What Does Eating Plants Do For Parkinson’s Disease?

Parkinson’s disease is a progressive complex brain condition caused by deteriorating nerve cells.  Its symptoms include tremors and muscle rigidity, problems with thinking and memory, mood disorders, changes in speech and writing, pain, constipation, and sleeping difficulties.  More than 100,000 people in Canada are living with Parkinson’s right now.  (1)

Currently there is no cure for Parkinson’s disease but there is hope on the horizon.  Over the last couple of decades, numerous investigations have explored the effects on the brain of eating a plant-based diet rich in whole fruits and vegetables, high in plant proteins (nuts, seeds, beans and lentils) and whole grains and low in processed, refined sugar and meat, especially red meat.  Their results have revealed that eating mostly plants can play a major role in not only reducing the risk of and progression of Parkinson’s disease but also in maintaining good cognitive health.  (2,3,4,5)

Current studies have discovered that Parkinson’s disease begins in the gastrointestinal tract then spreads to the brain through the actions of the vagus nerve.  Parkinson’s patients have reported that they suffered from gastrointestinal symptoms such as constipation years before they were diagnosed with Parkinson’s.  (5,6)

In a study on mice from 2019 researchers found that the earliest signs of Parkinson’s occur in the enteric nervous system (also known as the “gut-brain axis”).  This is the strong connection that exists between the brain and the gut and involves the large vagus nerve which carries nerve signals in both directions.  Scientists discovered that abnormal misfolded alpha-synuclein (a protein found in the brain that regulates nerve cell signals and is linked to Parkinson’s disease) can spread from the gastrointestinal tract through the gut-brain axis into the brain.  Misfolded alpha-synuclein in the brain seems to cause normal alpha-synuclein to misfold in turn and these clumps of protein become the Lewy bodies which are hallmarks of Parkinson’s disease.  This is a clearcut link between the gut-brain axis and the development of and progression of Parkinson’s. (7)

It has been shown that Parkinson’s patients carry deposits of abnormal alpha-synuclein not only in their brains but throughout almost the entire length of their digestive tracts.  It appears that gut dysbiosis triggers inflammation-induced misfolding of proteins contributing to the development of Parkinson’s. Gut-to-brain spreading of pathological α-synuclein is currently being intensely studied in human Parkinson’s patients.  (7,8)

A 2023 study linked a healthy plant-based diet to significantly lower risks of Parkinson’s.  Using data from the huge UK Biobank cohort, the researchers found that participants who reported eating more healthy plant-based foods were 22% to 25% less likely to develop the disease. (15)

In December 2024 a study was published which compared the protective characteristics of various diets on nerves and how these factors might affect the development of Parkinson’s.  Diets involved in the study included Mediterranean, vegan, carnivore, paleo, and ketogenic diets.  In this work the plant-based Mediterranean diet and the healthy vegan diet were associated with the best outcomes including lower rates of Parkinson’s and slower progression of the disease. Researchers note that the benefits of the Mediterranean diet and the vegan diet appear to be coming from the rich content of antioxidant and anti-inflammatory compounds in both these diets. The other diets showed mixed results and the authors of this study called for future studies to focus on well-designed randomized controlled trials to clarify the  effects of various diets on Parkinson’s.  (9)

 

Mechanisms Behind The Favourable Effects of Eating Plants on Parkinson’s Disease 

Inflammation (10,11,12): 

Research from 1988 first suggested that inflammation could be contributing to the development of Parkinson’s disease.  Some studies had also found that the use of non-steroidal-anti-inflammatory drugs (NSAIDs) decreased the risk of developing Parkinson’s disease.   In addition, inflammation is known to be notably increased in patients with Parkinson’s disease.  Plant-based diets have been linked to reductions in markers of inflammation such as hs-CRP.  It is not yet clear whether inflammation is a cause of Parkinson’s disease or a result of the damaging effects of inflammatory processes.

Oxidative Stress (10,9): 

Oxidative stress is an imbalance of free radicals (molecules that are damaging to cells) and antioxidants (compounds that inactivate free radicals) which leads to the deterioration and death of neurons.  The brain consumes about 20% of the total oxygen supply of the body and a significant amount of that oxygen is converted to Reactive Oxygen Species (ROSs) as a natural by-product of the normal metabolism of oxygen. However, uncontrolled production of ROSs or inefficient elimination of ROSs by antioxidants will result in cell damage through oxidation.  This damage, known as oxidative stress, can occur in the neurons (brain cells) and in the mitochondria within neuron cells.  (Mitochondria are small organelles within cells that generate energy.)  Oxidative stress is now a well-accepted mechanism for the degeneration and death of neurons in Parkinson’s disease.

A diet rich in fruits and vegetables reduces oxidative stress through the rich supply of phytonutrients that plants contain. Phytonutrients, such as polyphenols and carotenoids, are naturally occurring protective chemicals for the plants that produce them which also have benefits for those eating the plants.  Phytonutrients reduce oxidative stress and lower cell death, support the healthy functioning of cells and boost the function of cell mitochondria.

