DOES IT WORK:CHITOSAN IS a dietary supplement promoted to help people lose weight. It is made from the powdered shells of marine shellfish and is one member of the chitin group of natural compounds, writes DÓNAL O'MATHÚNA
These are complex sugars, or polysaccharides, which are water-compatible and biodegradable. Chitosan is believed to bind to fat and other dietary components to prevent their digestion and absorption. Because of the worldwide problem with obesity, and its associated diseases and ill health, there is great interest in finding dietary supplements that might help people reduce their body weight.
Although there are pharmaceutical drugs that suppress appetite, these are expensive and tend to have side effects.
Evidence from studies
Early studies demonstrated that chitosan, when added to animal feed, bound dietary fat and led to the animals absorbing less fat.
Some studies also noted that the animals’ cholesterol levels were reduced. As a result of these studies, clinical trials were done in humans resulting in several publications over the past 10 years.
A Cochrane Collaboration systematic review was published in 2008 which looked at 15 randomised controlled trials.
These were conducted around the world, although close to half of them were carried out by one manufacturing company in Italy.
Although the individual trials varied in their details, they all compared chitosan with placebo for weight-loss. Overall, those taking chitosan lost an additional 2kg compared with those taking placebo.
But when only the highest quality trials were combined, the average weight-loss was only 0.6kg.
The average weight lost was also smaller in the trials that lasted longer. In trials that lasted up to four weeks, people lost an average of just over 2kg. However, in the trials that continued for longer than four weeks, the average weight-loss was 0.8kg.
Although these differences were statistically significant, the practical significance of such small amounts of weight-loss is questionable.
The finding that the longer studies resulted in less weight loss was also discouraging. While many weight-loss supplements and diets result in initial success, long-term benefits are much more difficult to obtain yet are vital to long-term health.
Some of the above trials also examined the impact of chitosan on serum cholesterol levels. The results were very similar to those with weight loss.
A statistically significant reduction in cholesterol levels was found, but the benefits were much smaller in the high-quality trials and those that lasted longer.
Problematic aspects
In the controlled trials, participants taking chitosan reported similar adverse effects to those taking placebos. Concerns have been expressed that chitosan may bind fat-soluble vitamins resulting in lower intakes that might require vitamin supplementation.
People with shellfish allergies should be cautious about chitosan, although such allergies are usually caused by components other than chitosan.
Only high-quality supplements should be used to avoid concerns about trace contaminants from the shells.
Recommendations
There is some evidence that chitosan may help reduce the amount of fat absorbed into the body from the diet and so help to reduce weight. It appears to have few adverse effects.
The evidence that chitosan lowers cholesterol levels is somewhat weaker. But the amount of weight lost or the reduction in cholesterol levels is very small.
Questions also remain about the quality of some of these trials and the way they have been reported.
Weight loss is a long-term challenge that requires lifestyle changes. Few studies have examined the effectiveness of chitosan for longer than four weeks.
Chitosan may provide some short-term help, but it cannot replace the two central pillars of weight loss: reducing energy intake through consuming fewer calories and increasing energy output through physical activity.
- Dónal O'Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University