 Parkinson's disease is an ever-worsening neurodegenerative disorder that results in death and affects about 1 in 50 of us when we get older. A small minority of cases are genetic and run in families, but 85 to 90% of cases are sporadic, meaning they just seemingly pop up out of nowhere. It's caused by the death of a certain kind of nerve cell in the brain. Once about 70% of them are gone, the symptoms start. OK, so what kills off those cells? It's still not completely clear, but the abnormal clumping of a protein called alpha-synuclein is thought to be involved. Why? Because if you inject blended Parkinson's brains into the heads of rats or monkeys, you can induce Parkinson's pathology and symptoms, or even just injecting the pure clumped alpha-synuclein strands themselves. OK, but how do these clumps naturally end up in the brain? It all seems to start in the gut. The part of the brain where the pathology often first shows up is directly connected to the gut, and we have direct evidence of the spread of Parkinson's pathology from the gastrointestinal tract to the brain. Alpha-synuclein from brains of Parkinson's patients taken up in the gut wall and creeping up the vagal nerves from the gut into the brain, but this was in rats. If only we had a way to go back and look at people's colons before they got Parkinson's. And indeed, we can. Old colon biopsies were dredged up from people who would later develop Parkinson's, and years before symptoms arose, you could see the alpha-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 the Parkinson's protein lodged in the gut wall. But how did it get there in the first place? Perhaps vertebrate food products as a potential source of prion-like alpha-synuclein. See, nearly all the animals with backbones that we eat, cows, chickens, pigs, and fish, express the protein, alpha-synuclein. And 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 has like a teaspoon to a tablespoon of blood in it, and that alone could be an alpha-synuclein source to potentially trigger a clumping cascade of our own alpha-synuclein in the gut. Though it may seem intuitive that dietary alpha-synuclein could seed this kind of buildup in our gut, what evidence do we have that it's actually happening? These are pretty interesting data. There's a surgical procedure called vagotomy, which the big nerve that goes from your gut to your brain 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 vagal nerve may be critically involved in the development of Parkinson's disease. Now, of course, many people regularly consume meat and dairy products, but only a small fraction of the general population will develop Parkinson's. So there must be other factors at play that may somehow provide an opportunity for unwanted dietary alpha-synuclein to enter the host and initiate disease. For example, your gut becomes leakier as you age, so might that play a role? Well, what else makes your gut leaky? Dietary fiber deprivation has also been shown to degrade the intestinal barrier and enhance pathogen entry. So this all raises possibilities for food-based therapies. Parkinson's patients have significantly less prevetella in their gut, a friendly fiber-eating floor that bolsters your intestinal barrier function. So low levels of prevetella is linked to a leaky gut, which has been linked to intestinal alpha-synuclein deposition. But fiber-rich foods may bring prevetella levels back up. Therefore, by adopting a plant-based diet, in addition to getting the beneficial effects of phytonutrients, it's possible that increasing overall fiber intake may modify the gut microbiome and gut leakiness in beneficial ways. So does a vegan diet, one with lots of fiber, no meat, reduce risk for Parkinson's disease? Parkinson's does appear to be rare in quasi-vegan cultures, rates are about five times lower in rural Sub-Saharan Africa, for instance. And now all this time we were thinking the benefits seen for Parkinson's from plant-based diets was 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.