuchi K, Kanauchi O, Imasato Y, et al. Decreasing Effect of chitosan on the apparent fat digestibility by rats fed on a high-fat diet. Biosci Biotech Biochem. 1994;58(9):1613-1616.
  6. View Abstract: Bokura H, et al. Chitosan decreases total cholesterol in women: a randomized, double-blind, palcebo-controlled trail. EJCN. May2003;57(5):721-725.
  7. View Abstract: Ausar SF, Morcillo M, Leon AE, et al. Improvement of HDL- and LDL-cholesterol levels in diabetic subjects by feeding bread containing chitosan. J Med Food. Dec2003;6(4):397-9.
  8. View Abstract: Ito M, Ban A, Ishihara M. Anti-ulcer effects of chitin and chitosan, healthy foods, in rats. Jpn J Pharmacol. Mar2000;82(3):218-25.
  9. View Abstract: Bondarenko VM, Chervinets VM, Vorob'ev AA. Role of persisting opportunistic bacteria in the pathogenesis of the gastric and duodenum ulcer. Zh Mikrobiol Epidemiol Immunobiol. Jul2003;(4):11-7.
  10. View Abstract: Gallaher CM, Munion J, Hesslink R, et al. Cholesterol reduction by glucomannan and chitosan is mediated by changes in cholesterol absorption and bile acid and fat excretion in rats. J Nutr. Nov2000;130(11):2753-9.
  11. View Abstract: Muzzarelli RA. Clinical and biochemical evaluation of chitosan for hypercholesterolemia and overweight control. EXS. 1999;87:293-304.
  12. View Abstract: Ormrod DJ, Holmes CC, Miller TE. Dietary chitosan inhibits hypercholesterolaemia and atherogenesis in the apolipoprotein E-deficient mouse model of atherosclerosis. Atherosclerosis. Jun1998;138(2):329-34.
  13. View Abstract: Jennings CD, Boleyn K, Bridges SR, et al. A comparison of the lipid-lowering and intestinal morphological effects of cholestyramine, chitosan, and oat gum in rats. Proc Soc Exp Biol Med. Oct1988;189(1):13-20.
  14. View Abstract: Pittler MH, Abbot NC, Harkness EF, Ernst E. Randomized, double-blind trial of chitosan for body weight reduction. Eur J Clin Nutr. May1999;53(5):379-81.
  15. View Abstract: Egger G, Cameron-Smith D, Stanton R. The effectiveness of popular, non-prescription weight loss supplements. Med J Aust. Dec1999;171(11-12):604-8.
  16. View Abstract: Mi FL, Shyu SS, Wu YB, et al. Fabrication and characterization of a sponge-like asymmetric chitosan membrane as a wound dressing. Biomaterials. Jan2001;22(2):165-73.
  17. View Abstract: Peh K, Khan T, Ch'ng H. Mechanical, bioadhesive strength and biological evaluations of chitosan films for wound dressing. J Pharm Pharm Sci. Sep2000;3(3):303-11.
  18. View Abstract: Stone CA, Wright H, Clarke T, et al. Healing at skin graft donor sites dressed with chitosan. Br J Plast Surg. Oct2000;53(7):601-6.
  19. View Abstract: Azad AK, Sermsintham N, Chandrkrachang S, Stevens WF. Chitosan membrane as a wound-healing dressing: characterization and clinical application. J Biomed Mater Res. May2004;69B(2):216-22.