The Role of Pesticides in Parkinson’s Disease

In the original description of Parkinson’s disease by none other than Dr. James Parkinson himself, he described a characteristic feature of the disease: constipation, which may precede the diagnosis by many years. In fact, bowel movement frequency may be predictive. Men with less than one bowel movement a day were four times more like likely to develop Parkinson’s an average of 12 years later. This could be simply a really early symptom of the disease tied to decreased water intake, however. Many Parkinson’s patients report never really feeling very thirsty, and perhaps that led to the constipation. “Alternately, one may speculate that constipation also increases the risk of Parkinson’s disease as constipation results in a longer stay of the feces in the bowel and thus more absorption of neurotoxicants,” neurotoxins from the diet.

Two studies suggest an association between constipation and Parkinson’s, but, at the same time, 38 studies link the disease to pesticide exposure and by now more than 100 studies link pesticides to an increased risk of up to 80 percent.

Many of these studies are on occupational exposure, like that experienced by farmworkers, who may reduce their risk of Parkinson’s by wearing gloves and washing their clothes, but Parkinson’s has also been linked to ambient exposure. In the United States where approximately a billion pounds of pesticides are applied annually, just living or working in high-spray areas may increase Parkinson’s risk. It’s the same with using pesticides in the home. I didn’t realize how common household pesticide use was, and a study out of UCLA suggests it might not be such a good idea. 

Pesticides may cause DNA mutations that increase susceptibility for Parkinson’s or play a more direct role. Many neurodegenerative diseases appear to be caused by the buildup of misfolded proteins. In Alzheimer’s, it’s the protein amyloid beta; in Creutzfeldt-Jakob and mad cow disease, it’s prions; in Huntington’s, it’s a different protein; and in Parkinson’s disease, it’s a protein called alpha synuclein. A variety of pesticides—8 out of the 12 tested by researchers—were able to trigger synuclein accumulation in human nerve cells, at least in a petri dish, though the study has since been retracted so it’s unclear what the data actually showed.

The buildup of synuclein may play a role in killing off specialized nerve cells in the brain, 70 percent of which may be gone by the time the first symptoms arise. Pesticides are so good at killing these neurons that researchers use them to try to recreate Parkinson’s disease in animals. Is there any way to stop the process? As of this writing, there aren’t yet any drugs that can prevent this protein aggregation. What about flavonoid phytonutrients, natural compounds found in certain fruits and vegetables? Flavonoids can cross the blood-brain barrier and may have neuroprotective effects, so researchers tested 48 different plant compounds to see if any could stop the clumping of synuclein proteins into the little fibers that clog up the cell. And, indeed, they found a variety of flavonoids that can not only inhibit the spider web-like formation of synuclein fibers, but some could even break them up. It turns out flavonoids may actually bind to synuclein proteins and stabilize them.

In my video Berries vs. Pesticides in Parkinson’s Disease, you can see healthy nerve cells and the neurites, the arms they use to communicate to one another. After exposure to a pesticide, however, you can see how the cell is damaged and the arms are retracted. But, if you first incubate the nerve cells with a blueberry extract, the nerve cell appears better able to withstand the pesticide effects. So, this implies that flavonoids in our diet may be combating Parkinson’s disease as we speak, and healthy diets may be effective in preventing and even treating the disorder. However, these were all petri dish experiments in a laboratory. Is there any evidence that people eating berries are protected from Parkinson’s?

A study published quite a long time ago suggested the consumption of blueberries and strawberries was protective, but it was a tiny study and its results were not statistically significant. Nevertheless, that was the best we had…until now. In a more recent study, those eating a variety of phytonutrients were less likely to develop Parkinson’s disease. Specifically, higher intake of berries was associated with significantly lower risk. The accompanying editorial, “An Apple a Day to Prevent Parkinson Disease,” concluded that more research is necessary, but, until then, “an apple a day might be a good idea.” Of course, that’s coming from a man. Apples appeared protective against Parkinson’s for men, but not women. However, everyone appeared to benefit from the berries.

We may not want to have our berries with cream, though, as milk may be contaminated with the same kind of neurotoxic pesticide residues found in the brains of Parkinson’s disease victims.


I’ve produced other videos on Parkinson’s disease, including: 

Learn about other neurological muscular disorders, including essential tremor and ALS:

The same reason Parkinson’s may be related to constipation may also explain the breast cancer connection. For more on this, see my video Breast Cancer and Constipation.

What else can berries do?

But what about all the sugar in fruit? See my videos If Fructose Is Bad, What About Fruit? and How Much Fruit Is Too Much?.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

What to Feed Your Gut Bacteria

For many years, it was believed that the main function of the large intestine was just to absorb water and dispose of waste, but “[n]owadays it is clear that the complex microbial ecosystem in our intestines should be considered as a separate organ within the body,” and that organ runs on a MAC, microbiota-accessible carbohydrates. In other words, primarily fiber.

One reason we can get an increase of nearly two grams of stool for every one gram of fiber is that the fiber fermentation process in our colon promotes bacterial growth. The bulk of our stool by weight is pure bacteria, trillions and trillions of bacteria, and that was on a wimpy, fiber-deficient British diet. People who take fiber supplements know that a few spoonfuls of fiber can lead to a massive bowel movement, because fiber is what our good gut bacteria thrive on. When we eat a whole plant food like fruit, we’re telling our gut flora to be fruitful and multiply.

