Imagine a human brain sprinkled with colorful plastic confetti. That was the cover image of Brain Medicine in May 2025, announcing the most detailed look yet at a troubling idea: tiny plastic particles from the ultra‑processed foods many of us eat every day may be lodging in our brains—and possibly raising the risk of depression, dementia, and other mood disorders.

The special issue bundled four groundbreaking studies. Together, they paint a picture of a hidden pollutant hitchhiking from food wrappers and factory additives into our chicken nuggets, crisps, and soda bottles, then slipping through the blood‑brain barrier and settling inside the very organ that makes us us. On average, the researchers estimate, an adult brain now carries roughly “a spoonful” of microplastic dust. Among patients diagnosed with dementia, that burden was three to five times higher.

How did we get here, and what can we do about it? Let’s break down the science in simple language.

Microplastics 101

Microplastics are shards of plastic smaller than five millimetres—about the width of a pencil eraser. They are everywhere: drifting in sea spray, floating in drinking water, and now, apparently, hiding in our food. They form when larger plastic items—bags, bottles, synthetic clothing—crack and crumble with sunlight and wear. Industrial food processing, high‑speed chopping, and heat can also shear packaging into microscopic flakes that stick to oily or protein‑rich foods.

Because these fragments are so small, they can pass through the gut wall, enter the bloodstream, and circulate to distant organs. Until recently, scientists argued that the blood‑brain barrier—our brain’s microscopic security fence—was tight enough to keep them out. The new papers overturn that assumption.

Ultra‑processed foods: a plastic delivery system

Ultra-processed foods (UPFs)—like frozen pizzas, chicken nuggets, and packaged snacks—make up over half of daily calories in countries like the U.S. and U.K. According to Brain Medicine, UPFs contain significantly more microplastics than whole foods—chicken nuggets had 30 times more than chicken breast—due to plastic dust from processing equipment, packaging, and wrappers.

Why? Plastic dust from high‑speed blenders, conveyor belts, and even food‑grade gloves can mix into the final product; plastic‑lined wrappers and sachets may shed yet more debris.

Into the brain—and what happens next

Once microplastics breach the blood‑brain barrier, researchers believe they may trigger many of the same biological stress pathways already blamed for poor mental health in heavy UPF eaters:

• Inflammation – Plastic fragments can irritate brain‑resident immune cells, causing them to release inflammatory chemicals linked to low mood and neurodegeneration.
• Oxidative stress – Tiny plastics generate reactive oxygen molecules that damage neurons much like rust corrodes metal.
• Mitochondrial dysfunction – The “batteries” of nerve cells falter, sapping brain energy and resilience.
• Epigenetic change – Plastic additives such as phthalates may tweak gene switches that control mood and memory.
• Neurotransmitter disruption – Lab studies show plastic particles can alter levels of serotonin, dopamine, and GABA—the chemical messengers that balance emotion, reward, and relaxation.

Inflammation – Plastic fragments can irritate brain‑resident immune cells, causing them to release inflammatory chemicals linked to low mood and neurodegeneration.

Oxidative stress – Tiny plastics generate reactive oxygen molecules that damage neurons much like rust corrodes metal.

Mitochondrial dysfunction – The “batteries” of nerve cells falter, sapping brain energy and resilience.

Epigenetic change – Plastic additives such as phthalates may tweak gene switches that control mood and memory.

Neurotransmitter disruption – Lab studies show plastic particles can alter levels of serotonin, dopamine, and GABA—the chemical messengers that balance emotion, reward, and relaxation.

Put together, these mechanisms offer a plausible missing link: why diets packed with UPFs consistently predict higher rates of depression, anxiety, and even sleep troubles, over and above obesity or vitamin deficits.

Measuring what’s on your plate: the Dietary Microplastic Index

To move the field beyond horror headlines, the authors propose a Dietary Microplastic Index (DMI)—a simple scoring system that would estimate how much plastic a person ingests based on their weekly menu. Early pilot data suggest that swapping just two UPF servings a day for home‑cooked or “whole‑food” options could halve microplastic intake. Public‑health agencies are already exploring how food labels might one day display a DMI number, the way sodium and sugar are listed now.

Can we clean plastics out of the blood?

A tantalizing side note in the collection hints at a medical workaround. Extracorporeal therapeutic apheresis—a hospital procedure that filters a patient’s blood outside the body—has shown promise in removing circulating microplastics in preliminary trials. It’s the same technology used for certain autoimmune diseases and high cholesterol. While far from ready for routine mental‑health care, it suggests plastics are not permanently cemented in place and might be flushed out with the right tools.

What you can do today

Until regulators catch up and food companies redesign production lines, everyday eaters can take practical steps:

• Cook at home more often. Fresh produce, grains, and unprocessed meats contain far fewer microplastics.
• Choose whole over ground. A chicken thigh beats a nugget; whole‑bean coffee beats instant crystals.
• Mind your containers. Reheat leftovers in glass or ceramic, not in disposable plastic trays.
• Read labels skeptically. “Low‑fat” or “high‑protein” claims often mask ultra‑processing.
• Diversify your diet. Variety dilutes exposure to any single contaminant, plastics included.

Cook at home more often. Fresh produce, grains, and unprocessed meats contain far fewer microplastics.

Choose whole over ground. A chicken thigh beats a nugget; whole‑bean coffee beats instant crystals.

Mind your containers. Reheat leftovers in glass or ceramic, not in disposable plastic trays.

Read labels skeptically. “Low‑fat” or “high‑protein” claims often mask ultra‑processing.

Diversify your diet. Variety dilutes exposure to any single contaminant, plastics included.

These habits already line up with advice to curb heart disease and diabetes—protecting the brain becomes one more reason to adopt them.

The bigger picture

Microplastics reveal a troubling paradox: the convenience of ultra-processed foods may come at the cost of our brain health. While current research doesn't yet prove that microplastics cause mental illness, their presence in the brain and shared biological pathways with mood disorders raise serious concerns.

If tools like the Dietary Microplastic Index become widely used, the food industry may be pushed to reduce plastic contamination. Until then, choosing minimally processed foods isn’t just good for our bodies—it could be a vital step in protecting our minds.

Thanks for reading The Research Code’s Newsletter! This post is public so feel free to share it.

Share