Direct-to-consumer gut-microbiome companies cannot provide consistent results

US companies providing gut-microbiome home-testing kits can give consumers very different results. That’s the finding of researchers from the University of Maryland and the National Institute of Standards and Technology, who sent a standard stool sample to seven unnamed companies that provide direct-to-consumer gut-microbiome tests. Even though the sample itself was the same, the companies showed “major discrepancies” in their results, the paper says (Commun. Biol. 2026, DOI: 10.1038/s42003-025-09301-3). Microbiome testing faces a difficult challenge: sample consistency. If just one person submits samples to multiple different companies, those samples can differ depending on when they were collected and even what part of the fecal matter was collected, as the distribution of microbes in fecal matter is not uniform and can change over time. In other words, just one person would have no guarantee that they’re actually sending the same thing to different labs.That’s where NIST’s standard reference fecal matter comes into play. That standard has been tested to ensure it is uniform, so no matter when it is sent off to the lab, it is always the same sample being sent off.But when the standard stool was sent off, very different results came back. For example, some companies found much more clostridia, while others found more bacteroides.In a press briefing, Stephanie Servetas, one of the authors of the paper and a researcher in the Complex Microbial Systems Group at NIST, said that determining exactly what’s in the standard stool sample with enough confidence to compare it with other results is