Plastic in bile: what the research is finding

Most conversations about microplastics stop at the gut. Particles come in with what you eat and drink. Some cross the intestinal wall, most leave in stool. In, out, done.

Bile complicates that tidy story, and researchers are starting to notice.

What bile actually is

Bile is the greenish-yellow fluid your liver makes to help you digest fat. It flows from the liver into the gallbladder, gets released into the small intestine when you eat, and then, this is the interesting part, most of its acids get reabsorbed and shipped back to the liver to be used again ^[5].

That recycling loop has a name: enterohepatic circulation. Your body runs one of the most efficient recycling programs in nature every time you have a meal.

Now the question researchers are asking: what if microplastics have hitched a ride on that loop?

What's showing up in human bile

Three different research groups, using three different techniques, have now found microplastics in human bile, and, each time, the particles were more concentrated in patients with gallstones.

A 2026 study in Environmental Science and Ecotechnology analyzed bile from 14 patients during gallbladder surgery. People with gallstones had roughly four times more microplastic in their bile than people without stones. The two dominant polymers were the same ones lining beverage bottles and grocery bags, polyethylene terephthalate (PET) and polyethylene (PE) ^[1].

A separate 2025 study in Journal of Hazardous Materials used three different lab methods on 23 samples and detected microplastics in every single one ^[2]. A third group looked at 16 human gallstones directly and found microplastics in all of them, with higher amounts in patients under 50 ^[4]. In lab work from that same paper, microplastics and cholesterol clumped together into large aggregates, and mice fed microplastics on a high-cholesterol diet formed gallstones faster.

The sample sizes are small. No one has proven that microplastics cause gallstones, they may just accumulate alongside them. But three labs finding the same signal across three techniques is not nothing.

The recycling loop no one wanted to find

Getting into bile isn't the surprising part. Bile is a plausible way for the liver to take out its trash.

The surprising part is what happens next.

In a 2024 mouse study, researchers fed animals nanoplastic particles and then tracked them. Within about three hours, particles showed up in the liver, then in the gallbladder, then back in bile ^[3]. They weren't flushed out on one pass. They were cycling.

A 2026 Cell Reports paper filled in the mechanism ^[5]. Nanoplastics appear to bind to bile acids and travel the same route bile acids do, riding on a specific transporter your intestine uses to reabsorb bile for reuse. In other words, the same system that lets your body recycle bile efficiently may also be recycling plastic particles right along with it.

None of this has been measured in people yet. The recycling loop is animal evidence. But the endpoint of that loop, particles actually appearing in human bile, is now well documented.

A signal in the cells that line bile ducts

The 2026 bile study didn't stop at detection. The researchers also grew human bile duct cells (called cholangiocytes) in a dish and exposed them to low doses of polystyrene nanoplastic ^[1].

The exposed cells showed classic markers of cellular aging: damaged mitochondria, stalled cell division, and a stress signature scientists associate with tissues that have been under pressure for a long time. Melatonin, added to the dish, partially reversed the effect.

That's a laboratory finding, not a treatment recommendation. The doses were higher than what real bile contains, and dish experiments don't automatically translate to human biology. But cellular aging in the cells that line your bile ducts is not something anyone wants to see, and the field is finally equipped to start asking whether it happens in people.

Bile can also be an escape hatch

Not all the news here is bad. In human liver-and-bile-duct "organoids," miniature tissues grown in the lab, a common bile acid drug called ursodeoxycholic acid actually helped move microplastic particles into bile for excretion, and blocking bile flow made injury worse ^[6].

In that model, bile looked like an escape valve — a way to get particles out.

The full picture, then, is messier than either extreme. Bile may be part of how the body clears particles it doesn't want. It may also, at least in animals, become part of how those particles get re-presented to the gut over and over. The same fluid, playing both roles.

Notes on the science

Measuring plastic in a substance as fatty and pigmented as bile is technically difficult. The most common lab technique, burning tiny samples and analyzing what comes off, can mistake lipids and cholesterol for plastic, because they produce overlapping chemical signatures. A 2025 paper by Rauert and colleagues argues that this method needs more validation before its numbers on fatty biological samples should be taken at face value ^[7]. A 2024 study comparing 84 different labs on identical reference samples found disagreement of 2- to 10-fold on the same materials ^[8]. The bile numbers above should be read as the field's best current estimates, not settled measurements.

Where Winnow fits in

If you've been reading about microplastics and feeling like the story keeps getting bigger, you're not imagining it. Bile is one more place researchers are learning to look, and the recycling-loop possibility is a genuinely new angle on how ingested particles may behave. Winnow is a probiotic consortium whose strains have shown, in laboratory testing, an ability to bind micro- and nanoplastics within the gut lumen, the compartment where both freshly swallowed and bile-recycled particles pass through. It's one part of a broader response to a still-emerging picture, not a solution to hepatobiliary disease, and no one has yet measured whether it changes what shows up in human bile.