From fiber, our gut flora produce short-chain fatty acids, which are an important energy-source for the cells lining our colon. So, we feed our flora with fiber and then they turn around and feed us right back. These short-chain fatty acids also function to suppress inflammation and cancer, which is why we think eating fiber may be so good for us. When we don’t eat enough whole plant foods, though, we are in effect starving our microbial selves, as I discuss in my video Gut Dysbiosis: Starving Our Microbial Self. On traditional plant-based diets, we get lots of fiber and lots of short-chain fatty acids, and enjoy lots of protection from Western diseases like colon cancer. In contrast, on a standard American diet filled with highly processed food, there’s nothing left over for our gut flora. It’s all absorbed in our small intestine before it even makes it down to the colon. Not only may this mean loss of beneficial microbial metabolites, but also a loss in the beneficial microbes themselves.

Research shows the biggest issue presented by a Western diet is that not leaving anything for our bacteria to eat results in dysbiosis, an imbalance wherein bad bacteria can take over and increase our susceptibility to inflammatory diseases or colon cancer, or maybe even lead to metabolic syndrome, type 2 diabetes, or cardiovascular disease.

It’s like when astronauts return from space flights having lost most of their good bacteria because they’ve had no access to real food. Too many of us are leading an “astronaut-type lifestyle,” not eating fresh fruits and vegetables. For example, the astronauts lost nearly 100 percent of their lactobacillus plantarum, which is one of the good guys, but studies reveal most Americans don’t have any to begin with, though those who eat more plant-based are doing better.

So it’s use it or lose it. If people are fed resistant starch, a type of MAC found in beans, within days the bacteria that eat resistant starch shoot up and then die back off when you stop. Eating just a half can of chickpeas every day may “modulate the intestinal microbial composition to promote intestinal health” by increasing potentially good bacteria and decreasing pathogenic and putrefactive bacteria. Unfortunately, most Americans don’t eat beans every day or enough whole grains, enough fruits, or enough vegetables. So, the gut flora—the gut microbiota—of a seemingly healthy person may not be equivalent to a healthy gut flora. It’s possible that the Western microbiota is actually dysbiotic in the first place just because we’re eating such fiber-deficient diets compared to populations that may eat five times more fiber and end up with about 50 times less colon cancer.


This is one of the reasons I recommend three daily servings of legumes (beans, split peas, chickpeas, and lentils) in my Daily Dozen checklist.

The microbiome connection may explain the extraordinary results in the study I featured in my video Is It Worth Switching from White Rice to Brown?.

More on the musical fruit:

More on the microbiome revolution in medicine:

For more on bowel health, check out:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Stop Creating So Many Free Radicals in Your Colon

Colon cancer risk in Westernized populations may be reduced by decreasing animal product intake and thereby decreasing  “aggressive” factors as animal protein and fat. I’ve explored how animal protein can putrefy and produce the rotten egg gas that may be toxic to DNA (see Putrefying Protein and “Toxifying” Enzymes), but what about the fat? It can stimulate the synthesis and secretion of bile acids into the intestine.

Bile helps the body digest fats. So, more fat in the intestines means more bile in the intestines, which wouldn’t be a problem except bile acids, especially secondary bile acids, have long been suspected as being carcinogenic. Bile acids stimulate the growth of bacteria, which convert the primary bile acids our livers make into secondary bile acids. And, secondary bile acids have been shown to be cancer-causing.

As described in my How to Reduce Carcinogenic Bile Acid Production video, this could help explain why fat-rich diets are correlated with colon cancer. High saturated fat intake is associated with elevated levels of bile, which is what you tend to see in people with colon cancer. As such, they are considered tumor-producing factors in colorectal cancer development and perhaps also breast cancer, as these secondary bile acids can get absorbed into the blood stream and circulate throughout the body. (See Breast Cancer and Constipation for more on this.)

This may help explain the extraordinarily low rates of colon cancer in sub-Saharan Africa, with native Africans putting out just a fraction of the secondary bile acids of African Americans. Well, if a diet high in animal fat stimulates the growth of these toxic and carcinogenic secondary bile salt-producing bacteria, what about diets that don’t include any animal fat? We’ve known for more than 40 years that those eating plant-based diets have less bile in their stools and a reduced capacity to create colon carcinogens. Those eating vegetarian produce just a fraction of some of the secondary bile acids implicated in cancer—about 70% less. Within just one week on a plant-based diet, the bacterial enzyme activity to produce these secondary bile acids is cut in half. Within a month, their presence is cut in half, as well.

One of the most important toxic effects of these bile acids—the BAs in our BMs—is the increased production of free radicals. That’s one of the ways they can damage our DNA and undermine our DNA repair pathways.

Hydroxyl radicals are one of the most destructive free radicals, which may increase colon cancer risk. They only last about a billionth of a second but, in that time, can convert harmless substances in the bowel to DNA-damaging, mutagenic substances, and bile acids are believed to promote this process. But, if you switch people to a vegetarian diet for only 12 days, you can get a 13-fold drop in hydroxyl free radical production.

So, fecal free radicals may activate carcinogens in the colon. On a standard American diet, the amount of free radicals produced in the stool is quite remarkable, corresponding to that which would be produced by a fatal dose of gamma radiation. So, what do we do about it? What’s an achievable, practical measure to decrease free radical formation in our colon? We could attempt to “colonize the colons of high risk patients with genetically engineered, antioxidant-producing bacteria,” but why not just eat a more plant-based diet?

What about fiber? See Fiber vs. Breast Cancer for more information on why fiber may be so protective.

You can find more on the microbiome in Stool pH and Colon Cancer, Preventing Ulcerative Colitis with Diet, and Why Do Plant-Based Diets Help Rheumatoid Arthritis?.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: