Medicinal Mushrooms as Modulators of Gut Microbiota, Intestinal Barrier Integrity and the Gut–Brain Axis: A Narrative Review

Abstract Background The gut microbiota plays a significant role in maintaining host homeostasis by influencing metabolism, immune system function, and bidirectional communication within the gut–brain axis. Numerous studies have demonstrated a correlation between alterations in microbial composition and activity, and the development of various chronic diseases, including obesity, type 2 diabetes mellitus, inflammatory bowel diseases, and neurodegenerative disorders. In recent years, there has been a surge of scientific interest in medicinal mushrooms, particularly as natural modulators of the gut microbiota and its metabolites. Objective The objective of this review was to analyse current evidence regarding the effects of selected medicinal mushrooms– Hericium erinaceus, Ganoderma lucidum, Cordyceps militaris, and Phellinus linteus –on gut microbiota composition, intestinal barrier function, and mechanisms associated with the gut–brain axis. Materials and Methods A narrative literature review was conducted, encompassing in vivo experimental studies, in vitro investigations, and available clinical studies evaluating the effects of the analysed mushroom species on gut microbiota composition, short-chain fatty acid (SCFA) production, inflammatory markers, and metabolic and neurological outcomes. Results All the analysed species of mushrooms demonstrated the ability to modulate the composition of the gut microbiota. The most frequently reported findings included an increased abundance of bacterial taxa considered beneficial to host health, such as members of the genera Lactobacillus, Bacteroides, Roseburia, Blautia, and Akkermansia, accompanied by a reduction in microorganisms associated with dysbiosis and inflammation. These microbial alterations were associated with enhanced production of short-chain fatty acids, particularly butyrate and propionate, improved intestinal barrier integrity, and reduced concentrations of inflammatory markers, including TNF-α, IL-1β, IL-6, and bacterial lipopolysaccharide (LPS). The most convincing evidence regarding the modulation of the gut–brain axis was reported for Hericium erinaceus, whose supplementation was associated with improved cognitive performance, attenuation of neuroinflammation, and favourable changes in gut microbial composition. It is evident that Ganoderma lucidum has demonstrated significant anti-inflammatory and metabolic effects, resulting in a reduction of metabolic endotoxemia and an improvement in obesity- and insulin resistance-related parameters. Cordyceps militaris has been demonstrated to have a positive influence on intestinal barrier integrity, immune regulation, and glucose metabolism. In contrast, Phellinus linteus polysaccharides have been shown to have considerable prebiotic potential, as evidenced by their ability to enhance SCFA production and improve metabolic outcomes in experimental models of type 2 diabetes. Conclusions Medicinal mushrooms represent a promising group of natural modulators of the gut microbiota and gut–brain axis-related processes. Their biological effects include regulation of microbial composition, enhancement of beneficial microbial metabolites, improvement of intestinal barrier function, and attenuation of chronic inflammation. The most significant scientific evidence currently available supports the effects of Hericium erinaceus and Ganoderma lucidum. Despite these encouraging findings, the majority of available data originate from preclinical studies, highlighting the need for well-designed clinical trials to determine the efficacy and safety of medicinal mushroom supplementation in humans.