A new study by Imptox researchers reveals how everyday microplastics can hitch a ride into our digestive system, interact with gastrointestinal enzymes and food proteins, and subtly interfere with how our body breaks down food.

Picture this: a perfectly grilled steak on your plate. You cut into it, savor the flavor, and your stomach gets to work with its usual cast of digestive characters - among them, trypsin, a key enzyme that breaks down proteins into absorbable fragments. But what if this meaty scene had an invisible intruder?

Tiny fragments of plastic - microscopic in size, practically weightless - may have made their way into your meal. They aren’t doing anything obvious. They don’t make you sick right away. But they’re not just passing through, either.

In a world where plastic pollution is everywhere - from ocean trenches to human bloodstreams - a team of researchers from the University of Belgrade and the University of Vienna, both partners in the EU-funded Imptox project, asked a new kind of question: What happens when microplastics collide with our digestive enzymes? Their findings, published in the International Journal of Molecular Sciences, reveal a surprisingly intimate interaction between plastic particles and trypsin, and hint at broader implications for how microplastics may be reshaping the microscopic world inside us.

Microplastics: More Than Just Passengers

It is well known that humans and animals are increasingly ingesting microplastics - particles smaller than 5 mm - through a wide variety of foods, beverages, and even dust. But what happens after ingestion? Are these tiny synthetic particles merely passive stowaways? Or are they playing an active role in the complex chemistry of digestion?

To explore this, the researchers studied two common plastic types: polypropylene (PP) and polyethylene terephthalate (PET) - materials often used in food packaging and drink bottles. They looked at how these microplastics interact with the digestive enzyme trypsin, as well as proteins from beef meat extract, including α-Gal-carrying allergens - molecules that can trigger severe allergic reactions in certain individuals.

How Proteins and Plastics Stick Together

Once inside the digestive system, microplastics interact with gastrointestinal enzymes and food proteins, forming what scientists call a ‘corona’ on the microplastics’ surface. This corona can take two forms: soft coronas, where proteins are loosely attached and exchange frequently, and hard coronas, where proteins are more firmly bound.

Trypsin was among the proteins that attached to the surface of PP and PET microplastics. When bound, trypsin underwent subtle structural changes. Although these changes did not disable the enzyme, they slightly reduced its activity - especially in the hard corona, where trypsin activity dropped significantly. Meat proteins and α-Gal allergens were also drawn into the corona layer, temporarily coating the plastic particles.

Subtle Effects with Bigger Questions

According to the authors, it is unlikely that realistic concentrations of microplastics in the intestine would have significant effects on meat extract proteins’ and allergens’ digestibility by trypsin. Even at the relatively high concentration tested in the study, the observed effects were subtle: digestion of most proteins continued as normal. Additionally, the breakdown of α-Gal allergens, which can trigger immune responses in some individuals, was not significantly affected. However, digestion is only one part of the picture.

Microplastics, through the formation of protein coronas, might influence not just digestion but also how the immune system perceives food components. When allergens like α-Gal bind to microplastics, they could be presented to the immune system in altered forms. This could have consequences for allergen absorption, transport, and recognition, factors that may contribute to growing trends in food allergies and inflammatory gut conditions.

Microplastics, in other words, are not passive. They can bind, modify, and disable biological molecules. Their presence in our digestive system may subtly disrupt the gut’s delicate chemical balance - a finding that raises new questions about long-term health risks.

A Microscopic Puzzle with Public Health Implications

This study is just one part of the broader research effort underway in the Imptox project, which seeks to understand how micro- and nanoplastics, especially in combination with environmental pollutants, influence the risk of allergic diseases. Nanoplastics - even smaller than the particles studied here - are particularly concerning, as they can cross biological barriers easily and reach deep tissues and organs, adding a new layer of complexity to their potential health effects. This is not just a matter of scientific curiosity. It is a public health priority.

And while the science is still evolving, the message is clear: even the tiniest particles can play an important role in the complex systems that keep us healthy. That’s why projects like Imptox matter - to help us understand how these invisible intruders behave. After all, whether it’s a grilled steak or a bowl of lentils, we all want our meals to be as safe and nourishing as they can be.

Reference: Lujic, T., Gligorijevic, N., Stanic-Vucinic, D., Krstic Ristivojevic, M., Mutic, T., Cirkovic, T., Wimmer, L. & Dailey, L.A. (2025). Effects of Polypropylene and Polyethylene Terephthalate Microplastics on Trypsin Structure and Function. International Journal of Molecular Sciences. https://doi.org/10.3390/ijms26135974