Chitin-chitosan: properties, benefits and risks

A beneficial effect of chitin-chitosan as a food supplement is the reduction of plasma cholesterol and triglycerides due to its ability to bind dietary lipids, thereby reducing intestinal lipid absorption. The hypolipidemic influence of chitosan may also be due to interruption of the enterohepatic bile acid circulation. Plasma cholesterol in animals on cholesterol-free diet, however, is not affected, indicating that endogenous biosynthesis of cholesterol remains intact. Chitosan acts by forming gels in the intestinal tract which entrap lipids and other nutrients, including fat soluble vitamins and minerals, thus interfering with their absorption. Dietary chitosan may influence calcium metabolism by accelerating its urinary excretion. The reported undesirable effects are a marked decrease in plasma vitamin E level, reduction in bone mineral content and growth retardation. Ascorbic acid enhances gel formation of chitosan, thereby potentiating the plasma cholesterol lowering activity. Bile acid composition and short-chained fatty acid content in the cecum are altered by chitosan which impedes lipid emulsification and absorption. Although the increase in lipid content of feces does not appear to alter gastrointestinal functions, it may potentially aggravate the symptoms of mild steatorrhea. Chitin-chitosan inhibits in vitro growth of microorganisms including Candida and in vivo has a protective effect on Candida infection. The antibacterial and antiyeast activities of chitosan are desirable properties and may be useful in preventing infection of wounds by direct application. On prolonged ingestion, however, it may alter the normal flora of the intestinal tract which may result in the growth of resistant pathogens. Although studies with cells, on tissues and animals indicate that chitin-chitosan promotes wound healing, increases immune response, and possesses antitumor activity, these claims need to be further validated in human subjects by clinical trials. Chitin-chitosan, when used as a food supplement, does lower plasma cholesterol and triglycerides and improves the HDL-cholesterol/total cholesterol ratio. Certain medical precautions, however, should be observed with long-term ingestion of high doses of chitosan to avoid potential adverse metabolic consequences.