Microplastics have officially crossed a new line: Our brains.

A growing body of research is raising serious concerns about the role of microplastics - tiny particles less than 5 millimeters in size - in brain health. One of the leading culprits? A familiar culprit - Ultra-processed foods (UPFs). 

In a study published in Nature Medicine earlier this year, scientists found that the average human brain may contain as many microplastics as a plastic spoon. The study also revealed a sharp 50% rise in brain microplastic levels between 2016 and 2024, with dementia patients showing even higher concentrations than those without cognitive decline. These plastic particles were more abundant in the brain than in the liver or kidneys.

Now, a series of four new papers published in Brain Medicine delves deeper into the connection between microplastics, ultra-processed foods, and declining mental health. The findings suggest that microplastics from UPFs might be contributing to rising global rates of dementia, depression, anxiety, and poor sleep.

“We’re seeing converging evidence that should concern us all,” said Dr. Nicholas Fabiano of the University of Ottawa, one of the paper’s co-authors. “Ultra-processed foods now make up more than half of energy intake in countries like the U.S., and these foods contain significantly higher levels of microplastics than whole foods.”

That claim is backed by data: highly processed items like chicken nuggets have been found to contain up to 30 times more microplastics per gram than whole foods like chicken breasts. The more processed the food, the more likely it’s been contaminated by packaging, production, and industrial handling. Microplastics don’t just pass through your system—they can cross the blood-brain barrier. Once inside the brain, they may trigger inflammation, oxidative stress, mitochondrial dysfunction, and other changes similar to those caused by poor diet and environmental toxins. These pathways have long been linked to neurodegenerative diseases like Alzheimer’s.

A 2024 review published in the British Medical Journal reinforces this link: people who consumed the most ultra-processed foods had a 22% higher risk of depression, 48% higher risk of anxiety, and a 41% higher risk of poor sleep. Researchers believe microplastics could be the missing link tying these health issues to food. “What emerges from this work is not a warning. It is a reckoning,” said Dr. Ma-Li Wong, professor of neuroscience at Upstate Medical University in New York. “The boundary between internal and external has failed. If microplastics cross the blood-brain barrier, what else do we think remains sacred?”

To tackle this emerging threat, scientists are calling for new tools—like a “Dietary Microplastic Index” to help people track their microplastic exposure through food. Some are also exploring radical solutions like apheresis, a method of filtering particles from the blood. But such treatments are still theoretical and require far more research.

In the meantime, the advice is clear: cut back on ultra-processed foods, push for safer packaging, and demand more research into how these invisible particles are affecting our brains. “As levels of ultra-processed food consumption, microplastic exposure, and mental health issues all rise together, we can’t afford to ignore the connections,” Fabiano said. “After all, you are what you eat.”