People who eat more ultra-processed foods show more early signs of Parkinson’s, study finds

A new study has found that people who consume high amounts of ultra-processed foods are more likely to exhibit early symptoms associated with Parkinson’s disease than those who consume less. The findings, published in Neurology, suggest that dietary habits may be linked to nonmotor symptoms that often occur years before Parkinson’s disease is diagnosed. However, the researchers emphasized that their study does not prove cause and effect.

Parkinson’s disease is a neurodegenerative disorder that progresses slowly, often beginning with subtle, nonmotor symptoms such as sleep disturbances, constipation, and mood changes before movement-related symptoms appear. This early phase, known as the prodromal phase, can last for over a decade. Since early interventions could potentially slow or delay the onset of Parkinson’s disease, researchers have been increasingly interested in identifying risk factors that arise long before diagnosis. Diet is one such candidate.

Previous research has shown that high consumption of ultra-processed foods is associated with an increased risk of dementia, prompting scientists to explore whether similar patterns exist for Parkinson’s disease.

“We previously showed that people with poor diet quality had a high future risk of Parkinson’s disease, suggesting the important role of diet in the development of the condition. Recently, ultra-processed food, which are strongly associated with poor diet quality, have been shown to be associated with dementia, another major neurodegenerative disease. However the relation between ultra-processed food and Parkinson’s disease remained unknown,” said study author Xiang Gao of the Institute of Nutrition at Fudan University.

To investigate this, the researchers analyzed data from two large, long-running studies: the Nurses’ Health Study and the Health Professionals Follow-Up Study. These studies have tracked health and lifestyle factors in tens of thousands of U.S. adults over several decades. For the current research, the team focused on a sample of 42,853 participants (about 59% women, with an average age of 48 years). They excluded individuals who had already been diagnosed with Parkinson’s disease, were over the age of 85, or had missing or implausible dietary data.

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Dietary habits were assessed using food frequency questionnaires collected every two to four years. Participants reported how often they ate various foods, which were then categorized using the NOVA classification system. This system groups foods into categories based on how much processing they undergo, with ultra-processed foods including items like sugary cereals, packaged snacks, sweetened beverages, and processed meats. The researchers calculated average long-term intake of ultra-processed foods and examined how it related to a set of seven early indicators of Parkinson’s disease.

These early symptoms, or prodromal features, included probable REM sleep behavior disorder (where people physically act out their dreams), constipation, reduced sense of smell, color vision impairment, daytime sleepiness, unexplained body pain, and depressive symptoms. Each symptom counted as one point, and the researchers compared participants with no symptoms to those with one, two, or three or more.

The results showed a clear pattern: people who consumed the most ultra-processed foods were significantly more likely to show multiple prodromal symptoms. Compared to those who ate the least, individuals in the highest fifth of ultra-processed food consumption were about 2.5 times more likely to exhibit three or more early signs of Parkinson’s disease. This association remained even after adjusting for factors like age, physical activity, smoking, caffeine, alcohol intake, overall diet quality, and total calorie intake.

When the researchers looked at individual symptoms, they found that high ultra-processed food consumption was linked to greater odds of having sleep behavior disorder, constipation, body pain, and depressive symptoms. However, there was less consistent evidence for an association with reduced sense of smell, color vision issues, or daytime sleepiness.

To better understand whether these associations could be driven by specific types of foods, the team also analyzed subcategories of ultra-processed foods. They found that packaged sweet snacks, processed meats, artificially sweetened drinks, dairy-based desserts, and sauces or condiments were particularly associated with the presence of prodromal symptoms.

Importantly, the study was designed to reduce the possibility that people already experiencing early symptoms had changed their diets in response. To do this, the researchers looked only at dietary data collected at least six years before the earliest assessment of prodromal symptoms. They also conducted additional analyses using dietary information from as far back as 1986 and found similar associations.

“Healthy dietary patterns, high in fruits and vegetables and low in ultra-processed foods, could be beneficial against risk of Parkinson’s disease, an incurable neurodegenerative disease,” Gao told PsyPost.

But the researchers cautioned that their findings cannot prove that ultra-processed foods directly contribute to the development of Parkinson’s disease. Because this was an observational study, it’s possible that other unmeasured factors—such as environmental exposures or genetic risk—could explain the association.

There are also limitations in how diet and symptoms were measured. Diet was self-reported, which can introduce errors or biases. The categorization of foods as “ultra-processed” can be imprecise, especially for items that contain both processed and unprocessed ingredients. In addition, not all participants completed assessments for every prodromal feature, and the sample was mostly composed of White health professionals, which may limit how widely the results apply.

Nevertheless, the authors suggest that their findings are consistent with other research linking poor diet quality to neurological decline. They also highlight several possible biological mechanisms that could explain the relationship between ultra-processed foods and brain health. These foods often contain additives, artificial sweeteners, and packaging-related chemicals that have been shown in laboratory studies to increase inflammation, oxidative stress, and damage to dopamine-producing neurons—the same type of brain cells that are lost in Parkinson’s disease.

Another potential explanation involves the gut. Ultra-processed foods are typically low in dietary fiber and can disrupt the gut microbiome, which plays a role in inflammation and may be involved in Parkinson’s-related processes. Some researchers believe that Parkinson’s disease might begin in the gut and travel to the brain via the vagus nerve, a hypothesis supported by emerging evidence.

While more research is needed, especially interventional studies that test whether reducing ultra-processed food intake can prevent or delay Parkinson’s disease, the current findings provide one more reason to be mindful of diet. In particular, focusing on whole foods—such as fruits, vegetables, legumes, and unprocessed grains—might not only benefit general health but also reduce the risk of neurological decline later in life.

The study, “Long-Term Consumption of Ultraprocessed Foods and Prodromal Features of Parkinson Disease,” was authored by Peilu Wang, Xiao Chen, Muzi Na, Mario H. Flores-Torres, Kjetil Bjornevik, Xuehong Zhang, Xiqun Chen, Neha Khandpur, Sinara Laurini Rossato, Fang Fang Zhang, Alberto Ascherio, and Xiang Gao