If you have ever sent off an at-home gut microbiome test and wondered whether the results were real, you are not alone. A study published February 26, 2026, in the Nature journal Communications Biology suggests a lot of that skepticism is warranted.
Researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland School of Medicine blended stool from several donors into one identical sample, then sent matching portions to seven direct-to-consumer companies.
Because the biology was the same in every tube, a reliable test should have returned the same answer.
It did not. The companies reported anywhere from 34 to more than 900 microbe types, and only three types appeared in every test. One company even labeled the same sample “healthy” twice and “unhealthy” once.
Below are straight answers to the questions people ask most before trusting or acting on a gut microbiome test result.
Are At-Home Gut Microbiome Tests Accurate?
Not reliably. Researchers sent the exact same stool sample to seven companies, so a trustworthy test should have returned seven matching answers. Instead the results varied as much as samples taken from totally different people.
The number of microbe types reported ranged from 34 to more than 900, and only three types showed up in every test. The study could not crown a most accurate company either, because there is no known “correct” answer to measure against. The takeaway is simpler than that: the results disagree far too much to be trusted on their own.
Why Did Different Companies Give Different Gut Microbiome Test Results?
Because there is no shared standard. Companies collect samples differently, preserve them differently and run different sequencing technology. On top of that, each grades you against its own reference group of other people.
As Stephanie Servetas, the study’s first author at NIST, explained in a news briefing, the research can show how reproducible results are within or between companies, but it cannot reveal who was closest to the correct answer.
Can a Gut Microbiome Test Result Actually Harm Me?
It can, indirectly. Acting on inaccurate results, people have changed their diets, bought supplements they did not need or even attempted at-home fecal transplants, which carry real infection risk without medical screening.
Diane Hoffman, a professor of health law at the University of Maryland, is especially concerned about parents of autistic children. “If parents are restricting the intake of certain nutrients [based on these recommendations], this can be harmful for the child,” she said.
Should I Take Probiotics or Gut Health Supplements Based on My Score?
Be cautious. Your score depends on which company tested you, so the same gut can look “healthy” to one lab and “unhealthy” to another. It can also vary within the same company. That is a shaky basis for changing your diet or adding gut health supplements.
Talk to a doctor before acting on a result, especially when a product is being recommended by the same company that flagged the problem.
Can I Trust a Gut Microbiome Test Company That Also Sells Supplements?
Treat that setup with extra skepticism. Some companies sell supplements alongside the test, and the issue the test finds tends to match the product they sell.
Scott Jackson, the study’s corresponding author, put it bluntly: “It just so happens that the thing that is wrong with your microbiome happens to complement the product that they also sell.” His advice to consumers is “buyer beware.”
What Should I Do Instead of Trusting an At-Home Microbiome Test?
Treat the gut microbiome test results as a curiosity, not a diagnosis, and bring any real symptoms to a physician.
Jacques Ravel, a professor of medicine at the University of Maryland School of Medicine and a study author, urges caution: “You should be very careful in interpreting what companies are telling you. Especially be very cautious when they start recommending any kind of treatment or any kind of supplement or anything they [want to] sell you.”
