As scientists uncover growing levels of microplastics in the brain, new evidence suggests your favorite convenience foods could be quietly affecting your mental health—sparking urgent calls for research and dietary change.
Study: Microplastics and mental health: The role of ultra-processed foods. Image Credit: SIVStockStudio / Shutterstock
A new viewpoint article published in the journal Brain Medicine highlights a possible role of microplastics in influencing the association between ultra-processed food intake and mental health adversities.
Ultra-processed foods and mental health
Ultra-processed foods, such as instant noodles, carbonated drinks, and packaged foods, are industrial formulations made from substances derived from whole foods. These food products contain high amounts of industrial additives and involve sophisticated packaging.
The consumption of ultra-processed foods is rapidly increasing worldwide, especially in high-income countries. In the United States, these foods are associated with more than 50% of energy intake. Convenience, affordability, accessibility, aggressive marketing, and lifestyle changes are the major factors driving the global dietary shift from whole foods to ultra-processed foods.
According to an umbrella review published in The BMJ and referenced in the viewpoint, people who consume ultra-processed foods have a 22% higher risk of depression, a 48% higher risk of anxiety, and a 41% higher risk of poor sleep outcomes compared to those with lower intake.
Recent observational studies indicate that excessive consumption of ultra-processed food is associated with poor sleep quality, physical health adversities, depression, and anxiety. This evidence is further supported by studies reporting that higher consumption of nutrient-rich, unprocessed foods potentially reduces the risk of mental disorders. Small randomized controlled trials, particularly those examining Mediterranean diet interventions in people with depression, have demonstrated moderate-to-large improvements in depressive symptoms. The findings of recent interventional studies also clearly indicate a link between dietary intake and mental health.
Microplastics as a contributing factor
Mental health adversities associated with ultra-processed food intake might be attributed to their poor nutrient profiles, energy density, and physical or chemical properties related to industrial processing and packaging methods, which introduce bisphenols and microplastics as contaminants.
Similar to ultra-processed foods, microplastics are known to induce oxidative stress, inflammation, immune dysfunction, altered metabolism, impaired cell growth and organ development, and carcinogenicity.
Microplastics and nanoplastics can increase the risk of neuropsychiatric disorders by inducing oxidative stress in the brain, causing nerve cell damage, and influencing the functionality of neurotransmitters, such as acetylcholine, γ-aminobutyric acid, and glutamate. However, it is important to note that much of the mechanistic evidence on microplastics and neurological effects comes from animal and cell culture studies, with limited direct human data.
Sources of microplastics in diet
Because of processing and packaging methods, ultra-processed foods contain high amounts of microplastics. These foods are often stored and heated in plastic containers, a significant source of microplastics. For example, chicken nuggets can contain 30 times more microplastics per gram than chicken breast, and microwaving some plastic containers may release millions of microplastic and nanoplastic particles within minutes. Besides microplastics, bisphenol A used in plastic production can be released and mixed with ultra-processed foods when plastics degrade. Bisphenol A has been specifically associated with autism and depression in some human studies. These observations clearly indicate that excessive consumption of ultra-processed foods can accumulate microplastics and bisphenol A in the body.
Microplastics in the human brain
Emerging evidence highlights the presence of microplastics in the human brain. These microplastics, mainly polyethylene, are smaller in diameter (less than 200 nanometers) and are 7 to 30 times higher than those found in other organs, such as the liver or kidney. A recent study also found a 50% increase in brain microplastic concentration from 2016 to 2024, paralleling the ongoing rise of ultra-processed foods. One recent study found that people with dementia had three to five times higher levels of brain microplastics, but the authors emphasize this correlation does not imply causation.
Although some human studies have shown a link between bisphenol A exposure and risk of autism, depression, and anxiety, no evidence is currently available linking microplastic exposure to mental health adversities. This gap in knowledge is partly due to the difficulty in quantifying microplastic exposures in the human brain from an observational perspective and the ethical limitations surrounding microplastic exposure in interventional studies.
Implications for dietary intervention
Identifying microplastics in the brain and throughout the body raises significant health concerns. Several studies have highlighted the potential negative impact of microplastics on immune functions, genetic stability, and endocrine functions.
The SMILES trial is the first randomized controlled trial to investigate the efficacy of adjunctive dietary intervention in treating moderate to severe depression. The main aim of the dietary intervention was to replace nutrient-deficient, ultra-processed foods with nutrient-rich, unprocessed foods. The trial findings indicated significant improvement in depression among participants who consumed the intervention diet for 12 weeks. Compared to the 8% control group participants, remission was achieved for 32% of intervention group participants. This means that for approximately every four people who adopted the dietary changes, one additional person experienced remission from depression, compared to the control group (a measure known as the “number needed to treat,” which was 4.1).
Although the trial did not directly measure microplastic accumulation in participants’ bodies, it is imperative to hypothesize that the improvement in depression is associated with a reduction in microplastic exposure due to dietary substitutions. However, this remains a hypothesis requiring further investigation, as microplastic exposure was not directly measured.
The viewpoint notes that it would be valuable to conduct post-hoc analyses in such dietary trials, retrospectively estimating changes in microplastic content due to dietary interventions and their potential effect on mental health outcomes, as more data on microplastic content in foods becomes available.
Need for a new dietary risk index
While the paper notes that research quantifying the microplastic content of various ultra-processed food items is becoming increasingly available, it does not state that methods are already well-established for all foods. It would be of prime importance to evaluate the changes in microplastic content due to dietary interventions and their subsequent effect on various mental health outcomes.
Several diet-based risk indices have been developed to assess the long-term impact of dietary exposure on physical and mental health. The Dietary Inflammatory Index has been developed to assess the inflammatory potential of a person’s diet based on the foods they consume. Similarly, the Nova food classification system has been developed to categorize foods based on the extent and purpose of industrial processing.
Given the significant utility of these indices, the authors of this article propose designing a Dietary Microplastic Index to assess the microplastic content and risk of accumulation based on the foods consumed.
Currently, no nutritional population-based surveys estimate or track microplastic intake via diet, which precludes robust analysis of long-term microplastic exposure and adverse mental health outcomes.
The global rise in the intake of microplastic-enriched ultra-processed foods, together with the simultaneous induction in mental health adversities, highlights the need for more research to investigate this association in humans.