Diets impact Parkinson's motor symptoms, supplements show no benefit, study finds

By Hugo Francisco de SouzaFeb 21 2024Reviewed by Susha Cheriyedath, M.Sc.

In a recent meta-analysis and systematic review published in the European Journal of Clinical Nutrition, researchers collated and reanalyzed data on the effects of diets (and, by extension, dietary patterns and supplements) in accelerating or attenuating Parkinson’s disease (PD). Their review and reassessment of data from 24 publications reveals that the Mediterranean, ketogenic, and other low-protein dietary regimes could effectively lower the total Unified Parkinson Disease Rating Scale (UPDRS) score, improving overall motor function. Contrary to prior hypotheses, however, dietary interventions, including supplementation, were not observed to improve UPDRS or six-min walk test (6MWT) distance scores.

Study: Effects of dietary supplements, foods, and dietary patterns in Parkinson’s disease: meta-analysis and systematic review of randomized and crossover studies. Image Credit: Chinnapong / Shutterstock

Neurodegenerative diseases and diets

Neurodegenerative diseases are age-related chronic non-transmissible conditions characterized by the loss of function of the peripheral nervous system or brain cells. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the two most prevalent examples of neurodegenerative diseases, with the latter affecting more than 1% of all humans above 60, making it the most common movement disorder in the world.

Unfortunately, as is the case for most neurodegenerative conditions, no cure for PD currently exists, with clinical interventions aimed at managing the condition and slowing its progress and research focused on PD prevention. The recent surge in PD incidence has been primarily attributed to the global evolution of dietary consumption and health behaviors, with suboptimal Western-style dietary regimes and sedentary lifestyles deemed the main culprits.

“A healthy diet, lifestyle enhancement, antioxidant agents, and nutrients targeting anti-inflammatory can be a potentially effective strategy for treating PD.”

A growing body of scientific evidence suggests the profound association between dietary choices and age-related clinical outcomes, with some diets observed to accelerate the onset and progression of PD while others reduce the risk of acquiring the disease. Despite many randomized controlled trials (RCTs) and crossover studies revealing the dietary benefits, primarily related to the gut microbiome, of maintaining healthy diets, reviews and meta-analyses discussing their findings and consolidating their results remain severely lacking.

About the study

The present study is registered with the International Prospective Register of Systematic Reviews (PROSPERO) database, and its methodologies were designed to comply with both the Cochrane Handbook for Systematic Reviews of Interventions and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data for the study was collated from eight online scientific publication repositories, namely PubMed, Embase, Medline, Cochrane Library, SCOPUS, Wanfang, China National Knowledge Infrastructure (CNKI), and Weipu, from database initiation till June 26, 2022.

Study inclusion criteria comprised study type (randomized controlled trial [RCTs]), language (English), study interventions, clinically confirmed PD, and results reported as Unified Parkinson Disease Rating Scale (UPDRS) or International Parkinson and Movement Disorder Society UPDRS (MDS-UPDRS) total score, UPDRS or MDS-UPDRS motor score, six-min walk test (6MWT), or quantitative insulin sensitivity check index (QUICKI).

Publication selection comprised title, abstract, and full-text screening phases, with in vitro experiments excluded from the analyses. Data extraction included study characteristics, patient sample size, dietary interventions (including intervention durations), and results. The Cochrane Risk of Bias instrument for randomized trials version 2 (ROB2) was used to assess included publications for bias risk across all five of its recommended parameters. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool was additionally used to evaluate data quality and effectiveness.

Mean differences (MDs) and standard deviations (SDs) were used to standardize results for meta-analyses conducted in the Cochrane Collaboration’s Review Manager 5.4 software. I² was computed to evaluate the degree of discrepancy between studies and the Chi-square test to estimate between-test heterogeneity. Finally, sensitivity analyses were carried out to assess potential publication bias.

Study findings

Initial database screening revealed 9,970 studies titles pertaining to the topic, 291 of which were duplicates. Abstract screening narrowed down the list to 28, which full-text screening further shortened to the final set of 24 publications.

Results of the present meta-analyses elucidate that while QUICKI indices depict improvements following dietary supplementation, UPDRS (and its derivatives) and 6MWT scores show no such improvements. In contrast, systematic review findings suggest that some nutritional regimes, particularly the Mediterranean diet, ketogenic diets, and other diets featuring low-protein intakes, significantly lowered UPDRS scores and mitigated motor PD symptoms.

“In the future, it is necessary to conduct a studies sample size with sufficient power to evaluate how different kinds of dietary intervention affect people with PD.”