What does the intestine have to do with the onset of Parkinson’s disease?
Parkinson’s disease is a progressively worsening and fatal neurodegenerative disease that affects approximately 1 in 50 people as they age. A small number of cases are hereditary and run in families, but 85% to 90% of cases are sporadic and seem to come out of nowhere. Parkinson’s disease is caused by the death of certain types of nerve cells in the brain. Once about 70% of them are gone, symptoms begin. What causes those cells to die? Although not completely understood, it is thought to involve abnormal aggregation of a protein called alpha-synuclein or α-synuclein. why? Researchers injected mixed Parkinson’s disease brains into the heads of rats and monkeys to induce Parkinson’s disease pathology and symptoms. It can also occur when pure aggregated α-synuclein chains are injected themselves. But how do these clumps naturally reach the brain?
It all seems to start in the gut, as I explain in my video “The Role of Meat in Inducing Parkinson’s Disease.” The part of the brain where the disease often first appears is directly connected to the gut, and there is direct evidence that Parkinson’s disease pathology spreads from the gastrointestinal (GI) tract to the brain. Alpha-synuclein from the brains of people with Parkinson’s disease is taken up by the intestinal wall and travels up the vagus nerve from the intestines into the brain. At least in rats. I wish I could go back and look at people’s colons before they had Parkinson’s disease. Sure, it’s possible. Dredging of old colon biopsies from people who later developed Parkinson’s disease showed alpha-synuclein in their intestines years before symptoms appeared.
A study supported by the Michael J. Fox Foundation found that the presence of this Parkinson’s disease protein, which lodges in the intestinal wall, can reliably distinguish the colons of patients from those of controls. But how did we get there in the first place? Are vertebrate foods a potential source of prion-like alpha-synuclein? In fact, nearly all animals with skeletons that we consume, such as cows, chickens, pigs, and fish, express the protein alpha-synuclein. So when we eat common meat products, when we eat skeletal muscle, we are eating nerves, blood cells, and the muscle cells themselves. On average, every pound of meat contains half a teaspoon of blood, which alone is a source of alpha-synuclein and can trigger our own alpha-synuclein aggregation cascade in the gut. “It may seem intuitive that dietary alpha-synuclein could cause aggregation in the gut,” but what evidence is there that this kind of accumulation actually occurs?
There’s some pretty interesting data. The traditional treatment for stomach ulcers is a surgical procedure called vagotomy, which involves cutting the vagus nerve, a thick nerve that connects the intestines to the brain. Would cutting off communication between the gut and the brain reduce the risk of Parkinson’s disease? Apparently so, suggesting that the vagus nerve from the gut to the brain may be crucially involved in the development of Parkinson’s disease.
Of course, “many people consume meat and dairy products regularly, but only a small proportion of the general population develops PD, or Parkinson’s disease.” Therefore, there must be other factors at play that “could provide an opportunity for unwanted alpha-synuclein from food to enter the host and cause disease.” For example, our intestines become leaky as we age, but could that play a role? What else makes our intestines leaky? “A lack of dietary fiber has also been shown to lower the intestinal barrier and facilitate pathogen invasion.” So this offers “dietary potential.”
The intestines of Parkinson’s disease patients have significantly fewer Prevotella bacteria, a friendly flora that feeds on dietary fiber that strengthens the intestinal barrier function. Therefore, low levels of Prevotella lead to leaky gut, which is associated with α-synuclein deposition in the intestines, while fiber-rich foods may restore Prevotella levels. “Thus, in addition to the beneficial effects of phytonutrients, adopting a plant-based diet may increase overall fiber intake and alter gut microbiota and intestinal permeability (leaky) in ways that are beneficial for PD patients.”
So, does a vegan diet high in fiber and meat-free reduce the risk of Parkinson’s disease? Parkinson’s disease “appears to be rare in quasi-vegan cultures,” with prevalence rates around one-fifth lower in rural areas of sub-Saharan Africa, for example. We have long thought that the benefits seen in Parkinson’s disease from a plant-based diet were due to the antioxidant and anti-inflammatory properties of the animal-free diet, but it may also be due to increased exposure to fiber in the gut and decreased exposure in the gut to ingested nerves, muscles, and blood.
Wasn’t that fascinating? For more information about Parkinson’s disease, see the related articles below.
