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Ads for chitosan claim it can lower cholesterol and produce rapid weight loss by blocking the absorption of fat. Is this true?
Chitosan is derived from chitin, a polysaccharide found in the exoskeleton of shellfish such as shrimp, lobster, and or crabs. Many sellers claim that chitosan causes weight loss by binding fats in the stomach and preventing them from being digested and absorbed. Some refer to it as a "fat magnet." It is even marketed as a weight-control product for dogs.
Although chitosan can decrease fat absorption, the amount contained in the capsules is too small to have much of an effect on cholesterol levels. Moreover, with better, more predictable cholesterol-lowering products available, it doesn't make much sense to use chitosan for that purpose. There is no evidence that chitosan is effective for weight control.
The British Advertising Standards Authority has upheld complaints about chitosan products advertised by eight companies. In the case where "Fat Magnets" capsules were described as "the much acclaimed fat absorbing food supplement," the Authority concluded:
The advertisers said the product was sold not on a slimming platform but on the grounds that, by absorbing fat, it prevented weight gain. They argued that the advertisement was for a food supplement, not a slimming aid, and was therefore not subject to Clause 51. [This clause states: Any claims made for the effectiveness or action of a slimming method or product should be backed where appropriate by rigorous practical trials on people; testimonials that are not supported by trials do not constitute substantiation.] The advertisers provided a technical report of the product's contents (which included Chitosan) and copies of nearly 30 trials carried out on animals, in vitro, and on humans. They provided the results of a telephone survey of 201 people. The Authority noted that respondents to the survey did not see the name in context and considered that readers would infer from the advertisement, partly because of the product's name, that the tablets would aid weight loss. Some of the trials showed a relationship between the consumption of Chitosan and weight loss over a four-week period for, in aggregate, a large number of people. The Authority took expert advice and concluded that there were many problems with, and incompatibilities between, the trials. It noted that the human trials that showed weight loss had appeared in a toxicology journal that was not known internationally for its expertise in weight-related matters. The Authority acknowledged the volume of material amassed by the advertisers but concluded that, because of the shortcomings in the reports of the trials, the ability of Chitosan to prevent the absorption of enough dietary fat to affect energy balance in humans had not been substantiated. Because of this and the product's name, the Authority asked the advertisers both to make clear in future that the product had not been proven to aid slimming or prevent weight gain and to consult the Copy Advice team before advertising the product again. 
Three studies have found no significant differences in weight or serum cholesterol levels between subjects who took chitosan and those who received a placebo. One study involved 30 overweight volunteers who received four capsules of either chitosan or a placebo for 28 consecutive days and were told to eat their normal diet. The chitosan and placebo groups showed no differences in weight or serum cholesterol levels . The second study involved 51 healthy obese women followed for 8 weeks. The chitosan group had slightly (but not significantly) greater cholesterol reduction than the placebo group, but no difference in weight occurred between the two groups . The other study, which involved 68 obese men and women, found no improvement in weight, body composition, blood pressure, or lipid profile .
Another study has found that the amount of fat actually removed by chitosan is insignificant. The study involved 15 men who consumed five meals per day for 12 days with a daily total of about 25 grams of fat. The amount of fat excreted during four days when they took chitosan supplements was then compared to the amount excreted without chirosan. Taking 10 capsules of chitosan per day increased fecal fat excretion by only about 1 gram (9 calories), which would have no significant effect on a person's weight .
On August 31, 1999, the FDA warned the president of TRY-Lean, Inc., to stop making claims that taking his company's chitosan-containing products would reduce the risk of obesity, high blood pressure, heart attack, and cancer .
In 2000, the marketers of "The Enforma System" agreed to settle FTC charges of deceptively advertising that the user could "eat what you want and never, ever, ever have to diet again." The FTC complaint named Enforma Natural Products, Inc., its president and chief executive officer, Andrew Grey, and Fred Zinos, a former vice president of sales and marketing. The system consists of "Fat Trapper," a chitosan-based product purported to prevent the absorption of dietary fat; and "Exercise In A Bottle," a pyruvate product that supposedly increases the body's capacity to burn fat. The system was promoted chiefly through televised 30-minute infomercials, featuring former baseball player Steve Garvey, as well as through the company's Web site. The settlement prohibits the marketers from making unsubstantiated claims that any product, service, or program: provides weight control without dieting or exercise; prevents fat absorption; increases metabolism; burns fat; or allows weight loss even if users eat high-fat foods. The company must also pay $10 million to be used for refunds or distributed to the U.S. Treasury .