Abstract: A mushroom blend comprises therapeutically effective amounts of the isolated strains Grifola frondosa (GF AM-P36), Ganoderma lucidum (GL AM-P38), and Pleurotus ostreatus (PO AM-GP37). Methods of use for supporting gut health include increasing SCFAs including butyrate in the gastrointestinal tract. A method is described for increasing microbial diversity in the gastro-intestinal tract in a human subject, including administering to the human subject an effective amount of a fungal prebiotic-containing composition comprising a blend of more than one fungal species. One useful blend of three species includes Ganoderma lucidum (“GL”), Grifola frondosa (GF), and Pleurotus ostreatus (PO). Operational Taxonomic Units (OTUs) including Lachnospiraceae, Lachnoclostridium and the various Ruminococcaceae are all dose-dependently increased when the mushroom blend is fed, which is significant for Lachnospiraceae UCG-004, Ruminococcaceae UCG-002, and Ruminococcaceae NK4A214.