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

• Dietitian-Guided Nutritional Intervention (Behavioral), also known as Diet plan: Participants receive a diet plan and nutritional counseling provided by a registered dietitian, based on a standardized protocol aligned with the Dietary Reference Intakes (DRIs) and adapted for the management of Parkinson's disease and constipation. The intervention includes follow-ups with the dietitian over a 3-month period.

Primary outcomes

• Change in weekly bowel movement frequency [Baseline and 90 days]: Mean change in the number of spontaneous bowel movements per week from baseline to 12 weeks, based on participant-reported bowel diaries.

Secondary outcomes

• Change in relative abundance of gut microbial taxa [Baseline and 90 days]: Change in the relative abundance of selected bacterial genera associated with constipation and Parkinson's disease, measured by 16S rRNA sequencing of stool samples.

Other outcomes

• Change in dietary intake [Baseline, 45 days and 90 days]: Variation in intake of macronutrients and fiber, assessed through 24h food records.

Sex: All, ages: 18 Years to any

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

• National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Committee on the Dietary Reference Intakes for Energy. Dietary Reference Intakes for Energy. Washington (DC): National Academies Press (US); 2023 Jan 17. Available from http://www.ncbi.nlm.nih.gov/books/NBK588659/ PMID 36693139
• Barichella M, Cereda E, Cassani E, Pinelli G, Iorio L, Ferri V, Privitera G, Pasqua M, Valentino A, Monajemi F, Caronni S, Lignola C, Pusani C, Bolliri C, Faierman SA, Lubisco A, Frazzitta G, Petroni ML, Pezzoli G. Dietary habits and neurological features of Parkinson's disease patients: Implications for practice. Clin Nutr. 2017 Aug;36(4):1054-1061. doi: 10.1016/j.clnu.2016.06.020. Epub 2016 Jul 5. PMID 27406858
• Drossman DA, Hasler WL. Rome IV-Functional GI Disorders: Disorders of Gut-Brain Interaction. Gastroenterology. 2016 May;150(6):1257-61. doi: 10.1053/j.gastro.2016.03.035. No abstract available. PMID 27147121
• Postuma RB, Berg D, Stern M, Poewe W, Olanow CW, Oertel W, Obeso J, Marek K, Litvan I, Lang AE, Halliday G, Goetz CG, Gasser T, Dubois B, Chan P, Bloem BR, Adler CH, Deuschl G. MDS clinical diagnostic criteria for Parkinson's disease. Mov Disord. 2015 Oct;30(12):1591-601. doi: 10.1002/mds.26424. PMID 26474316
• Results publication: Brendler JH, da Silva KY, Dall'Alba V, Martins AF, Teixeira-Dos-Santos D, Schuh AFS, Olchik MR. Dietitian-led intervention to manage constipation in Parkinson's disease: Study protocol for a parallel-group randomized controlled trial (NUTRI-GUT-PD). PLoS One. 2026 Jul 27;21(7):e0354608. doi: 10.1371/journal.pone.0354608. eCollection 2026. PMID 42507749

• Maira Rozenfeld Olchik, PhD, Principal investigator, Federal University of Rio Grande do Sul