In a recent meta-analysis and systematic review published within the European Journal of Clinical Nutrition, researchers collated and reanalyzed data on the results of diets (and, by extension, dietary patterns and supplements) in accelerating or attenuating Parkinson’s disease (PD). Their review and reassessment of information from 24 publications reveals that the Mediterranean, ketogenic, and other low-protein dietary regimes could effectively lower the full Unified Parkinson Disease Rating Scale (UPDRS) rating, improving overall motor function. Contrary to prior hypotheses, nevertheless, dietary interventions, including supplementation, weren’t observed to enhance 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 characterised by the lack of function of the peripheral nervous system or brain cells. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the 2 most prevalent examples of neurodegenerative diseases, with the latter affecting greater than 1% of all humans above 60, making it essentially the most common movement disorder on this planet.

Unfortunately, as is the case for many neurodegenerative conditions, no cure for PD currently exists, with clinical interventions aimed toward 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 worldwide evolution of dietary consumption and health behaviors, with suboptimal Western-style dietary regimes and sedentary lifestyles deemed the principal culprits.

“A healthy weight loss program, lifestyle enhancement, antioxidant agents, and nutrients targeting anti-inflammatory generally is a potentially effective strategy for treating PD.”

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

In regards to the study

The current study is registered with the International Prospective Register of Systematic Reviews (PROSPERO) database, and its methodologies were designed to comply with each 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 rating, UPDRS or MDS-UPDRS motor rating, 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 evaluate included publications for bias risk across all five of its beneficial parameters. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool was moreover used to judge data quality and effectiveness.

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

Study findings

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

Results of the current 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 dietary regimes, particularly the Mediterranean weight loss program, ketogenic diets, and other diets featuring low-protein intakes, significantly lowered UPDRS scores and mitigated motor PD symptoms.

“In the long run, it’s mandatory to conduct a studies sample size with sufficient power to judge how different sorts of dietary intervention affect individuals with PD.”