What does the gut have to do with developing Parkinson’s disease?
Parkinson’s disease is an ever-worsening neurodegenerative disorder that results in death and affects about 1 in 50 people as they get older. A small minority of cases are genetic, running in families, but 85% to 90% of cases are sporadic, meaning they seem to pop up out of nowhere. Parkinson’s is caused by the death of a certain kind of nerve cell in the brain. Once about 70% of them are gone, the symptoms start. What kills off those cells? It still isn’t completely clear, but the abnormal clumping of a protein called alpha-synuclein or α-synuclein is thought to be involved. Why? Researchers injected blended Parkinson’s brains into the heads of rats and monkeys, and Parkinson’s pathology and symptoms were induced. It can even happen when injecting just the pure, clumped α-synuclein strands themselves. How, though, do these clumps naturally end up in the brain?
As I discuss in my video The Role Meat May Play in Triggering Parkinson’s Disease, it all seems to start in the gut. The part of the brain where the pathology often first appears is directly connected to the gut, and we have direct evidence of the spread of Parkinson’s pathology from the gastrointestinal (GI) tract to the brain: α-synuclein from brains of Parkinson’s patients is taken up in the gut wall and creeps up the vagal nerves from the gut into the brain—at least that was the case in rats. If only we could go back and look at people’s colons before they got Parkinson’s. Indeed, we can. Old colon biopsies from people who would later develop Parkinson’s were dredged up, and, years before symptoms arose, you could see the α-synuclein in their gut.
Research supported by the Michael J. Fox Foundation has found that you can reliably distinguish the colons of patients from controls by the presence of this Parkinson’s protein lodged in the gut wall. But how did it get there in the first place? Are “vertebrate food products…a potential source of prion-like α-synuclein”? Indeed, nearly all the animals with backbones that we consume—cows, chickens, pigs, and fish—express the protein α-synuclein. So, when we eat common meat products, when we eat skeletal muscle, we’re eating nerves, blood cells, and the muscle cells themselves. Every pound of meat contains, on average, half a teaspoon of blood, and that alone could be an α-synuclein source to potentially trigger a clumping cascade of our own α-synuclein in the gut. Though “it may seem intuitive that dietary α-synuclein could seed aggregation in the gut,” this kind of buildup, what evidence do we have that it’s actually happening?
We have some pretty interesting data. There’s a surgical procedure called a vagotomy, in which the big nerve that goes from our gut to our brain—the vagus nerve—is cut as an old-timey treatment for stomach ulcers. Would cutting communication between the gut and the brain reduce Parkinson’s risk? Apparently so, suggesting that the gut to brain’s vagal nerve may be critically involved in the development of Parkinson’s disease.
Of course, “many people regularly consume meat and dairy products, but only a small fraction of the general population will develop PD,” Parkinson’s disease. So, there must be other factors at play that “may provide an opportunity for unwanted dietary α-synuclein to enter the host, and initiate disease.” For example, our gut becomes leakier as we age, so might that play a role? What else makes our gut leaky? “Dietary fiber deprivation has also been shown to degrade the intestinal barrier and enhance pathogen entry.” So, this raises “possibilities for food-based therapies.”
Parkinson’s patients have significantly less Prevotella in their gut, a friendly fiber-eating flora that bolsters our intestinal barrier function. So, low levels of Prevotella are linked to a leaky gut, which has been linked to intestinal α-synuclein deposition, but fiber-rich foods may bring Prevotella levels back up. “Therefore, it is possible that by adopting a plant-based diet, in addition to the beneficial effects of phytonutrients, increasing overall fiber intake may modify gut microbiota and gut permeability [leakiness] in beneficial ways for people with PD.”
So, does a vegan diet—one with lots of fiber and no meat—reduce risk for Parkinson’s? Parkinson’s “appears to be rare in quasi-vegan cultures,” with rates that are about five times lower in rural sub-Saharan Africa, for instance. All this time, we were thinking the benefits seen for Parkinson’s from plant-based diets were due to the antioxidants and anti-inflammatory nature of the animal-free diets, but maybe it’s also due to the increased intestinal exposure to fiber and decreased intestinal exposure to ingested nerves, muscles, and blood.
Wasn’t that fascinating? For more on Parkinson’s, see the related posts below.
