A growing body of research suggests that the widespread consumption of ultra-processed foods (UPFs) may be contributing to mental health challenges, potentially through the ingestion of microplastics. A recent viewpoint published in the journal Brain Medicine explores this possible connection and calls for more rigorous investigation.
Ultra-Processed Foods Linked to Depression, Anxiety, Poor Sleep
Ultra-processed foods—industrial products made from ingredients derived from whole foods—have become a dietary staple in many high-income countries. In the United States alone, they account for over 50% of total caloric intake. Items such as instant noodles, packaged snacks, and sugary beverages are popular due to their affordability, convenience, and aggressive marketing.
However, numerous studies have raised concerns about their impact on mental health. An umbrella review cited in the viewpoint article found that high consumption of UPFs is associated with a 22% increased risk of depression, a 48% increase in anxiety, and a 41% rise in poor sleep outcomes. These findings echo results from randomized controlled trials, which show that diets rich in whole, unprocessed foods—such as the Mediterranean diet—can significantly alleviate depressive symptoms.
Microplastics: An Overlooked Contributor?
The authors of the Brain Medicine article argue that the link between UPFs and mental health issues may go beyond poor nutrition. They suggest that contaminants introduced during processing and packaging—including bisphenols and microplastics—may also play a role.
Microplastics and nanoplastics, often found in plastic packaging, are known to trigger oxidative stress, inflammation, immune dysfunction, and metabolic disturbances. In laboratory studies using animal models and cell cultures, these particles have been shown to damage brain cells and disrupt neurotransmitter function, raising concerns about their possible role in neuropsychiatric disorders.
While conclusive human data are lacking, the hypothesis remains concerning, especially in light of the omnipresence of plastic in food storage and preparation.
Diet as a Major Source of Microplastic Exposure
Ultra-processed foods are particularly prone to microplastic contamination, often due to storage and heating in plastic containers. For instance, studies have shown that chicken nuggets can contain up to 30 times more microplastics per gram than fresh chicken breast. Heating plastic containers in microwaves can release millions of micro- and nanoplastic particles within minutes.
In addition, bisphenol A (BPA), a chemical commonly used in plastic production, may leach into food products. Human studies have linked BPA exposure to increased risks of depression and autism.
“Cumulative exposure to microplastics and BPA through ultra-processed foods presents an emerging public health concern,” the authors warn.
Microplastics Detected in the Human Brain
Recent studies have confirmed the presence of microplastics in human brain tissue—predominantly polyethylene particles less than 200 nanometers in diameter. These concentrations were found to be 7 to 30 times higher than levels detected in organs such as the liver or kidneys. Between 2016 and 2024, the average microplastic load in brain samples increased by 50%, closely tracking the rise in UPF consumption.
While one study noted that individuals with dementia had three to five times more microplastics in their brains, researchers emphasize that the findings are correlative, not causal.
The Research Gap
Direct evidence linking microplastic exposure to mental health outcomes in humans is still scarce. This is largely due to the challenges of quantifying microplastic levels in human tissues and the ethical constraints surrounding controlled exposure studies.
The authors call for post-hoc analyses of existing dietary intervention trials to estimate potential reductions in microplastic intake and their corresponding mental health effects. One such study, the SMILES trial, showed that participants who switched from ultra-processed to nutrient-dense diets experienced significant improvements in depressive symptoms. Although the trial did not measure microplastic exposure, the findings support the theory that dietary changes could reduce the risk of mental health issues—possibly by limiting microplastic intake.
Proposing a Dietary Microplastic Index
To facilitate future research and public health assessments, the authors propose the development of a “Dietary Microplastic Index.” Similar to existing tools like the Dietary Inflammatory Index and the Nova classification system, this new index would estimate the microplastic burden of specific food items and overall dietary patterns.
Currently, no national nutritional surveys track microplastic intake, which limits the ability to analyze its long-term health impacts.
Looking Ahead
As ultra-processed food consumption continues to rise globally, so too does the urgency to understand its broader health implications. The accumulation of microplastics in the brain and body may be an overlooked but critical factor in the growing burden of mental health disorders.
“Given the emerging data, the need for comprehensive human studies investigating the relationship between dietary microplastic exposure and mental health is both timely and essential,” the authors conclude.
