The Effect of the Mediterranean Diet on Gut Microbiota and Its Impact on Neurodegenerative Diseases: A Narrative Review

Abstract: Due to their complex etiology and the intricacy of brain systems, neurodegenerative diseases (NDs), which progressively deteriorate neural tissue, remain difficult to treat. The gut-brain axis emphasizes the host–gut microbiota (GM) interaction and offers a new perspective on these diseases. In Alzheimer’s disease (AD), there is a hypothesis of the migration of amyloid-β oligomers from the gut to the brain may affect neuroinflammation. Also, in Parkinson’s disease (PD), GM in the gastrointestinal mucosal layer may misfold and accumulate α-synuclein, leading to its transfer to the brain. Multiple Sclerosis (MS) is affected by GM that influences immune responses toward inflammation through modulation of T-helper cell polarization, T-regulatory (T-reg) cell function, and B-cell activity. Furthermore, neuromyelitis optica spectrum disorder (NMOSD) is linked to antibodies that target the astrocyte-expressed water channel protein aquaporin-4 (AQP4) and may be related to GM and needs more research. Diet is a major factor that could modulate GM composition. The Mediterranean Diet (MD) is anti-inflammatory, antioxidant, and gut-modulating due to its high vegetable, fruit, whole grain, and olive oil intake. It boosts beneficial GM and their byproducts, which suppresses inflammation and may slowing progression and improve PD, AD, MS, and NMOSD, influencing disease progression and symptoms. This review aims to investigate the interaction between GM composition and the MD and how they jointly influence neurodegenerative diseases such as AD, PD, MS, and NMOSD. Keywords: alzheimer disease, parkinson disease, multiple sclerosis, neuro myelitis optica spectrum disease, gut microbiota, Mediterranean diet