How do microplastics impact our gut health?

Figuring out what kind of plastic a person or animal has consumed is “something that always sounds easier than how it is in reality,” Gloria Fackelmann, a microbial ecologist at Italy’s University of Trento, told EHN. Scientists use specialized devices to analyze the wavelengths of light that bounce off a given piece of plastic, and compare it to databases created by other researchers. This process is imperfect, Fackelmann said, because something as basic as the plastic’s age can alter how it reflects light.

Adding to the complexity is shape and size. A grain of plastic visible to the naked eye behaves far differently from a nanoscale particle that’s the size of a virus. Multiple studies have shown that the smallest plastics can pass from the gut into the blood, and from there into the brain, placenta, liver and other organs. And the smaller something is, the more surface area it has, increasing a plastic particle’s ability to glom onto cells and leach a higher dose of chemical additives. Body-Malapel said nanoplastics are so miniscule that there is currently no way to detect them in human tissues.

Researchers can’t feed human volunteers plastic-peppered food and see what happens. Instead, they must pursue a variety of indirect routes: analyzing human feces, creating artificial stand-ins for digestive organs, using lab animals, or looking at wild creatures in plastic-polluted environments.

Plastic in birds

In her most recent study, published in March in Nature Ecology & Evolution, Fackelmann and her collaborators looked at how microplastics affected the gut microbiomes of two seabird species, Northern fulmars and Cory’s shearwaters.

The team measured bacteria in the birds’ stomachs and cloacas, and flushed out their digestive tracts to count and weigh the microplastics inside. The birds with more individual pieces of plastic had a higher diversity of bacteria, while those with a greater weight of plastic had lower diversity. Greater diversity isn’t always beneficial, Fackelmann said. “Maybe you have more microbes, but the excess are all pathogens, in which case, that wouldn't be good.”

This finding “lends some credence to the idea of plastics as a vector” for bacteria, she added. Bits of seafaring plastic are thought to accumulate bacteria, which then make a home in a bird’s stomach and intestines. As the researchers discovered, these bacteria weren’t a representative sample of what’s normally found in seawater. Instead, there was a preponderance of plastic-eating microbes, along with antibiotic-resistant and disease-causing bacteria.

While the team didn’t assess the seabirds’ health, the microbial shift suggests this petrochemical diet is doing the birds no favors. “The very fact that we were able to measure the effects of microplastics on the gut microbiome in this natural system, using just naturally found concentrations of microplastics,” Fackelmann said, is “striking.” She added: “I wouldn't be surprised if the situation were to be similar for humans.”

Artificial organs, real problems

In France, a team of researchers took a radically different approach. Unable to directly observe microplastics in a living person’s gut, they devised a fermentation chamber to mimic the conditions in the large intestine. The team seeded the fermentation chamber with donated poop, and fed the resulting bacterial ecosystem with nutrients and vitamins. “It does smell a bit,” study author Lucie Etienne-Mesmin, a microbiologist at Université Clermont Auvergne, told EHN. “After a while you get used to it.”

Every day for two weeks the team dosed the system with tiny beads of polystyrene — the most common type of plastic — and measured changes to the artificial gut. Per the study, published in January in the Journal of Hazardous Materials, beneficial bacteria declined, while two disease-associated strains increased, as did the production of skatole, the substance that gives feces their nose-wrinkling odor.

Notably, the study’s authors say, these changes mirror what medical researchers see in inflammatory bowel diseases such as Crohn’s and celiac, where the body’s immune system mistakenly attacks healthy gut cells. Many factors are likely to blame for the global rise in bowel diseases, from air pollution and ultra-processed food to antibiotic overuse.

However, this study, and several others like it, suggest that microplastics may also have a role.

A 2021 study from China’s Nanjing University, for example, found a correlation between the severity of a patient’s inflammatory bowel disease and the number of plastics in their feces. A Tufts study published this June, which utilized 3D intestinal cell cultures called organoids, found that plastic exposure prompted cells to secrete inflammatory molecules.

The French researchers cautioned that it was only a preliminary study, meant to guide more research. Still, Etienne-Mesmin said, the results warrant concern, particularly because harmful changes were seen after only two weeks. “In real life, you are exposed on a daily basis,” she said. “So maybe the effect will be even stronger than the one we observed.”

Plastics and obesity 

The use of pristine plastic beads, such as those used in the French study, are a “good starting point,” Demokritou said, but he cautions that their utility is limited, particularly from the perspective of regulators and health agencies. “We need to use more environmentally relevant microplastics, the ones that you and I consume in our food and the water we drink,” he said. “Otherwise, it's a dangerous thing to generate data that may or may not be relevant to human health.”

Demokritou and his colleagues are developing ways to shorten 40 or 50 years of plastic degradation down to a few weeks through incineration and other methods. Evidence suggests that this process, called weathering, induces physical and chemical changes that can make plastic more dangerous. An August study from South Korea’s Daegu Gyeongbuk Institute of Science and Technology, for example, found that weathered microplastics induced noticeably more brain inflammation than their pristine counterparts.

In a study published this March, Demokritou’s team applied a slurry of weathered nanoplastics to a cell culture of a human intestinal wall. The team then ‘fed’ the cells a high-fat solution and discovered that the microscopic plastics increased fat digestion by 33% and fat absorption by a whopping 145%. Plastics and intestinal membranes are both hydrophobic, meaning they repel water, Demokritou said. Their hydrophobic nature means plastics and gut walls stick together when paired up, sandwiching any fat molecules in between, and increasing both the time and surface area for the fat to be absorbed.

The study also found that microplastics triggered the cells to release inflammatory molecules, similar to what the Tufts study identified. “If you have inflammation, it makes the gut leakier,” Demokritou said, explaining that increased intestinal permeability means greater amounts of any toxic substance we swallow can enter the body. A leaky gut is linked not only to inflammatory bowel disease, but also to allergies, asthma, autoimmune disorders and obesity.

Demokritou’s study isn’t the only research to suggest a link between plastic and obesity. A 2021 National Institute of Environmental Health Sciences review identified several ways that microplastics might be making us fatter, including altering the immune system, changing organ function and disrupting hormones. These risks come not just from the plastic itself, but from the synthetic chemicals and heavy metals that plastics can contain.

How to avoid eating microplastics 

There are a few common sense ways to reduce dietary exposure to plastics, such as swapping out plastic cookware and food containers for metal, glass and ceramic. But even the most assiduous plastic-free practitioner can only do so much. After 50 years of dumping plastic waste into the environment, followed by their degradation into ever-smaller pieces, every corner of the planet is now seeded with these pernicious particles. “They are in the air you breathe, the water you drink, the food you eat,” Demokritou said. “So, I hate to say, it's not easy to control your exposure.”

Until governments and corporations take drastic action to cut plastic production and waste, everyone on Earth, even in remote Arctic regions, will continue to eat a side of plastic with every meal. Demokritou highlighted the need for science-based plastic legislation, better waste management strategies and the development of safe, biodegradable alternatives to conventional plastics. “We cannot go back to the Stone Age. Plastics are our life,” he said. “We need to attack this kind of problem from all angles.”