How can chitosan work as a fat-blocker?
Today, application as a dietary fat blocker is the largest market for chitosan. Due to the hydrophobic character of the N-acetylglucosamine units, chitosan can effectively bind hydrophobic substances such as oil and fat. When e.g. olive oil is added to a glass of water, the oil will not mix with the water but form a layer on top of the water. If chitosan is added and mixed in, it will flocculate the olive oil which can thus easily be separated from the water. Chitosan ingested before a heavy meal is supposed to similarly bind fat and cholesterol, preventing it from being absorbed in the intestines. Even disregarding the fact that there is no scientific evidence for the effectiveness of the method (in fact, large meta-studies clearly show that there is no such effect), the amount of chitosan required to bind the amount of fat present in a high-fat meal is likely to cause at least indigestion. However, the fact that millions of people, in particular in the US and Asia, but also in Europe, have swallowed chitosan capsules for decades without any known negative side effects may be regarded as a large scale field experiment showing that chitosan is non-toxic at reasonably low doses (the amount typically recommended is around 1-2 grams per meal).