Chitosan

Chitosan is an amino polysaccharide built from two kinds of sugar units, glucosamine and N-acetylglucosamine, joined in a long chain by beta-1,4 glycosidic bonds ^[1][2]. It is manufactured from chitin, the second most abundant natural polymer after cellulose, by a process called deacetylation, in which chitin is treated with a strong alkali such as sodium hydroxide to strip away acetyl groups ^[1][2]. The proportion of units that have been deacetylated, known as the degree of deacetylation, varies between products and influences the material's behavior ^[1]. Pure chitosan does not dissolve in water but dissolves readily in mildly acidic solutions, where its amine groups pick up a positive charge and make the polymer cationic ^[1].

The raw chitin comes mainly from the exoskeletons of crustaceans, a by-product of the seafood industry, and it can also be obtained from fungi ^[1][2]. Because chitosan is biodegradable, biocompatible, generally nontoxic, and mildly antibacterial, it has attracted broad interest as a natural, renewable material ^[2]. It can be processed into many forms, including powders, films, beads, gels, sponges, nanoparticles, and fibers, which underpins its wide range of applications ^[4].

In agriculture, chitosan is used as a seed treatment and biopesticide that stimulates plants' own defenses against fungal disease; it was registered as an active ingredient by the United States Environmental Protection Agency in the 1980s ^[1]. In water treatment it serves as a flocculant that helps clarify water ^[1]. Its biomedical uses are extensive: it appears in hemostatic wound dressings that promote clotting, in tissue-engineering scaffolds for regenerating bone, cartilage, and other tissues, and as a carrier in drug and gene delivery systems, where its stickiness to mucous surfaces and its ability to ease drugs across cell barriers are especially valued ^[2][4]. It is also used in cosmetics ^[2].

Chitosan is widely sold as a weight-loss and cholesterol-lowering supplement, on the premise that it binds dietary fat in the gut and blocks its absorption ^[1][3]. The clinical evidence, however, is unconvincing ^[1][3]. A systematic review of randomized trials found that chitosan produced only a small weight reduction compared with placebo, and that this effect shrank further when the analysis was limited to larger, higher-quality studies, leading the reviewers to judge any benefit as minimal and unlikely to be clinically meaningful ^[3]. Regulators have likewise warned consumers about exaggerated weight-loss marketing ^[1].

Chitosan is regulated as a dietary supplement and as an industrial and agricultural material rather than as an approved drug for weight loss, and it is available in capsules, tablets, and powders as well as in many non-food products ^[1]. It is generally well tolerated, with digestive complaints such as constipation or bloating being the most common issues, and because it can bind fats it may in theory reduce absorption of fat-soluble vitamins or certain medicines ^[3]. As most commercial chitosan is derived from shellfish, people with shellfish allergy are often advised to be cautious ^[1].

Generally well tolerated; the main complaints are constipation, bloating and gas. Because it is made from shellfish, people with shellfish allergies should be cautious. It can theoretically reduce absorption of fat-soluble vitamins and some medications, so space it away from those.