Supplements of chitosan, derived from the chitin naturally present in large quantities in shellfish, are marketed as a weight loss product as the fibre has been shown to bind fat in the intestine, blocking its absorption. Not all trials have however proven its efficacy in weight loss management.
The new study, published in the September issue of the International Journal of Obesity (28, 1149-1156), is one of the largest to date. The researchers assigned 250 adults, with an average body mass index of 35.5, to receive either 3g of chitosan daily or a placebo for 24 weeks. All participants received standardised dietary and lifestyle advice for weight loss.
The researchers from the Clinical Trials Research Unit in the University of Auckland report that the chitosan group lost more body weight than the placebo group "but the effects were small". The chitosan group lost an average of 0.4kg compared to a 0.2 kg gain in the placebo group.
Similar small changes were seen in the total and LDL cholesterol levels and there were no significant differences between groups for any of the other measured outcomes such as body mass index, waist circumference, body fat percentage, blood pressure or quality of life.
"We do not know of any limiting factors in our study that would haveprevented a greater effect on weight loss. Our trial was designed andanalysed according to international clinical trial standards and is thelargest trial of chitosan to date with the most outcome measures," Dr Cliona Ni Mhurchu, senior research fellow at the Clinical Trials Research Unit, told NutraIngredients.com.
She added: "It is unlikely that a longer follow-up period would change the outcome since it is common in weight loss studies to lose more weight in the earlier than in the later stages. Our dose is similar to that used in other studies and is greater than that advised by the manufacturer."
The product tested was a beta-chitosan supplement derived from New Zealand squid pens. It was 76% deacetylated and had a molecular weight of 130,000.
Previous trials of chitosan that found a large effect on body weight were of questionable quality, and some contained other weight loss agents in addition to chitosan, which may explain their effectiveness, added Dr Ni Mhurchu.
But James France, general manager of Wilkie Resources which markets the LipoSan Ultra brand chitosan in the US, noted that there are significant issues with bioavailability of chitosan, which could prevent some supplements from having a significant effect.
"Chitosan is a very large fibre that is difficult to get into a solution. Regular chitosan is so tightly bound that it does not dissolve enough in the stomach to allow it to interact with the fat."
The LipoSan Ultra chitosan has been modified using succinic acid which holds the fibre apart enough to allow it to dissolve, forming a gel with fat modules and binding them so that they move out of the gastrointestinal tract before being broken down by lipase.
The former manufacturer of LipoSan, Vanson Halosource, carried out a randomized, double-blind, placebo controlled clinical trial of chitosan for weight loss on 59 mildly obese women. After 8 weeks a statistically significant reduction in weight was seen in the chitosan group, showed the results, published in 2001.
"I don't refute their results [the New Zealand trial] but you need to look at how this particular product behaves," France told NutraIngredients.com.
He noted that the new LipoSan owner Primex was examining protocols for an additional study, which could offer further evidence to support the ingredient, now on the market for three years.
Primex claims to be the world's biggest supplier of chitosan products, with a market share in Europe and in Asia of around 50 per cent.