Nutritional Intervention for Constipation Symptoms in Patients With Parkinson's Disease

The goal of this clinical trial is to evaluate whether a dietitian-guided nutritional intervention can improve constipation symptoms in people with Parkinson's disease (PD). The main questions it aims to answer are: * Can a dietitian-guided nutritional intervention increase the number of weekly bowel movements in individuals with PD and functional constipation? * Can this intervention positively influence gut microbiota composition, dietary intake, and nutritional status? Researchers will compare the intervention group to a control group that will receive general dietary guidance only after the study period, to see if the intervention leads to improvements in bowel function and related health outcomes. Participants will: * Follow a diet plan developed by a dietitian, based on dietary reference intakes and tailored to the needs of individuals with PD and constipation * Participate in follow-up sessions with the dietitian for 3 months * Complete assessments at baseline, midpoint, and end of the intervention to evaluate bowel function, constipation symptoms, gut microbiota, nutritional status, and diet quality

Inclusion Criteria: * Adults with a previous diagnosis of Parkinson's disease * On a stable dose of levodopa for at least 3 months * Diagnosis of Functional Constipation by the Rome IV protocol Exclusion Criteria: * Diagnosis of atypical or secondary parkinsonism * Hoehn and Yahr stage greater than 2 * Presence of severe neurological or psychiatric disorders that impair the ability to participate in study procedures * Previous diagnosis of dementia * Presence of comorbidities such as active cancer, chronic obstructive pulmonary disease (COPD), heart failure, and/or chronic kidney disease * History of gastrointestinal cancers, inflammatory bowel diseases, or surgeries involving the gastrointestinal tract * Constipation secondary to clinical conditions such as hypothyroidism or diabetes mellitus * Use of opioids * Use of probiotics or antibiotics in the past 8 weeks * Continuous use of laxatives in the past 8 weeks * Presence of severe dysphagia according to the Functional Oral Intake Scale (FOIS) * Individuals receiving enteral or parenteral nutrition * Individuals under nutritional follow-up in the past 3 months