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