Gut dysbiosis in Parkinson’s disease: A systematic review of human studies

Introduction: Parkinson’s disease (PD) is increasingly correlated to gastrointestinal disturbances and intestinal microbiota alterations. Growing evidence suggests that shifts in gut microbial communities may influence immune activation and metabolic pathways relevant to PD. Objective: This systematic review examines microbial changes in PD and their clinical relevance. Methods: A systematic search of PubMed, Scopus, and Web of Science identified 819 records. After removing duplicates and screening, 521 full-text articles were evaluated. Ten studies met the inclusion criteria, focusing on human subjects and original data on gut microbiota composition, function, or modulation in PD. Results: The microbiome profile most frequently reported in PD includes a drop in overall diversity and in bacterial taxa associated with short-chain fatty acid production, alongside a shift toward taxa commonly associated with inflammatory states (e.g., Enterobacteriaceae). Most studies reported associations between dysbiosis and motor severity, constipation, autonomic dysfunction, and neuropsychiatric symptoms. Interventions such as resistant starch supplementation and acupuncture improved microbial profiles and some clinical outcomes. Machine-learning approaches showed promising diagnostic potential based on microbial signatures. Conclusions: Gut dysbiosis is significantly associated with PD clinical features. Although early evidence suggests potential therapeutic and diagnostic applications, methodological heterogeneity and small sample sizes highlight the need for standardized, longitudinal research.