The Gut Microbiota as a Mediator of the Metabolic Benefits of Fungi and Their Polysaccharides: A Review of Evidence Addressing Causality

Prebiotic supplementation has emerged as a promising strategy to ameliorate metabolic disorders through beneficial reshaping of the gut microbiota. Accumulating evidence suggests that fungi and their polysaccharides (e.g., those from Auricularia auricula-judae, Boletus edulis, Hirsutella sinensis, Isaria cicadae, Ramaria botrytoides, and Wolfiporia cocos) possess considerable potential in this context. The present review summarizes studies providing data relevant to the potential involvement of the gut microbiota in mediating the metabolic benefits of fungal interventions. Observed outcomes, potentially linked to the gut microbiota, included reductions in body, visceral fat, and liver weights, improved lipid and glycemic profiles, enhanced insulin sensitivity, and decreased circulating lipopolysaccharide, leptin, and proinflammatory cytokines (TNF-α, IL-1β, IL-6). Upregulation of tight junction proteins in the colon implied strengthened gut barrier function. Histological analyses revealed smaller adipocytes and attenuation of hepatic steatosis. Additional effects included stimulation of white adipose tissue browning and enhanced hepatic thermogenesis. Alterations in gut microbiota composition were diverse; however, a reduction in the Firmicutes/Bacteroidetes ratio was commonly reported. Furthermore, oral administration of bacterial species enriched by fungal interventions, such as Papillibacter cinnamivorans, Parabacteroides goldsteinii, Bacteroides intestinalis, Lactobacillus johnsonii, and Enterococcus casseliflavus, reproduced the metabolic improvements, supporting their possible mediating role. Collectively, current evidence indicates that fungi and their polysaccharides may exert metabolic benefits, at least in part, through gut microbiota modulation; however, further investigation is needed to determine the extent to which the gut microbiota contributes causally to these benefits.