The Role of the Gastrointestinal Microbiota in Parkinson’s Disease

Background/Objectives: Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons leading to debilitating motor and non-motor symptoms. Beyond its well-known neurological features, emerging evidence underscores the pivotal role of the gut–brain axis and gastrointestinal microbiota in PD pathogenesis. Dysbiosis has been strongly linked to PD and is associated with increased intestinal permeability, chronic inflammation, and the production of neurotoxic metabolites that may exacerbate neuronal damage. Methods: This review delves into the complex interplay between PD and dysbiosis, shedding light on two peculiar subsets of dysbiosis, Helicobacter pylori infection and small-intestinal bacterial overgrowth. These conditions may not only contribute to PD progression but also influence therapeutic responses such as L-dopa efficacy. Conclusions: The potential to modulate gut microbiota through probiotics, prebiotics, and synbiotics; fecal microbiota transplantation; and antibiotics represents a promising frontier for innovative PD treatments. Despite this potential, the current evidence is limited by small sample sizes and methodological variability across studies. Rigorous, large-scale, randomized placebo-controlled trials with standardized treatments in terms of composition, dosage, and duration are urgently needed to validate these findings and pave the way for microbiota-based therapeutic strategies in PD management.