Study links UPFs to early signs of Parkinson’s disease, experts urge caution

A newly published study in Neurology has investigated the potential link between ultra-processed foods (UPFs) and early signs of Parkinson’s disease, sparking reactions from leading researchers in the field who praised the study’s scale but advised caution in interpreting its findings. 

Professor Jules Griffin, director of the Rowett Institute at the University of Aberdeen, UK, highlights the study’s significance in exploring how diet could be tied to impact brain health. “We’ve known for some time that unhealthy diets can contribute to vascular dementia and Alzheimer disease.”

He adds that this study adds to growing evidence that diet plays a role in neurodegenerative conditions like Parkinson’s. “Just like we give out advice for healthy eating for type 2 diabetes and cardiovascular disease, we should be doing the same for a healthy and functioning mind.”

Diet and cognitive decline

The longitudinal analysis included participants without a history of Parkinson’s disease. UPF consumption was assessed using repeated food frequency questionnaires (between 1984 and 2006) and grouped based on Nova classification. 

Participants provided data on probable REM sleep behavior disorder (pRBD) and constipation in 2012. Between 2014 and 2015, a subset of participants provided data on five additional nonmotor features, including hyposmia, impaired color vision, excessive daytime sleepiness, body pain, and depressive symptoms.

However, Griffin highlights several caveats of the study, pointing out that changes in gut function and sleep may not be specific to Parkinson’s. “They are not directly looking at Parkinson’s disease but some of the symptoms that are associated with the very early stages of the disease,” he notes.

He also raises questions about whether UPFs themselves are to blame, or whether they act as a marker for generally poor diets high in saturated fat, sugar, and salt — already linked to cognitive decline.

Dr. Katherine Fletcher, research lead at Parkinson’s UK, echoes concerns about the limitations of dietary research, flagging challenges such as recall bias and subjective interpretation. “People often will inaccurately self-report what their diet comprises,” she notes.

Fletcher also points out the lack of ethnic and socio-economic diversity in the study group, which primarily included US-based health professionals.

Study strengths and limitations

Despite these limitations, Fletcher acknowledges the study’s strengths, including its long-term follow-up and relatively large sample size. “This paper builds on previous research, such as the work of Dr. Laurie Mischley [Bastyr University, US]... which has shown an association between processed foods and faster progression of Parkinson’s,” she notes.

Scientists reference the protective benefits of a Mediterranean-style diet in preventing Parkinson’s disease.Fletcher also references existing evidence suggesting that a Mediterranean-style diet could reduce the risk of developing the disease.

Eef Hogervorst, professor of Psychology at Loughborough University (UK), was more critical of the study’s conclusions. “The outcome term ‘early symptoms of Parkinson’s disease’ is a bit misleading,” she says.

Hogervorst says symptoms such as constipation and body pain are common in older adults and not necessarily predictive of Parkinson’s. She also has concerns about the classification of UPFs in the study, citing inconsistencies and questioning how certain processed foods were categorized.

“It seemed strange that non-UPF food included beef, pork, lamb chicken or turkey sandwich (all processed meats)... as well as distilled alcohol and dairy coffee,” notes Hogervorst.

She emphasizes that not all UPFs were associated with early Parkinsonian symptoms, and that foods linked to diabetes and vascular disease — such as sweets and savory snacks — may influence brain health via different pathways. “These symptoms are not necessarily predictive of Parkinson’s disease, nor were these symptoms individually all associated with UPF consumption,” she concludes.

Cautioning careful interpretation

Dr. Daniel J van Wamelen of King’s College London finds the study to be “based on solid research” but urges careful interpretation. “The findings in this study are interesting and appear to be based on solid research,” he notes.

However, he clarifies that the symptoms assessed were not definitive indicators of Parkinson’s disease. “While the study found that people who ate more ultra-processed foods tended to report more of these non-motor symptoms, it did not find a direct increase in the risk of Parkinson’s disease itself.”

Van Wamelen stresses the need for longer-term data. “To better understand the long-term implications, we would need a longer follow-up to see how many participants go on to develop Parkinson’s and how this is associated with their diet.”

“The connection to Parkinson’s disease should be viewed with caution until more definitive evidence becomes available,” he concludes.