Patients and families have long known about the connection between Parkinson’s disease and the GI tract. That’s because gastrointestinal dysfunction is one of the most common non-motor symptoms of Parkinson’s disease, and like so many of these symptoms, it often goes untreated. However, as research in the field has advanced, there is a growing awareness of the importance of gastrointestinal function in the etiology of Parkinson’s disease. Many researchers now recognize the role of the brain-gut-microbiota axis in the onset and development of the condition. Not only may changes in the microbiome be responsible for gastrointestinal dysfunction in Parkinson’s disease patients, but they may also be linked to some of the characteristic neurological symptoms of the condition, including tremors, visual problems, and dementia. This has led to calls for the development of a microbiome diet for Parkinson’s disease that may help ameliorate symptoms and slow the progress of the condition.
The Connection Between Parkinson’s Disease and the Microbiome
In recent years, there have been multiple studies suggesting that that the microbiome in patients with Parkinson’s disease is compositionally different from that of healthy patients. For instance, in 2018, a group of researchers from the University of Luxembourg reported statistically significant differences in the type and abundance of bacterial species in the GI tracts of patients with Parkinson’s disease, as compared to healthy controls. Notably, this association was also true for patients with idiopathic rapid eye movement sleep behavior disorder, a prodromal condition that is seen as a red flag for the future development of Parkinson’s disease. This suggests that the composition of the microbiome plays a role in both the onset of the disease and its progress over time.
When considering the possibility of a microbiome diet for Parkinson’s disease, it is important to look at which types of bacteria are different in the GI tracts of patients with the condition, as well as the functional impacts of these changes. A particularly insightful study addressing these topics was conducted by a group of researchers at Rush University Medical Center in Chicago in 2015. These researchers collected fecal samples from 38 Parkinson’s disease patients and 34 healthy controls, and they found that the abundance of butyrate-producing bacteria from the genera Blautia, Coprococcus, and Roseburia was far lower in patients with Parkinson’s disease than their healthy counterparts. Moreover, the patients with Parkinson’s disease were found to have higher levels of bacteria known to promote inflammation, including bacteria from the genus Ralstonia. These distinctions were associated with higher levels of colonic inflammation in the Parkinson’s disease patients. This suggests that anti-inflammatory dietary strategies, possibly including butyrate supplementation, may be a pillar of a future microbiome diet for Parkinson’s disease patients.
Another study out of Saarland University in Germany supports this notion. Like the researchers who conducted the first study, they compared the gut microbial composition of 34 Parkinson’s disease patients with 34 healthy controls. Once again, they found that the abundance of bacteria that produce short-chain fatty acids like butyrate was far lower in the gut microbiota of patients with Parkinson’s disease. They also extended the study to include measurements of the actual levels of short-chain fatty acids produced by the bacteria remaining in the gut in order to evaluate whether the lack of these bacteria was actually having an impact on short-chain fatty acid levels. Indeed, the lack of bacteria ultimately meant lower concentrations of short-chain fatty acids in the GI tracts of patients with Parkinson’s disease. This deficiency may be playing a role in the dysfunction of the gut-brain axis and the exacerbation of debilitating symptoms.
Preliminary Dietary Intervention Attempts for Patients with Parkinson’s Disease
Given the potential connections between gastrointestinal dysfunction and the motor and non-motor symptoms of Parkinson’s disease, a microbiome diet for Parkinson’s disease may prove to be an effective treatment option. However, scientific studies on this possibility are still in their infancy. One of the interventions that have been proposed involves increasing the intake of probiotics, either through supplementation or through the consumption of fermented foods, since this strategy directly introduces beneficial bacteria in the gut microbiome. In 2011, researchers at the Parkinson Institute in Milan, Italy, explored this idea by testing the efficacy of milk fermented with the probiotic strain Lactobacillus casei Shirota for treating patients with Parkinson’s who were also suffering from constipation. There was a statistically significant decrease in constipation symptoms among the 40 Parkinson’s disease patients who took part in the study, but the researchers did not extend the study to include an evaluation of how the dietary therapy might have impacted the patients’ neurological symptoms via the gut-brain axis. Therefore, additional research is warranted in the future.
Another relevant study from 2012 examined the potential neuroprotective benefits of curcumin, the active compound in turmeric, a spice that is commonly used in Indian food. As a polyphenol, it makes sense that curcumin might ameliorate some of the symptoms associated with dysfunction of the gut-brain axis, given its well-established role as an anti-inflammatory compound. As previously mentioned, colonic and neuronal inflammation have both been observed in Parkinson’s disease, and multiple studies suggest that curcumin intake (either in the diet or in bioavailable supplements) may have potential as a dietary therapy.
In 2017, a group of researchers from Bastyr University Research Institute in Washington adopted a much more broad approach to early research on the development of a microbiome diet for Parkinson’s disease patients. Instead of evaluating the impacts of a specific type of food, the researchers conducted a survey of over a thousand individuals with Parkinson’s disease to determine which foods were associated with slower progression of the condition and which were associated with faster progression. They found that the foods that were significantly associated with slower progression of the disease included fresh vegetables, fresh fruit, nuts, seeds, non-fried fish, olive oil, coconut oil, wine, fresh herbs, and spices. There were also two nutritional supplements associated with a decrease in progression rate: coenzyme Q10 and fish oil. At the same time, the researchers found statistically significant associations between faster Parkinson’s disease progression and canned fruit, canned vegetables, soda (diet and nondiet), fried foods, beef, ice cream, yogurt, cheese, and iron supplementation. While it is not clear how clinically relevant all of these associations may be, the findings may provide a basic foundation for a microbiome diet for Parkinson’s disease in the future.
The Bottom Line: Making Dietary Changes for Parkinson’s Disease
Given the relative lack of clinical studies on specific dietary interventions, there is not yet a single microbiome diet for Parkinson’s disease that can be recommended for all patients. However, it is clear that anti-inflammatory foods and supplements like butyrate and curcumin may play a role in the disease etiology, so it could be worth considering how they might help resolve symptoms through their anti-inflammatory activities and their support for the gut-brain axis. Nutrient-dense fruits and vegetables, as well as probiotic foods, also seem like they may have positive effects, as they do for so many health conditions. However, the field is still wide open for researchers, and it will be exciting to see where the data leads in the future. As the research progresses, patients and practitioners will be able to gain a better understanding of the connections between nutrition and Parkinson’s disease, which can ultimately lead to the development of a more specific microbiome diet for Parkinson’s disease patients.
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