Can diet alter the course of Parkinson’s Disease?
What is Parkinson's Disease (PD)?
Parkinson's Disease (PD) is the most common neurodegenerative disease with the exception of Alzheimer's. It is a chronic, progressive neurological disorder that involves degeneration of cells in the part of the brain that produce the neurotransmitter (chemical messenger in the brain) dopamine. Though symptoms vary from person to person, they often include loss of motor control as in slowness of movement, rigidity, tremor and balance problems as well as non-movement type symptoms such as constipation, low mood, fatigue, sleep and memory problems.
What causes PD?
Despite years of research the exact cause is unknown. However, it appears to involve a complex interaction of genetic and environmental factors. Contributory factors may include environmental toxicity, physical trauma, genetics, drugs, nutritional deficiency, mitochondrial (little power houses in our cells) dysfunction, enzyme deficiency, abnormal folding of a protein in the brain called α synuclein, and unremitting stress.
Current treatment
The mainstay of treatment for PD are drugs that replenish dopamine levels in the brain and simply provide symptomatic relief in early stages of the disease. Sadly, they don't address the underlying cause, and therefore don't slow or prevent progression of the disease. Disease modifying treatments that slow or halt the neurodegenerative process remain elusive and research is ongoing for compounds capable of tackling the multi dimensional features of PD.
So, what does nutrition have to do with Parkinson's?
Among environmental factors implicated in PD, nutrition is one of the most investigated areas as a potentially modifiable factor. There is a growing body of evidence to support the fact that diet can influence (positively or negatively) the development of neurodegenerative diseases such as PD. The Western diet, characterised by excessive intake of energy dense foods high in saturated and omega-6 fatty acids and refined sugars, excessive salt intake, and low consumption of omega-3 fatty acids and fibre is among the greatest risk factors for developing neurodegenerative diseases such as PD. Foods associated with more rapid PD progression include canned fruits and vegetables, fizzy drinks, fried foods, beef, ice cream and cheese (all characteristic of the Western diet). Food choice can improve PD symptoms, and some research suggests that sound nutritional choices could have disease modifying effects, such that they could potentially slow PD progression. Changing your eating habits can be a challenge, but there are many small adjustments that can be made to your diet that will add up to big benefits. Learning about them is the first step...
Plant based diet
A body of research suggests that what individuals eat and drink and the supplements they take may affect the risk of developing PD and its progression. Researchers have found that diets such as the Mediterranean diet (MedD), which is rich in fruit, vegetables, fish, legumes, nuts and seeds, olive oil, fresh herbs and spices, are associated with a lower risk of developing PD, reduced PD progression rate, as well as being helpful in the management of movement symptoms. This may in part be due to the fact that a variety of fruit and vegetables are rich in polyphenols (health promoting plant compounds), antioxidants, minerals, and vitamins that nourish and support the muscles, nervous system and organs of the body. Polyphenols in particular have been shown by numerous animal studies to be neuroprotective due to their antioxidant and anti inflammatory properties, but also because of their ability to inhibit the formation of α-synuclein (the protein that forms clumps in the brain, and is one of the main villains in PD).
One of the most dramatic differences between the traditional Western diet and the MedD is dietary fibre intake. Fibre intake is typically very low in Western societies, but high in those who consume a mediterranean diet. It follows that the mediterranean diet associated gut microbiota (resident gut bacteria) show an increase in the abundance of bacteria that feast on fibre to produce health promoting short chain fatty acids (SCFAs). These 'good' bacteria improve gut barrier function, insulin sensitivity and mitochondrial (energy power houses in our cells) function, and increase brain derived neutrotrophic factor (BDNF) production in the brain to name but a few benefits. BDNF essentially fertilizes the brain cells to keep them functioning and growing, as well as propelling the growth of new nerve cells.
