Everyone will remember Chitosan and the fashion of ten years ago or more, when this natural substance was marketed for aesthetic purposes. Chitosan derives from chitin, a natural polymer that is very abundant in nature, second in abundance only to the cellulose of plants and trees. It is the main component of the exoskeleton of insects, molluscs and marine crustaceans. By treatment with sulfuric acid in controlled conditions, chitin is transformed into chitosan which, unlike the parent substance (insoluble), is soluble in water and other aqueous solvents. As a substance with a sequestering action on various organic compounds, chitosan was advertised and sold for its presumed ability to remove cholesterol, triglycerides and excess starches, food substances whose excessive intake is linked to metabolic disorders such as obesity, hypercholesterolemia, diabetes and steatosis hepatic. Vegetable glucans extracted from food sources such as mushrooms, oats, barley and others have a similar action.
According to a latest study conducted on mice by the Washington University School of Medicine in St. Louis and published in the famous journal Science, researchers led by Steven Van Dyken, PhD, associate professor of Pathology and Immunology, have discovered in mice that digesting chitin activates the immune system. An active immune response has been linked to less weight gain, reduced body fat, and resistance to obesity. The researchers found that a particular arm of the immune system is also involved in the digestion of chitin. Distension of the stomach after ingesting chitin activates an innate immune response that stimulates stomach cells to increase the production of enzymes, known as chitinases, that break down chitin. Note that chitin is insoluble – incapable of being dissolved in a liquid – and therefore requires enzymes and harsh acidic conditions to digest, as mentioned above. The central point is that the pancreatic digestive system does not possess enzymes capable of digesting this substance.
The scientists performed the experiments on germ-free mice that lacked intestinal bacteria. The results show that chitin activates immune responses in the absence of bacteria. So they reasoned that chitin digestion relied primarily on host chitinases. Stomach cells change their enzyme production through a process we call adaptation. But it is surprising that this process occurs without microbial input, because bacteria in the gastrointestinal tract are also sources of chitinases that degrade chitin. The researchers noted that in mice with gut bacteria, dietary chitin altered bacterial composition in the lower gastrointestinal tract, suggesting that gut bacteria also adapt to chitin-containing food after it leaves the stomach. They also found that the greatest impact on obesity in mice occurred when chitin activated the immune system but was not digested. Mice fed a high-fat diet were also given chitin. Some mice lacked the ability to produce chitinase to break down chitin.
Mice that ate chitin but could not break it down gained less weight, had lower body fat measurements, and resisted obesity, compared to mice that did not eat chitin and those that ate it but could break it down. If the mice could break down the chitin, they would still benefit metabolically, but they would have adapted by overproducing chitinase to extract nutrients from the chitin. Chitin is nothing more than a resistant polymer of N-acetyl-glucosamine, a substance that is part of the composition of many glycoproteins (including antibodies), cellular receptors, antigens and adhesion molecules (integrins, cadherins, etc.). Furthermore, as glucosamine, it is a fundamental constituent of the cartilage matrix (glycans, hyaluronic acid, chondroitin, etc.). Therefore this study does not only open the door to the fight against obesity or diabetes, but also to the possibility of using dietary chitin (with that “adaptation” process mentioned above) to supply glucosamine.
As a monosaccharide, in fact, both glucosamine and N-acetyl-glucosamine are not found free at all in the plant or animal kingdom and their integration occurs with dedicated supplements; especially as a complement for osteoarthritis, rheumatoid arthritis, osteoporosis and post-traumatic arthritis. Being able to obtain this substance from a regular diet could also represent an advantage for the complementary management of these widespread rheumatological conditions.
by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific publications
Kim DH, Wang J et al. Science 2023 Sept; 381(6662):1092.
Ranaivo H, Zhang Z et al. Sci Rep. 2022 May 25; 12(1):8830.
Chen TC, Ho YY, Tang RC et al. Nutrients. 2021; 13(12):4405.