Healthy plant-based diets are also high in antioxidants such as vitamin C and E which also help to reduce oxidative stress and inflammation, lowering the risk of cell damage linked to Parkinson’s.

  

The Gut-Brain Axis and the Gut Microbiome(7,8,5,6,10,16): 

Diet influences the gut-brain axis by altering the composition of microbes in the gut and by affecting the functions of neurons both within the vagus nerve pathway and in the central nervous system including the brain.  Most patients with Parkinson’s have a dysfunctional gut microbiome along with inflammatory changes in the intestinal lining, the vagus nerve and the brain.  Intestinal permeability (leaky gut) is increased in Parkinson’s.  The beneficial products derived from the metabolism of healthy microbes in the gut is lower in those with Parkinson’s compared to healthy subjects.

The vagus nerve, a long and substantial nerve that connects the gastrointestinal tract to the brain has been directly implicated in the spreading of Parkinson’s from the gut to the brain.  Studies on vagotomy surgery performed to control stomach acid production as a last resort treatment for intractable chronic peptic ulcer disease show that truncal vagotomy (surgery that cuts the main vagal nerve at the place where the esophagus meets the stomach) resulted in much lower rates of Parkinson’s than superselective vagotomy (surgery that cuts only the branch of the vagus nerve that triggers the output of stomach acid).  The risk of Parkinson’s in the group who had undergone a truncal vagotomy was decreased by 35% after the surgery while those who had had a superselective vagotomy showed no lowering of Parkinson’s risk.  The scientists followed up the truncal vagotomy group 20 years later and found that their rate of Parkinson’s had lowered even more and was only 50% of that of the superselective vagotomy group.

A whole-food plant-based diet encourages healthy gut microbes to flourish in the gut.  This is primarily due to the many types of fiber found in plants.  Note that there is no fiber present in animal-sourced foods.  Fiber promotes a diverse and stable population of healthy microbes and discourages unhealthy ones. Healthy microbes metabolize fiber by fermentation which results in short-chain fatty acids (SCFAs) such as acetate, propionate and butyrate that increase the health of the human host.  SCFAs are anti-inflammatory, improve immunity against pathogens, increase the integrity of the blood-brain barrier, support good brain function, supply raw materials for energy production and regulate critical functions of the intestine.  In Parkinson’s patients, the concentration of SCFAs in the intestine is significantly reduced. Researchers note that in parts of the world where plant-based diets are common, rates of Parkinson’s disease are lower.

 

Pollutants (10): 

Pollutants such as organochlorine compounds are very toxic compounds that do not easily break down in the environment and can accumulate in our bodies.

Humans are exposed to the organochlorine pollutant dieldrin through contaminated dairy products and meats.   Studies have shown that people exposed to pollutants such as dieldrin are at a 250% higher risk of developing Parkinson’s disease than are people who have not been exposed.  Those eating mostly plants have a much lower level of exposure to these pollutants.

 

Constipation (5): 

Constipation is present in approximately 80% of people with Parkinson’s disease.  A whole food plant-based diet is extremely rich in fiber which not only prevents constipation but also provides nutrients that are specifically required for our healthy microbes to thrive.  The result is both an increase in the healthy population of microbes and an increase in SCFAs, the by-products of these microbes, which have a vast array of healthy effects.

 

Fatigue and mood changes (5,13): 

A 2019 study examined multiple sources of research investigating the psychological benefits of eating plants.

Research from Australia encompassing over 12,000 adults followed for over 24 months found that increasing fruit and vegetable intake up to 8 portions daily was positively associated with happiness, life satisfaction and well-being.  The beneficial effect was equal in measure to the psychological impact of a transition from unemployment to employment.

Another population of over 60,000 middle-aged and older-aged adults assessed food intake and psychological distress over three years of follow-up and found that higher levels of fruit and vegetable intake was associated with lower prevalence of psychological distress.

In addition, curiosity, happiness and creativity appears to be increased in those eating fruits and vegetables.  A New Zealand study of 405 young adults found that those who ate more fruits and vegetables over a span of thirteen consecutive days reported “flourishing in their daily life with higher levels of well-being and intense feelings of curiosity and creativity” in contrast to a control group eating less fruits and vegetables who did not report changes in these psychological factors.

 

The Other Side of the Equation – The Effect of Eating Meat on Parkinson’s Disease (9,5)

• Eating red and processed meat is linked with many unhealthy outcomes such as increased incidence of metabolic syndrome, a condition that is correlated to higher risk of Parkinson’s disease.
• Meat-heavy diets result in excess protein intake which is associated with difficulty in the management of motor fluctuations and interference with the ability to move smoothly.
• The more meat consumed, the less fiber is eaten. Fiber is critical for a healthy gut microbiome.  In addition, low fiber contributes to constipation.
• Meat-heavy diets interfere with the absorption of some of the drugs used to alleviate the symptoms of Parkinson’s such as stiffness and tremors.

 

What Foods do the Health Professionals Looking After Parkinson’s Patients Recommend?

