Exploring the relationship between gut health and neurodegenerative disease
MDlinx Oct 11, 2023
Research has been buzzing about medical insights believed to be buried in the gut. The gut and the brain communicate through a complex network known as the gut-brain axis. This intricate system involves the bidirectional flow of information between the central nervous system and the enteric nervous system, which is embedded in the gut lining.
Emerging studies have demonstrated that disturbances in the gut microbiome can lead to dysregulation in this axis, potentially contributing to the development of neurodegenerative diseases like Parkinson’s and Alzheimer’s disease.
As our understanding of this dynamic relationship continues to evolve, prioritizing gut health may offer a head start advantage in the fight against these debilitating and difficult-to-treat conditions.
Understanding the brain-gut connection
Diseases like Parkinson’s disease are now understood as more than just neurological. A review on inflammation and the immune system in Parkinson’s disease states that patients with Parkinson’s show high inflammation in multiple body systems, leading to nonmotor symptoms including immune dysfunction, sleep disturbances, and gastrointestinal issues.
Tansey MG, Wallings RL, Houser MC, et al. Inflammation and immune dysfunction in Parkinson disease. Nat Rev Immunol. 2022;22(11):657–673.
Before the onset of motor symptoms, Lewy bodies begin to develop in the gut’s enteric nervous system, as noted in an article in Neurology.
Chen SJ, Chen CC, Liao HY, et al. Association of fecal and plasma levels of short-chain fatty acids with gut microbiota and clinical severity in patients with Parkinson disease. Neurology. 2022;98(8):e848–e858.
Additionally, a strong overlap has emerged between Parkinson’s disease and inflammatory bowel disease (IBD), according to the review authors. In one meta-analysis, IBD patients had almost 30% greater risk for Parkinson’s.
Treating IBD patients with anti-TNF biologics appeared protective, lowering the odds of Parkinson’s by 78%. Italian researchers reported that colon and stool biopsies of people with Parkinson’s have identified elevated inflammatory markers, and mucosal biopsies show a lower number of tight-junction–related proteins.
Bisaglia M. Mediterranean diet and Parkinson’s disease. International Journal of Molecular Sciences. 2023;24(1):42.
In their conclusion, the researchers stated that, “due to the activation of the intestinal inflammatory response and the gut leakage, the peripheral activated immune cells can migrate into the brain, promoting the breakage of the blood-brain barrier and connecting in such a way the systemic inflammation to the brain.”
Protective effects of short-chain fatty acids
Despite the complex observations on specific bacterial strains and immune pathways, much of the data on gut health boils down to the benefits of dietary fiber.
The Italian researchers postulate that short-chain fatty acids (SCFAs) strengthen the mucosal lining and play a central role in reducing gut permeability and inflammation.
Fiber fermentation in the gut leads to the production of SCFAs. Studies cited by the Neurology authors show that several types of SCFA are lower in persons with advanced Parkinson’s vs those in the earlier stages of the disease. In addition, low concentrations of SCFA are also found in Alzheimer’s disease, suggesting a potential target for proactive therapies.
Qian XH, Xie RY, Liu XL, et al. Mechanisms of short-chain fatty acids derived from gut microbiota in Alzheimer's disease. Aging Dis. 2022;13(4):1252–1266.
Dietary changes to promote a healthy gut
High-fiber diets, including Mediterranean and vegetarian diets, are consistently associated with protection against neurodegenerative diseases. Conversely, the Western diet, which is notoriously low in fiber and high in sugar and red meat, increases disease risk and progression.
While more research is warranted, patients need strategies they can use immediately. The Academy of Nutrition and Dietetics says that encouraging patients to meet their minimum daily requirements of 25 grams of fiber for women and 30 grams for men through antioxidant-rich plant foods is a practical step in the right direction.
Larson H. Easy ways to boost fiber in your daily diet. Academy of Nutrition and Dietetics. February 2021.
The brain benefits of fiber also extend to its ability to regulate blood sugar, an emerging risk factor for Alzheimer’s disease and dementia.
Zhang YR, Xu W, Zhang W, et al. Modifiable risk factors for incident dementia and cognitive impairment: An umbrella review of evidence. J Affect Disord. 2022;314:160–167.
While the evidence for other food types isn’t as well defined, several sources suggest that incorporating foods like yogurt, kefir, kimchi, sauerkraut, and kombucha may help restore and maintain a healthy microbiome. In addition, excessive consumption of sugar and processed foods can disrupt the balance of gut microbiota, favoring the growth of pathogenic bacteria.
Clinicians can offer education on which foods are highest in fiber and can refer patients to a dietitian if they are struggling to get enough.
Eating the skin on fruits and vegetables, replacing processed foods with more whole foods, and incorporating beans and lentils in the diet can help patients reach their fiber needs.
To reduce digestive discomfort, patients should be encouraged to increase fiber gradually and drink plenty of water.
What this means for you
Most people should be eating more fiber for gut health and disease prevention, particularly fermentable soluble fiber. In addition, providers may want to pay special attention to the heightened risk of neurodegenerative disease with bowel disease, weighing the benefits of more aggressive therapies to reduce inflammation before it’s too late to protect the brain.
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