Fungal Polysaccharides Show Promise as Prebiotics for Gut Health

Scientists have spent decades learning that the trillions of microorganisms living in your gut do far more than digest food. They influence how your body processes glucose and fat, shape your immune response, and maintain the barrier that keeps the intestinal wall intact. When that microbial balance tips—a condition researchers call dysbiosis—chronic diseases often follow: type 2 diabetes, obesity, inflammatory bowel disease. The question has become urgent: can we deliberately feed the right bacteria to restore health?

A new systematic review, published in npj Science of Food, examined 20 species of edible and medicinal fungi to see whether their polysaccharides—complex carbohydrates made from chains of simple sugars—might work as prebiotics, essentially fertilizer for beneficial gut bacteria. The researchers found something promising: these fungal compounds have a structural trick that makes them useful. Human digestive enzymes cannot fully break them down as they pass through the stomach and small intestine. Instead, they arrive intact in the colon, where the resident bacteria ferment them, producing short-chain fatty acids like butyrate and propionate—molecules linked to better metabolic health and a stronger intestinal barrier.

The fungi examined included species with names familiar to anyone who has bought mushrooms at a market or explored traditional medicine: reishi (Ganoderma lucidum), shiitake (Lentinus edodes), and cordyceps (Cordyceps militaris), among others. Ninety-five percent of the species studied belonged to the class Agaricomycetes, with the Polyporaceae family alone accounting for 15 percent. The polysaccharides themselves varied enormously in size, ranging from a few thousand to several million daltons, and in their chemical composition. Some contained glucose, others galactose, mannose, xylose, or fucose. But the review suggested something counterintuitive: the way these sugar units link together may matter more than which sugars are present.

Extraction method proved crucial. Researchers compared hot-water extraction, enzymatic methods, and other techniques, finding that how you pull the polysaccharides from the fungus affects not just how much you get but also the molecular size and structure of what you extract. Combining methods tailored to each fungal species might yield better results than any single approach.

Across the reviewed studies, fungal polysaccharides altered the composition of gut bacteria in measurable ways. Some interventions increased beneficial species like Bifidobacterium and Lactobacillus while reducing potentially harmful bacteria such as Desulfovibrio. The fermentation of these compounds produced higher levels of short-chain fatty acids. In various experimental models, researchers also observed increases in HDL cholesterol (the protective kind), reductions in total cholesterol and triglycerides, lower levels of lipopolysaccharide (a bacterial molecule associated with inflammation), and increases in proteins that help maintain intestinal barrier integrity.

The evidence pointing toward benefits for colitis, type 2 diabetes, and obesity is real but comes almost entirely from laboratory dishes and animal studies. No human clinical trials have yet tested whether eating mushroom polysaccharides actually produces these effects in people. The review's authors were clear on this limitation: before these findings can guide dietary recommendations or inform treatment decisions, researchers need to move from the controlled environment of the lab into human bodies, where variables multiply and individual differences matter enormously. The promise is there. The proof, for now, remains ahead.