When fibre intake is low however, our microbiota feast on protein instead, which favours the growth of 'bad' bacteria, and the production of metabolites that have been associated with insulin resistance (a feature of PD) and inflammation. In short, the various components of a Mediterranean diet (fibre, polyphenols, antioxidants and anti-inflammatory factors) can beneficially impact the brain, and therefore potentially reduce the impact of PD development and progression.
Omega 3 fatty acids
Consumption of omega 3 fatty acids (found in fish, seaweed, chia seeds and flax seeds), are also an element of the Mediterranean diet, and may have a role to play in the neurodegenerative process in PD, through their anti-inflammatory effects. Neuro-inflammation (inflammation of nervous tissue) plays a central role in PD. Dietary supplementation with omega 3 also reduces depression in those living with PD, and has been shown to reduce dopamine producing cell death in animal studies by increasing levels of BDNF in the brain. In addition to inhibiting nerve cell death, one type of omega 3 (DHA), promotes optimal dopamine producing cell structure and function through increasing the ability of the brain to change and adapt to new information, and improving communication between dopamine producing cells. DHA also protects the brain by increasing glutathione reductase (an enzyme involved in the production of glutathione, a potent antioxidant). The therapeutic potential of omega 3 fatty acids in impacting neuro-inflammation and the disease course of PD sufferers is very exciting, but needs further study.
Vitamin D
Vitamin D is a hot topic for research since it was discovered that we have receptors for it in the brain, and that like omega 3 fatty acids, it enhances BDNF. It also enhances antioxidant concentrations. Although research provides evidence supporting possible protective and symptomatic effects in PD, how vitamin D deficiency influences the risk for developing PD is unknown.
B vitamins
B vitamin deficiency is a frequent cause of neurological problems. The role of B vitamins in PD is linked to homocysteine which is a neurotoxin. People with PD have elevated levels of homocysteine caused by L-dopa (the most commonly used drug in the treatment of PD), which may accelerate dopamine producing cell death. High vitamin B intake reduces homocysteine levels and could therefore have a protective effect against PD.
Milk and dairy products
Increased consumption of dairy products has been reported in several studies to be associated with an increased risk of PD. The risk went up as dairy consumption increased. It is thought that this may be due to dairy products being contaminated with neurotoxins through their exposure to pesticides, but also due to the fact that milk and dairy products reduce blood uric acid levels, and uric acid is protective against PD.
Water
PD medications can raise the risk of dehydration, which if severe enough, can lead to confusion, weakness, balance problems, respiratory failure, kidney failure and even death. Adequate amounts of good quality filtered water is vital for people with PD, especially since they are likely to suffer from constipation. Tap water contains chlorine, which kills your good gut bacteria, so filtered water is recommended. Our brains are 80% water and our blood is 90% water. Critical processes like digestion, circulation and excretion cannot occur without it. It carries nutrients to all vital parts of the body, helps maintain body temperature, and serves as building material for the growth and repair of the body.
Eat organic
There is considerable evidence that dietary or environmental exposure to neurotoxin pesticides such as rotenone, paraquat, maneb and MPTP can promote Parkinson's -like neurodegeneration through damage to that part of the brain that is affected in PD, but also by modulating the gut microbiota. This strongly supports the recommendation to consume organic food wherever possible.
Diet and the PD microbiota
As well as impacting the body directly, diet may modulate the progression of PD indirectly through its effects on the gut microbiota (microbes that are resident in the gut). Diet is perhaps the single greatest factor determining their structure and metabolic function. The role of the gut microbiota and microbial metabolites have received increasing attention in regard to PD. It has been shown that both the number and make up of gut microbiota and microbial metabolites are altered in this disease. In particular, much lower levels of Prevotella species of bacteria (a type thought to be good for maintaining gut health) are found in people with PD. This decrease in abundance is associated with decreased levels of the gut hormone ghrelin, which participates in regulating dopamine producing neuron function in the part of the brain that is affected in PD. Prevotella may therefore have a role in fighting against neurodegeneration in PD. In fact, studies have shown that the abundance of Prevotella decreased with progression of PD!
In addition to low levels of Prevotella, higher levels of bacteria associated with gut inflammation have also been found in those with PD, which is in turn linked to neurodegeneration. Evidence is mounting of the proposed role of a pro inflammatory gut microbiome in PD. Chronic low grade inflammation could lead to leakiness of the blood-brain barrier, activation of immune cells and neuro-inflammation of the brain. The production of α-synuclein (the protein that forms clumps in the brain, and is one of the main villains in PD) might be initiated by a toxin or pathogen in the gut's nervous system which is transported to the brain via the vagus nerve.
Gut-microbiota-brain axis in PD
The gut-microbiota-brain axis is currently another hot research topic and describes the two way communication between the gut and the brain. This communication involves many mechanisms from bacterial components to bacterial metabolites to neurotransmitters (the body's chemical messengers), and hormones produced by gut cells. Gut bacteria, bacterial components and bacterial metabolites can trigger neurodegeneration in multiple ways which are affected by diet.The bi-directional communication that occurs is increasingly acknowledged as playing an important role in brain function including neurodegenerative diseases, and a better understanding of gut-brain interactions could provide new insights into the development of PD, and how to treat it. Case studies of the transplantation of faecal microbiota for example ('YUCK' I hear you say) have reported an improvement in symptoms in PD. If this proves to be the way forward for PD then I would be queuing up to receive a faecal transplant!!
How does all this relate to diet? What you eat affects which bacteria can thrive in your gut. If you want to stay healthy you need to keep your 'good' guests happy. Consumption of a typical Western diet promotes the growth of pro-inflammatory bacteria which disrupt the integrity of the gut barrier, ultimately leading to neuroinflammation and neurodegeneration. Conversely, consumption of a Mediterranean or whole food plant based diet, creates an environment where Prevotella and other healthy bacteria can flourish to produce short chain fatty acids (SCFAs) which fortify the gut barrier, normalise insulin resistance and stimulate the production of BDNF, all of which function to promote nerve cell health. The mediterranean diet is rich in fermentable fibre and other components of whole plant foods referred to as prebiotics because they feed the 'good' bacteria in our gut, and is highly likely to be beneficial for people with PD.
However, the causal link between abnormal gut microbiota composition and development of PD has yet to be established. The debate is whether these changes in the microbiota community structure and composition in PD is a trigger for PD, or a consequence of the disease. My guess is that the process is bi-directional, in that each influences the other. Current thought is that alterations in gut microbiota may be driving PD progression either via triggering inflammation of the gut and brain or by increased α-synuclein misfolding in the gut that results in clumps of α-synuclein being transported to the brain via the vagus nerve.
While the search goes on for mechanisms to explain PD abnormalities in gut microbiota, the most likely causes are Western lifestyle factors, including stress, Western diet, lack of exercise, and circadian disruption. It seems logical therefore that dietary interventions targeted at modifying the make up of our gut microbiota could alter the course of PD. As Hippocrates said: 'Let food be thy medicine and medicine be thy food'. It is in this spirit that diet has come to be recognised as both risk factor and therapy for PD
Probiotics and prebiotics
Probiotics are live microorganisms which provide health benefits by improving or restoring the balance of our gut microbiota. Probiotics and/or prebiotics may affect gut microbiota make up in regard to type, variety, and ratio, and may reduce inflammation of the gut and brain, reducing the likelihood of initiation and/or slowing down progression of PD. Studies have shown that supplementation of probiotics has reduced symptoms, and improved metabolic profiles, opening up new avenues in the management of PD. To reap maximum benefit from taking a probiotic however, it needs to be long term, as they don't hang around for long. Even if taken daily, adding probiotics alone is like sending a foot soldier to war without a box of ammunition. In order to thrive, these newly introduced microbes must be fed, and this is where a prebiotic and fibre rich whole food plant based diet come into play. Such optimisation of the gut microbiota in PD promises novel therapeutic approaches in regard to both symptomatic treatment and disease modification.