Effect of a Mediterranean diet intervention on gastrointestinal function in Parkinson's disease (the MEDI-PD study): study protocol for a randomised controlled trial

Introduction: Constipation is a common and sometimes debilitating non-motor symptom of Parkinson's disease (PD) that can result in intestinal inflammation and microbial dysbiosis. The Mediterranean diet, rich in fermentable fibres and anti-inflammatory phenolic compounds, is associated with reduced risk of developing PD and slower progression of parkinsonism. The Mediterranean diet is often recommended for people with PD; however, no studies to date examine this diet as a therapeutic intervention to modulate gastrointestinal (GI) dysfunction.

Methods and analysis: This is a randomised, controlled, parallel study. During a 2-week run-in, participants with PD and constipation symptoms (n=52) will undergo baseline nutritional and neurological assessments and provide a stool sample. Participants will be stratified by sex and Hoehn and Yahr stage and randomised to follow standard of care for constipation (control) or standard of care plus a Mediterranean diet (intervention) for 8 weeks. A study dietitian will provide dietary instruction and weekly follow-up via telephone to both groups to support adherence and monitor adverse events. Questionnaires will assess dietary intake and GI function including stool frequency, form, symptoms and laxative usage. Measurements completed at baseline will be repeated at 4 and 8 weeks of the intervention. The primary outcome is to evaluate the difference between mean change (final-baseline) in Gastrointestinal Symptom Rating Scale (GSRS) constipation syndrome scores for the control versus intervention groups. Secondary outcomes will assess stool frequency and form, weekly GSRS syndrome scores, digestive quality of life, laxative usage, faecal microbial communities and inflammatory markers, anxiety, depression, quality life, body weight and composition, dietary fibre intake and Mediterranean diet adherence.

Ethics and dissemination: The study has received University of Florida Institutional Review Board-01 approval (IRB202001333). Findings will be disseminated via conference presentations, lectures and peer-reviewed publications.

Trial registration number: NCT04683900.