Chitosan quick review

• Description: a dietary fiber derived from chitin, a biodegradable cationic biopolymer achieved by the extensive deacetylation of chitin obtained from prawn shell waste.

• Health benefits: used mainly as weight-loss agents that act by preventing the absorption of dietary fats from the intestines, an effective hypocholesterolemic agent to lower blood serum cholesterol levels.

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Chitosan

Chitosan is a linear polysaccharide composed of randomly distributed ß-(1-4)-linked D-glucosamine (deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). Chitosan is a partially deacetylated polymer of N-acetyl glucosamine. It is essentially a

natural, water-soluble, derivative of cellulose with unique properties. Chitosan is an amino polysaccharide that has the ability to "bind" lipids in the stomach before they are absorbed through the digestive system into the bloodstream. Chitosan is a biodegradable cationic biopolymer achieved by the extensive deacetylation of chitin obtained from prawn shell waste. Chitosans are biopolymers which belong to the group of hydrocolloids. In contrast to most hydrocolloids, which are negatively charged at biological pH values, chitosans are cationic biopolymers under these conditions.

Chitosan is a dietary fiber derived from chitin. Chitin is typically prepared from waste shells of crustaceans, particularly decapod crustaceans such as crab, shrimp, crawfish, krill, lobster, squid and prawn. Removal of acetyl groups from the chitin polymer (deacetylation) produces chitosan. Chitosan is not a single, definite chemical entity since it varies in composition depending on the crustacean species used for the starting material and the particular preparation method used. Reducing or substantially removing impurities from chitosan that can cause immunological reactions is critical for chitosan intended for use as a biocompatible and biodegradable material in medical applications. Chitin and chitosan refer to a family of compounds that exhibit widely differing physical and chemical properties. These differences are due primarily to the products' varying molecular weights, degrees of acetylation and presence of contaminants such as covalently bound, species-specific proteins, single amino acid and inorganic contaminants.

Mechanism of action

Like dietary fiber, chitosan is not digestible but may have beneficial effects on the gastrointestinal tract. Chitosan may also have an effect on the type of bacteria living in the intestines or on the action of these bacteria. Chitosan is, at the pH of the gastrointestinal tract, a positively charged polymer and can bind to negatively charged substances. It is believed that chitosan, similar to cholestryamine, has bile acid sequestration activity and that this may be the mechanism for its hypocholesterolemic effect. The amino group in chitosan has a pKa value of ~6.5, thus, chitosan is positively charged and soluble in acidic to neutral solution with a charge density dependent on pH and the %DA-value. In other words, chitosan is bioadhesive and readily binds to negatively charged surfaces such as mucosal membranes. The positive charge is supposed to attract negatively charged bile acids and free fatty acids. The bound acids cannot be absorbed thus preventing an increase in dietary fat. Chitosan enhance the transport of polar drugs across epithelial surfaces, and is biocompatible and biodegradable.

Indications and usage

Chitosan is used for a wide variety of purposes including plant care, cosmetics additives, food and nutrition supplements and medical care. Chitosan supplements are promoted as weight-loss agents that act by preventing the absorption of dietary fats from the intestines. Like some plant fibers, chitosan is not digestible; therefore it has no caloric value. This is a very important property for any weight-loss product. Unlike plant fibers, chitosan's unique properties give it the ability to significantly bind fat, acting like a "fat sponge" in the digestive tract. Chitosan purports to have the capability of attracting fat from the digestive system and expelling it from the body so that users can, it is claimed, lose weight without eating less. Chitosan has the very unique ability to lower LDL cholesterol while boosting HDL cholesterol. Chitosan appears to be an effective hypocholesterolemic agent. It can effectively lower blood serum cholesterol levels with no apparent side effects. When used topically, it can aid healing and recovery from skin grafts. Chitosan has also been found to have anti-fungal and anti-bacterial properties and can be applied to the skin to heal wounds more effectively.

Chitosan for weight loss

Chitosan supplements are marketed as `fat blockers' or `fat trappers'. It is claimed that chitosan blocks the absorption of as much as 120 g of dietary fat per day, and this will promote weight loss. Besides from the obvious effect that fat is not absorbed into the body with the presence of chitosan, it goes a lot deeper in benefiting weight loss. Chitosan is a 100% natural and acts as a super fiber. Thus, supplementing the diet with chitosan, is part of creating a cleansing process which is said to be extremely vital to weight loss. The benefits of chitosan in weight loss can be greatly boosted by the simple additions to go along with the chitosan supplements. D-Ascorbic acid (erythorbic acid) and L-ascorbic acid are C vitamins which enhance chitosan's ability to bind lipids. Combining chitosan with ascorbic acid results in even less fat absorption and greater fecal fat losses. Citric acid may enhancethe swelling action of chitosan leading to a sense of fullness, producing satiety and appetite suppression.