This study will evaluate the safety and tolerability of a dietary fiber, resistant maltodextrin, in people with Parkinson's disease. It will also evaluate the fiber's effect on the gut microbiome and potential effects on motor function and non-motor functions. Half of the participants will receive resistant maltodextrin and the other half will receive a control substance, maltodextrin.

Intestinal microbiota may play in important role in Parkinson's disease (PD). Colonic bacteria play roles in multiple functions including gut motility and secretion of metabolites which can have systemic effects on the body. Recent evidence has shown that people with PD have an altered distribution of gut bacteria that healthy controls. These changes are associated with differences in various metabolites, including butyrate, that are involved in maintaining the gut barrier integrity and even gait and balance function. Microbiota dysbiosis could potentially exacerbate or even contribute to the pathogenesis of PD. Probiotic and dietary interventions may improve gut function and the motor symptoms in PD, but neither have been examined for their effect on the gut microbiome. Prebiotic treatments have been shown to order the microbiome in some populations, but have not been assessed for tolerability or efficacy in PD.

The objective of this study is to examine the safety and tolerability of resistant maltodextrin (RM), a prebiotic non-digestible fiber, and its effect on the microbiome and motor in non-motor symptoms and PD. The investigators will conduct a randomized, parallel-group double-blinded controlled trial assessing RM 50 g daily compared to maltodextrin (an easily digestible glucose polysaccharide) over 4 weeks. Patients will be dosed with 25 g daily for 1 week and then titrated to 50 g daily for the remaining 3 weeks.

The goals of this study include: 1) To determine the safety and tolerability of RM compared to maltodextrin in patients with PD; 2) To determine if RM will remodel the gut microbiome in patients with PD; 3) (exploratory) To determine if RM administration will improve motor and non-motor symptoms in PD.

Inclusion Criteria:

• Men and women age ≥60 years
• Diagnosis of PD based on United Kingdom PD brain bank criteria, Hoehn and Yahr stage 1-3.
• Stable dose of PD medications for 30 days prior to study and for duration of study
• If used, stable dose of melatonin, sedative/hypnotic or stimulant medications

Exclusion Criteria:

• use of other prebiotic or probiotic treatment for 30 days prior to or during the study
• unstable medical or psychiatric disorder
• history of diabetes mellitus or current use of medication for diabetes
• cognitive impairment based on Montreal Cognitive Assessment (MoCA) <25.
• current or recent (within previous 3 weeks) use of laxatives
• use of antibiotics in the past 30 days
• participation in another clinical trial in the past 30 days.

participants will be blinded to condition. control condition (maltodextrin) will be used and has identical appearance.

investigator and research staff (except pharmacy) will be blinded to condition