Clinical Significance of Intestinal Fungal Overgrowth: Integrating the Gut Mycobiome into Modern Gastroenterology

Intestinal fungal overgrowth (IFO) is an increasingly recognized yet underexplored component of gut dysbiosis with potential implications for gastrointestinal and systemic disease. While bacterial microbiota have historically garnered research attention, recent advances in sequencing technologies have highlighted the importance of the gut mycobiome in maintaining intestinal homeostasis. Disruption of fungal–bacterial balance, particularly involving Candida albicans, C. tropicalis, and C. glabrata, may contribute to symptom generation through immune activation, epithelial barrier dysfunction, biofilm formation, and the production of toxic metabolites such as acetaldehyde and candidalysin. Emerging clinical evidence suggests that IFO is associated with persistent gastrointestinal symptoms, including bloating, abdominal discomfort, and altered bowel habits, particularly in patients who do not respond to conventional therapies targeting bacterial overgrowth. Furthermore, fungal dysbiosis involving Malassezia restricta and Saccharomyces cerevisiae has been associated with inflammatory bowel disease, metabolic disorders, and systemic immune dysregulation; however, the nature and directionality of these relationships remain incompletely understood. Despite increasing recognition, the diagnosis of IFO remains challenging due to a lack of standardized criteria and validated non-invasive tools. Therapeutic strategies, including antifungal agents such as fluconazole and nystatin, as well as microbiome-targeted interventions, show promise but require further validation. This review provides a comprehensive synthesis of current evidence regarding the epidemiology, pathophysiology, clinical manifestations, diagnostic challenges, and therapeutic implications of IFO, with particular emphasis on species-specific mechanisms. Recognition of the intestinal mycobiome as a potentially important component of gut health may provide new perspectives for understanding gastrointestinal disorders and inform future precision medicine approaches.