Mediterranean Diet Intervention to Improve Gastrointestinal Function in Parkinson's Disease a Randomized, Controlled, Clinical Trial

Inclusion Criteria: * Physician-diagnosed Parkinson's disease aged 40-85 years * Drug naïve or on stable dosage of Parkinson's medications with no plans to change for the duration of the study protocol * Hoehn \& Yahr stage =\<2.5 in the clinical "ON" state * Constipation syndrome scores \>=2.0 based on the GSRS * Consume \<20 grams of fiber daily based on the Block Fruit/Vegetable/Fiber screener * Able to complete informed consent in English * Willing to maintain habitual diet through the pre-baseline period. * Willing to make dietary changes to follow a Mediterranean diet and/or receive standard of care for constipation during the intervention period. * Willing to complete daily and weekly questionnaires and 12 dietary recalls over approximately 10 weeks. * Able to provide stool samples during the study collection periods. * Willing to avoid strenuous exercise and alcohol such as beer, wine, and cocktails 24 hours prior to each of the 3 study visits. * Able to fast (no food or drink, except water, or decaf tea) at least 12 hours before each study visit * Willing to discontinue taking prebiotic, herbal, or high-dose vitamin or mineral supplements that may impact inflammation during the pre-baseline period and throughout the study protocol. Exclusion Criteria: * Atypical or secondary Parkinsonism * Underweight (BMI \<18.5) * History of deep brain stimulation (DBS) surgery * Regular use of enemas or suppositories to alleviate constipation (e.g., \>1 time per week) * Use of another investigational product within 3 months of the screening visit * Antibiotic or probiotic supplement use within 2 months from the day of stool collection * Currently being treated for a physician-diagnosed GI disease or condition other than constipation, irritable bowel disease, gastroparesis, reflux or diverticular disease