Gut microbiome tests are everywhere

At-home gut microbiome tests are trending, selling insights to the curious, empowerment to the chronically ill and a claimed path to longevity to the wellness-conscious.

Private companies are offering tests, costing $100 to $500 or more, that promise a bacterial inventory of your intestines.

But can microbiome tests actually provide actionable health information?

As more patients arrive at doctors appointments with results in hand, frustrated gastroenterologists want people to know the tests have limits.

Inside our intestines, entire ecosystems of bacteria help us digest our food, absorb key vitamins, combat inflammation and much more. Research shows a healthy gut microbiome may play a role in preventing things like liver disease and diabetes and could even influence mental health.

The gut microbiome is incredibly complex and our understanding of it “is in its infancy,” said Dr. Mark Benson, a gastroenterologist for the University of Wisconsin-Madison’s health system.

“But there’s growing evidence that there are changes in the gut microbiome that are associated with different diseases, including diabetes, liver disease, obesity and inflammatory bowel disease,” he said.

There’s a key catch, though: In many cases, it’s unclear if the gut microbiome change is the cause — or an effect — of the disease.

On top of that, each person’s gut microbiome is unique, like a fingerprint. It can even vary within one person’s gut.

“Most of the variability between people, we don’t understand,” said Dr. Eamonn Quigley, the chief of gastroenterology and hepatology at Houston Methodist Hospital, who has spent 30 years researching the gut microbiome and disorders of gut-brain interactions, like irritable bowel syndrome.

In most cases, a microbiome test involves taking a stool sample, usually using a swab or a wipe for collection. The samples are mailed to a lab for analysis.

The companies then provide a report of how the person’s mix of gut microbes compares with a supposed ideal, or outlines where things are imbalanced.

These direct-to-consumer tests are not meant for clinical use and are not federally regulated, so it’s nearly impossible to say how reliable they are. Different companies can set different standards and methods for their tests.

That raises many questions for doctors: Is the sample collection consistent and reliable? What is the science behind the benchmarks they are comparing results to? Is the stool the best place from which to take a sample, or should it come from higher up in the gut?

Physicians sometimes order stool tests, but they typically are looking for specific problems: infections, inflammation from foodborne illnesses or antibiotic use, or cancer.

When patients come in with their own results from an over-the-counter test, there is little advice to give.

“If you talk to patients, these tests are appealing. They’re cool. They’re all this data,” said Dr. Sean Spencer, a physician scientist at Stanford University. The frustration for doctors, he said, is with the lack of tools to change the microbiome.

Spencer, Quigley and Benson have all had patients bring them the results of microbiome tests. But antibiotics and diet are really the only proven tools doctors have to change the gut microbiome, Spencer said.

Occasionally, the tests show a measure of inflammation in the gut or pancreatic function that can be useful to doctors, Quigley said. But beyond that, “for most people, they’re actually wasting their money,” he said.

The list of gut bugs and purported imbalances don’t align with any medically backed treatments, the doctors said.

“The technology is jumping ahead of the clinical application,” said Quigley. “Just because you can measure something doesn’t mean to say it’s worthwhile.”

The companies offering tests say they are not treating any specific conditions. But many of them — some 45%, according to a March 2024 article in Science Policy Forum — also sell supplements that they recommend to customers alongside their results.