Constipation is a highly prevalent non-motor symptom in Parkinson’s Disease (PD), affecting a large proportion of patients and reducing quality of life. It is associated with prolonged intestinal transit, changes in gut motility, and gut microbiota alterations including loss of short-chain fatty acid–producing bacteria and enrichment of pro-inflammatory taxa. These gut changes have been linked to increased intestinal permeability and systemic inflammation, with potential implications for PD pathophysiology. Despite this, international guidelines lack a standardized approach for constipation management in PD; usual care commonly includes brief advice on fiber and lifestyle or the use of laxatives.
Dietary management is a promising non-pharmacological approach, but current evidence in PD is limited and heterogeneous. Dietary changes without expert oversight may risk weight loss, malnutrition, and sarcopenia. Nutritional interventions delivered by a dietitian have shown benefits in other contexts, improving diet quality and nutritional status. The NUTRI-GUT-PD protocol was developed to test whether individualized, dietitian-led nutritional counseling is superior to usual care in improving constipation in people with PD.
The trial will recruit outpatients with a prior diagnosis of PD confirmed by a neurologist according to Movement Disorders Society clinical diagnostic criteria. Eligible participants must be adults without dementia, report constipation meeting Rome IV criteria for functional constipation, and be on a stable dose of levodopa for at least three months. Exclusion criteria noted in the protocol include atypical or secondary parkinsonism, Hoehn & Yahr stage greater than 3, severe neurological or psychiatric conditions interfering with participation, and dementia. Recruitment will take place at the Movement Disorders Research Group outpatient clinic of the Hospital de Clínicas de Porto Alegre (HCPA), Brazil.
NUTRI-GUT-PD is a randomized, controlled, superiority trial with a parallel-group design and 90-day follow-up. The target sample size is 54 participants. After baseline assessments, participants are randomly allocated to either the intervention group (dietitian-led nutritional counseling) or the control group (usual care). The protocol follows SPIRIT reporting guidelines. Trial registration number is NCT07213856.
At baseline the following assessments are performed:
All baseline assessments are repeated at the 90-day endpoint to evaluate changes over the intervention period.
Participants randomized to the intervention group receive individualized nutritional counseling delivered by a dietitian over 90 days. The intervention combines one in-person consultation with bi-weekly follow-up phone calls. Counseling focuses on four main topics: healthy eating, food processing (choices regarding degree of processing), fiber and fluid intake, and interactions between diet and levodopa. Each participant in the intervention arm also receives an individualized diet plan tailored to their needs. The protocol specifies these elements but does not report treatment manuals or exact content in the summary; such operational details are part of the study materials.
Participants in the control group receive usual care as practiced in the clinical setting. Usual care typically consists of general advice on fiber intake and lifestyle modifications from the clinician or the use of laxatives. The protocol contrasts this standard approach with the structured, dietitian-led counseling in the intervention arm.
The primary outcome is the change in weekly bowel movement frequency from baseline to day 90 measured via the stool diary. Secondary outcomes include:
These outcomes aim to capture symptomatic, microbiological, dietary, and nutritional effects of the intervention.
The protocol specifies enrollment of 54 participants in total. As a study protocol, no datasets have yet been generated or analyzed; the authors state that all relevant data will be made available upon study completion in line with PLOS guidelines for study protocols. The trial is registered under NCT07213856.
The study received funding support in part from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) as doctoral scholarship support. The funder had no role in study design, data collection, analysis, interpretation, decision to publish, or manuscript preparation according to the protocol. The authors declared no competing interests in the manuscript. The protocol was prepared following SPIRIT guidance and includes ethical and logistical considerations appropriate for a single-center randomized trial.
The protocol frames constipation in PD as a common, impactful non-motor symptom with mechanistic links to gut dysbiosis and possible relevance to disease progression. The investigators propose that a structured, individualized dietitian-led intervention could offer superior control of constipation symptoms and beneficial shifts in gut microbiota and diet quality compared with usual care. The protocol notes gaps in current evidence for dietary management in PD, limited prior RCT data, and concerns that unguided dietary change may pose nutritional risks.
As a study protocol, the manuscript does not report trial results. Specific procedural details such as randomization method, allocation concealment, blinding procedures, statistical analysis plans, and exact sample size calculation parameters are described in the full protocol but are not detailed in this summary. Data and outcomes will be reported after study completion and analysis as per trial registration and PLOS data availability statements.
Overall, NUTRI-GUT-PD tests a pragmatic, dietitian-delivered approach to a frequent and under-treated symptom in PD, with prespecified clinical, dietary, and microbiota endpoints to assess potential symptomatic and mechanistic benefits.