From the Parkinson’s Foundation in the USA comes the recommendation to eat mainly plant-based foods – fruits, vegetables, whole grains, seeds, nuts, olive oil – with the very occasional addition of dairy, seafood, chicken, turkey, or eggs if it can’t be avoided.  Stay away from red meats and sweets like cookies or candy.  (14)

Dr. John Duda, MD, national director of the Parkinson’s Disease Research, Education, and Clinical Center for the Department of Veteran Affairs and associate professor of neurology at the University of Pennsylvania’s Perelman School of Medicine, says, “The best evidence out there suggests that a whole-food, plant-based diet—a Mediterranean diet—is best for long-term health and wellness. The evidence is clear that adopting this type of diet will reduce your risk of dementia, depression, constipation, and a whole host of other things that will help you in the long run. A diet full of fiber and full of plant-based nutrients that include a whole host of antioxidants and anti-inflammatory molecules could help protect your brain. That’s the diet I recommend.”  (5)

 

SOURCES:

1  https://www.canada.ca/en/public-health/services/publications/diseases-conditions/parkinsonism.html

2 Maraki MI, Yannakoulia M, Stamelou M, et al. Mediterranean diet adherence is related to reduced probability of prodromal Parkinson’s disease. Mov Disord. 2019;34(1):48‐57. doi:10.1002/mds.27489

3 Mahlknecht P, Seppi K, Poewe W. The Concept of Prodromal Parkinson’s Disease. J Parkinsons Dis. 2015;5(4):681‐697. doi:10.3233/JPD-150685

4 Gao X, Chen H, Fung TT, et al. Prospective study of dietary pattern and risk of Parkinson disease. Am J Clin Nutr. 2007;86(5):1486‐1494. doi:10.1093/ajcn/86.5.1486

5  https://davisphinneyfoundation.org/plant-based-diet-for-parkinsons/

6  Svensson, E., Horváth-Puhó, E., Thomsen, R.W., Djurhuus, J.C., Pedersen, L., Borghammer, ,P., Sørensen, H.T. Vagotomy and subsequent risk of Parkinson’s disease. Ann Neurol. 2015 Oct;78(4):522-529. Doi: 10.1002/ana.24448. Epub 2015 Jul 17. PMID: 26031848.

7  Sorrentino, Z.A., Giasson, B.I. Exploring the Peripheral Initiation of Parkinson’s Disease in Animal Models. Neuron. 2019 Aug 21;103(4):547-549. Doi: 10.1016/j.neuron.2019.07.031. PMID: 31437447.

8  Skjærbæk, C., Knudsen, K., Horsager, J., Borghammer, P. Gastrointestinal Dysfunction in Parkinson’s Disease. J Clin Med. 2021 Jan 31;10(3):493. Doi: 10.3390/jcm10030493. PMID: 33572547; PMCID: PMC7866791.

9  Ansari, U., Omid, A, Nadora, Wen, J. Omid, A., Lui, F.   Review Outcomes of dietary interventions in the prevention and progression of Parkinson’s disease: A literature review. AIMS Neuroscience. December, 2024; 11 (4): 520–532. Doi:10.3934/Neuroscience.2024032

10  Strombom, A., Rose, S.  Preventing and Treating of Parkinson’s Disease with a Plant-Based Diet.  Open Access J Neurol Neurosurg 2021.  15(2).    Doi:10.19080/OAJNN.2021.15.555906.

11  McGeer,P.L., Itagaki, S., Boyes, B.E., McGeer, E.G. Reactive microglia are positive for HLA-DR in the substantia nigra of Parkinson’s and Alzheimer’s disease brains. Neurology (1988) 38:1285–91.

12  Menzel, J., Jabakhanji, A., Biemann, R., Mai, K., Abraham, K., Weikert, C. Systematic review and meta-analysis of the associations of vegan and vegetarian diets with inflammatory biomarkers. Sci Rep. 2020 Dec 10;10(1):21736. Doi: 10.1038/s41598-020-78426-8. PMID: 33303765; PMCID: PMC7730154.

13 Minich, D.M. A Review of the Science of Colorful, Plant-Based Food and Practical Strategies for “Eating the Rainbow”. J Nutr Metab. 2019 Jun 2;2019:2125070. Doi: 10.1155/2019/2125070. Erratum in: J Nutr Metab. 2020 Nov 28;2020:5631762. Doi: 10.1155/2020/5631762. PMID: 33414957; PMCID: PMC7770496.

14  https://parkinsonfoundation.org/blog/a-complete-parkinsons-diet-guide

15 Tresserra-Rimbau, A., Thompson, A.S., Bondonno, N., Jennings, A., Kühn, T., Cassidy, A. Plant-Based Dietary Patterns and Parkinson’s Disease: A Prospective Analysis of the UK Biobank. Mov Disord. 2023 Nov;38(11):1994-2004. Doi: 10.1002/mds.29580. Epub 2023 Aug 21. PMID: 37602951.

16 https://my.clevelandclinic.org/health/treatments/23390-vagotomy