Study in mice found that digesting #chitin, an abundant dietary fiber in insect exoskeletons & mushrooms & crustacean shells, engages the immune system. An active immune response was linked to less weight gain, reduced body fat & resistance to #obesity.
Editor’s summary
Chitin (β-1,4-poly-N-acetylglucosamine) is a highly abundant natural polysaccharide found in arthropods and fungi that can initiate type 2 (allergic) immune responses. Kim et al. report in mice that the consumption of chitin triggers gastric distension, downstream neuropeptide release, and type 2 cytokine production by tuft cells and type 2 innate lymphoid cells. This in turn drives gastrointestinal remodeling and the generation of acidic mammalian chitinase by chief cells, which is needed for chitin digestion. The addition of dietary chitin improved metabolic readouts in mice fed a high-fat diet, possibly because activated chief cells produce other digestive enzymes, including lipase. This mammalian adaptation to chitin may therefore serve as a potential therapeutic target for metabolic diseases such as obesity. —Seth Thomas Scanlon
Abstract
Dietary fiber improves metabolic health, but host-encoded mechanisms for digesting fibrous polysaccharides are unclear. In this work, we describe a mammalian adaptation to dietary chitin that is coordinated by gastric innate immune activation and acidic mammalian chitinase (AMCase). Chitin consumption causes gastric distension and cytokine production by stomach tuft cells and group 2 innate lymphoid cells (ILC2s) in mice, which drives the expansion of AMCase-expressing zymogenic chief cells that facilitate chitin digestion. Although chitin influences gut microbial composition, ILC2-mediated tissue adaptation and gastrointestinal responses are preserved in germ-free mice. In the absence of AMCase, sustained chitin intake leads to heightened basal type 2 immunity, reduced adiposity, and resistance to obesity. These data define an endogenous metabolic circuit that enables nutrient extraction from an insoluble dietary constituent by enhancing digestive function.
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