Over the last decade, researchers have found associations between ultraprocessed foods and health conditions like heart disease, Type 2 diabetes, dementia and some types of cancer.
Now, they are adding Parkinson’s disease to that list. In a study published Wednesday in the journal Neurology, researchers from the United States and China reported that people who consumed a lot of ultraprocessed foods were more likely to develop early signs of the disease than people who consumed less of them.
The finding is an association, not proof that ultraprocessed foods cause Parkinson’s disease, a progressive and incurable condition marked by tremors, muscle stiffness and other symptoms.
But studies like this one are critical for finding links between what we eat and neurological diseases, said Dr. Silke Appel Cresswell, a neurologist at the Pacific Parkinson’s Research Centre at the University of British Columbia who was not involved with the study.
It’s already established that what we eat plays a role in developing conditions such as heart disease, she said, but “we’re doing a bit of catch-up” when it comes to how it affects brain health. “This is where we need to start.”
What the New Study Found
Ultraprocessed foods and drinks are those made with ingredients you wouldn’t typically find in a home kitchen. The category, which includes soda, processed meats and many snack foods, accounts for more than half of the calories that adults in the United States consume.
For the study, the researchers investigated whether there was an association between eating these foods and developing early symptoms of Parkinson’s disease. Those included constipation, acting out dreams while sleeping, a reduced ability to smell, trouble telling the difference between colors, depression and daytime sleepiness.
The researchers analyzed diet questionnaire data from nearly 43,000 health professionals in the United States from the mid-1980s to the mid-2000s. Every two to four years, the participants, most of whom were white, were asked about the types and amounts of foods they typically consumed. Starting in 2012, they also self-reported their symptoms.
The researchers found that participants who ate the most ultraprocessed foods were about 2.5 times as likely to have at least three early symptoms of Parkinson’s disease compared with those who consumed the least.
If a person has these symptoms, it does not mean he or she will develop the disease, but it can signal brain changes that may lead to a diagnosis years later, said Dr. Alberto Ascherio, a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health and an author of the study.
In a previous study, Dr. Ascherio and his colleagues found that older men who had three early Parkinson’s symptoms — constipation, acting out their dreams and a reduced ability to smell — were 23 times as likely to be diagnosed with the disease three years later compared with men who did not.
Dr. Appel Cresswell said the study was strong because of its size, duration and use of detailed diet data collected over decades. It’s important to investigate early signs of Parkinson’s disease, she said, to help understand how lifestyle changes could slow or prevent the disease.
Still, the study had some limitations, Dr. Appel Cresswell said. She said she would have liked to see data on ultraprocessed food consumption and actual diagnoses of Parkinson’s disease. Dr. Ascherio said that he and his colleagues are currently investigating that.
Dr. Appel Cresswell also noted that the diet data, though detailed, was self-reported by participants, so it may not reflect exactly what and how much the participants ate. And other factors that were not included in the study, like participants’ sleep habits, could have affected their risk of Parkinson’s signs as well.
How Ultraprocessed Foods May Affect the Brain
How might eating ultraprocessed foods increase the risk of developing Parkinson’s disease? That’s “the billion-dollar question,” Dr. Ascherio said.
Perhaps certain additives in ultraprocessed foods or the chemicals in their packaging cause inflammation, cell damage or microbiome changes that eventually harm brain cells, he said.
It may also be that people who eat more ultraprocessed foods are missing out on healthier ones, like fruits, vegetables and legumes, which are rich in fiber, antioxidants and anti-inflammatory compounds, said Puja Agarwal, a nutritional epidemiologist at Rush University in Chicago who was not involved with the study. Research suggests that following a diet prioritizing these foods, such as a Mediterranean diet, is associated with a reduced risk of Parkinson’s disease.
What is needed now, Dr. Appel Cresswell said, are clinical trials with people who have early signs of Parkinson’s disease or have been diagnosed with it, to see if adopting a more healthful diet can prevent or delay the disease or slow its progression. But given what we already know, she said, there are only benefits to consuming fewer ultraprocessed foods and more whole foods — and not just for the brain.
Dr. Agarwal agreed. “If you are improving your diet, it’s not just for one thing,” she said. “What you eat for your brain is also good for your heart, is also good for your overall well-being.”
