Webinar: Diet and the gut vs the brain

The gut-brain axis refers to the network of neurons connecting the gut to the brain. This axis allows the two entities to interact and influence each other, such as when we get a stomach ache when we are anxious.

Historically, we have viewed Parkinson’s through a ‘brain-first’ lens, meaning dopamine neuron dysfunction and neurodegeneration is initiated within the brain. However, given the prevalence of gastrointestinal (GI) issues in people with Parkinson’s, especially during the prodromal (pre-diagnosis) period, researchers now propose that in some people Parkinson’s may have another origin: the gut. This hypothesis is referred to as the ‘gut-first’ or ‘body-first’ model of Parkinson’s.

One proposed mechanism for this is the transport of dysfunctional alpha-synuclein via the gut-brain axis, initiating alpha-synuclein pathology¹ in the brain. The build-up of dysfunctional copies of the protein alpha-synuclein is a hallmark of Parkinson’s progression and considered a major driver of dopamine neuron death. This hypothetical pathway is still in its early stages, however, evidence such as the presence of alpha-synuclein aggregates in the gut tissues of prodromal Parkinson’s patients² supports further investigation.

One of our panelists, Prof Per Borghammer, has spent much time researching and developing this hypothesis. If you are interested in learning more about these models, we recommend his 2019 paper,

Brain-First versus Gut-First Parkinson’s Disease: A Hypothesis (2019), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6839496/.

Citations

¹ Neuropathological evidence of body-first vs. brain-first Lewy body disease (2021),

² Pathological α-synuclein in gastrointestinal tissues from prodromal Parkinson disease patients (2016),

The gut microbiome is the collection of microorganisms – including bacteria, fungi, and viruses – that naturally live in our digestive track. The gut microbiome can be a great ally, helping us digest food, protecting us against infection, and producing vitamins we cannot obtain otherwise. However, when imbalanced, it could lead to health problems and may contribute to the development of certain diseases. There is still a lot we don’t know about the gut microbiome and how it is regulated; however, we do know it is very susceptible to change and can be impacted by a range of factors, such as age, nutrition, lifestyle, hormones, or antibiotics.

In recent years, a spotlight has been turned to the gut microbiome and whether it may play a role in Parkinson’s development. Considering we know the gut microbiome communicates with the brain via the gut-brain axis, and that gut issues, especially constipation, are common symptoms of Parkinson’s, it is no wonder that researchers are interested in uncovering this potential relationship.

Recently, researchers have been investigating whether there are any major differences in the gut microbiomes of people with Parkinson’s. summarizes most of what we know so far.

Parkinson’s disease and gut microbiota: from clinical to mechanistic and therapeutic studies (2023),

Most gut bacteria resides in the colon, also known as the large intestine, whereas the small intestine is relatively bacteria-free. Small intestinal bacterial overgrowth, or SIBO, occurs when there is too much bacteria in the small intestine, often causing bloating, pain, diarrhoea, constipation and/or unexpected weight loss.

There is some evidence to suggest that people with Parkinson’s are more likely to develop SIBO. One study found that up to 50% of people with Parkinson’s tested positive for SIBO (compared to only 5-10% in people without Parkinson’s)¹; however, there is still a lot we do not know about the condition or what can predispose you to it.

Citations

¹ Association of small intestinal bacterial overgrowth with Parkinson’s disease: a systematic review and meta-analysis (2021),

Gut issues are not only one of the most common non-motor symptoms of Parkinson’s, but also are some of the first symptoms people experience, often years before the onset of motor symptoms and/or diagnosis. Constipation, for example, is suggested to occur in 50-80% of Parkinson’s patients, with an estimated 25% of patients experiencing constipation during the prodromal (pre-diagnosis) stage¹. Gastroparesis is also common², which is defined by the weakening of the muscles in the stomach, leading to the slower digestion of food.

Several gut-related conditions are also associated with being risk factors for Parkinson’s, and, in the context of the gut-brain axis, may even be a facilitator of disease onset. Leaky gut syndrome, for example, is suggested to play a role³. This condition occurs when the lining of the intestines is damaged, allowing easier passage of molecules from the gut into the bloodstream. This damage is usually the result of prolonged gut inflammation, such as that experienced in inflammatory bowel diseases (IBDs). IBDs are also considered a risk factor for Parkinson’s⁴.

Citations

¹ Parkinson disease with constipation: clinical features and relevant factors (2018),

² Gastroparesis in Parkinson Disease: Pathophysiology, and Clinical Management (2021),

³ The gut-brain axis: is intestinal inflammation a silent driver of Parkinson’s disease pathogenesis? (2017)

⁴ Inflammatory Bowel Diseases and Parkinson’s Disease (2019),

Probiotics are live bacteria and yeasts suggested to have various health benefits. There have been some encouraging studies suggesting that probiotics can help with constipation in Parkinson’s¹; but to date, no probiotic has been approved by regulators for use in Parkinson’s. Increasing the diversity of bacteria in the gut can sometimes have positive benefits, but one should consult with your doctor/neurologist before changing any aspect of your treatment regime as it may affect how medication is absorbed by the body.

Citations

¹ Probiotics for Constipation in Parkinson Disease: A Randomized Placebo-Controlled Study (2021)

Overall, research into diet management in Parkinson’s is extremely limited, and currently there is still much we do not know. There has been some evidence suggesting people with Parkinson’s should be mindful of their protein intake as high-protein diets may impact the effectiveness of their medications, such as levodopa¹. A high-sugar intake may also be associated with worsening symptoms; however, this relationship is still not well understood².

Ultimately, diet is very individualized and there is no one diet that will work for every person with Parkinson’s. People with Parkinson’s should consult with a dietician if they are interested in making changes their diet.

Citations

¹ To restrict or not to restrict? Practical considerations for optimizing dietary protein interactions on levodopa absorption in Parkinson’s disease (2023)

²  Increased Added Sugar Consumption Is Common in Parkinson’s Disease (2021),