Mediterranean Diet Adherence, Gut Microbiota and Parkinson's Disease: A Systematic Review

Background: There is mounting evidence to suggest that high adherence to the Mediterranean diet (MedDiet) may reduce the risk of age-related diseases, including Parkinson's disease (PD). However, evidence for the role of the MedDiet in the relief of motor and non-motor symptoms in patients with PD remains limited and inconclusive. We provide a systematic review of the effects of the MedDiet on the clinical features of PD using data from randomised controlled trials (RCT) and prospective observational studies. Methods: We searched MEDLINE, EMCare, EMBASE, Scopus and PubMed from inception until June 2023. Reference lists and the grey literature were also searched. Human studies with no restriction on language or publication date, examining associations between MedDiet adherence and the symptoms of PD, were included. We employed standard methodological procedures for data extraction and evidence synthesis and used the Quality Criteria Checklist for assessing the studies included. Results: Four studies from three unique cohorts, including two observational studies (n = 1213) and one RCT (n = 70), met the inclusion criteria. Despite the short study duration reported in all included reports, high MedDiet adherence was associated with changes in the gut microbiota (e.g., increased abundance of short-chain fatty acids producers). These outcomes correlated with a significant improvement in several non-motor symptoms including cognitive dysfunction, dyspepsia and constipation. However, there were no significant changes in diarrhoea, gastrointestinal reflux, abdominal pain and motor symptoms. Conclusion: High MedDiet adherence may be associated with significant improvement in global cognition and several gastrointestinal symptoms, possibly associated to changes in gut microbiota composition. Further studies are warranted to clarify potential cause-and-effect relationships and to elucidate MedDiet impact on motor symptoms.