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.

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.

Occasionally, the tests show a measure of inflammation in the gut or pancreatic function that can be useful to doctors. But beyond that, "right now, I would say this is much more for the curiosity of the consumers," said Gang Fang, who leads the Center for AI-Driven Genomic and Microbiome Medicine at Mount Sinai's Icahn School of Medicine.

"It would take much larger studies and much more rigorous designed clinical trials in order to figure out all of the mechanisms and the specific gut microbiome intervention plans that can be tailored to individuals," said Fang.

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.

One of those is Thorne, a wellness company that sells gut microbiome tests and includes recommendations for their supplements with their test results, alongside recommended lifestyle changes.

Chief Scientific Officer Nathan Price said he doesn’t see that as a conflict of interest. Customers are “not mandated” to buy anything, he said, but many are looking for solutions. Thorne's test can then track if probiotics are changing their results over time.

Probiotics and other supplements are not regulated as drugs by the Food and Drug Administration, leaving many questions about which ones work and if they even contain what they claim. Research on the potential for probiotics to treat several chronic health conditions, like atopic dermatitis, high cholesterol and irritable bowl syndrome, have yielded mixed results or limited impact.

Another company, Tiny Health, recommends supplement brands based on its own testing, but it does not sell them or get money from affiliate marketing.

The gastroenterologists who spoke to The Associated Press agreed that there is no harm in taking one of these tests if you're curious about your gut or want to contribute to a company's research.

But you can improve your gut health without the tests, the doctors said.

Instead, eat lots of plant-based fiber and protein. Improve your sleep. Move your body. See a doctor for serious gut symptoms, such as bloody stool, ongoing constipation and diarrhea or severe pain.

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP is solely responsible for all content.