A study is among the first to examine how microplastics found in certain foods and even tap water interact with the human gut
Microplastics found in the human gut have been linked to the development of depression.
Early research is among the first to examine how different types of microplastics commonly found in the environment interact with the human gut microbiome. The gut microbiome, or the complete collection of microorganisms in the human gut, is increasingly being referred to by scientists as the “second brain” as we learn more about its vast impact on our health and mood.
It contains trillions of micro-organisms including good and bad bacteria which interact with our immense systems and affect how our bodies function and develop. The new study used stool samples from five healthy volunteers to grow gut microbiome cultures in the lab.
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These cultures were then exposed to five common microplastic types.
Some of these microplastics induced changes in the microorganisms in the gut that were similar to those previously seen in people with depression and colorectal cancer.
Lead author Christian Pacher-Deutsch, of research institution CBmed and the Medical University of Graz, cautioned that this was not proof that microplastics could cause depression, but added: “These findings are significant given how pervasive microplastic exposure is in everyday life.
“Microplastics have been found in fish, salt, bottled water, and even tap water, meaning that most people are exposed daily through ingestion, inhalation and skin contact. The key takeaway is that microplastics do have an impact on our microbiome.
“While it’s too early to make definitive health claims, the microbiome plays a central role in many aspects of well-being, from digestion to mental health. Reducing microplastic exposure where possible is therefore a wise and important precaution.”
Microplastics are miniscule plastic particles smaller than 5mm and we are increasingly aware how they now permeate human environments.
The five common microplastic types which microbiome cultures were exposed to were polystyrene, polypropylene, low-density polyethylene, poly(methyl methacrylate) and polyethylene terephthalate.
Christian Pacher-Deutsch said: “At this stage, the exact pathways remain unclear, but several plausible explanations are emerging. Microplastics may change microbial composition by creating physical or chemical environments that favour certain bacteria. For instance, biofilms can form on microplastic surfaces, providing new niches that some microbes colonise more rapidly.”
Further analysis revealed certain bacterial groups increasing or decreasing depending on the microplastic type. Changes were observed across several bacterial families, including Lachnospiraceae, Oscillospiraceae, Enterobacteriaceae and Ruminococcaceae. The majority occurred within the phylum Bacillota which is a key group of gut bacteria important for digestion and overall gut health.
These shifts in bacterial composition were accompanied by changes in the chemicals produced by the bacteria and a significant increase in acidity levels.
The findings are being presented at the New research presented today at United European Gastroenterology Week 2025 event in Berlin. The United European Gastroenterology is a professional non-profit organisation combining all leading European medical societies focussing on digestive health.
Christian Pacher-Deutsch added: “Microplastics may also carry chemical substances that directly influence bacterial metabolism. This can lead to changes in acid production, which may serve as a bacterial stress response, unintentionally altering the gut’s pH.
“These shifts could then trigger feedback loops that further affect the balance of the microbiome.”