The Gut–Brain Axis and Neurodegenerative Diseases: The Role of Nutritional Interventions Targeting the Gut Microbiome—A Systematic Review

The gut–brain axis (GBA) comprises bidirectional communication connecting the gut and brain. Many neurodegenerative disorders (NDDs), such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple sclerosis (MS), are characterized by a dysfunction of the GBA, indicating its possible role in disease pathogenesis. This systematic review was performed according to PRISMA guidelines, mainly using the following keywords: gut–brain axis, gut microbiota, gut dysbiosis, neurodegenerative disorders, prebiotics, and probiotics. The most recent scientific articles were searched from the PubMed, Google Scholar, and Scopus databases. The main components and communication pathways of the GBA are discussed in this study, and the aim was to investigate if therapeutic approaches, through dietary intervention targeting the gut microbiota, could ameliorate NDDs. The gut microbiota is a crucial constituent of the GBA, and an unbalanced microbiota, known as dysbiosis, has been related to GBA impairment and neurodegeneration. In most of the studies discussed, the modulation of the microbial constitution through nutritional intervention and probiotic and prebiotic supplementation showed promising outcomes. Although promising, further research is essential to fully elucidate the mechanisms involved and confirm the therapeutic potential of gut microbiota modulation in NDDs.