Home Gut Microbiome Tests Give Varying Results
June 24, 2026
By:Stephanie Servetas
Credit:
Megan King/NIST
Editor’s note: This blog post discusses the scientific study of fecal matter (aka poop). If that’s bothersome to you, you might want to skip this one (or at least not read it while eating).
You may have heard about companies that claim they can give you lifestyle advice by analyzing a stool sample, similar to how you can decode your DNA with saliva
A team of microbiologists at NIST recently put these tests … well … to the test using precisely measured stool samples we already had in our labs
Microbiome Mysteries
The gut microbiome is a collection of microbes — such as bacteria, fungi and viruses — that live in our gastrointestinal tract. The microbiome can’t be easily checked while it’s inside your body, but it can be analyzed from a stool sample
It’s important to understand just how challenging it is to learn about a person’s microbiome. You can’t just put a stool sample under a microscope and figure out what’s happening in the body
The reality is that preparing and studying a sample is a complex, multistep process. At any point, it’s easy to accidentally take a step that might affect the accuracy of your results, which we call introducing bias
Another significant challenge is that our gut microbiomes are very different from person to person, so there’s no “normal” gut microbiome that scientists have been able to pinpoint. In addition, the microbiome does not exist by itself in your stool — undigested food, bacteria, dead cells and other things also reside in a stool sample
Credit:
Shobujsk/Shutterstock
A gut microbiome test is different from a medical test you may be accustomed to, such as a blood test. In an iron blood test, for example, physicians know what they’re looking for and how much they should find. They conduct the test and check if your results fall within a specific range. These tests have existed for many decades, with standardized methodologies for conducting them
Microbiome science, in contrast, is quite new. The field is only around 20 years old, and there’s still so much that researchers are learning about this complex and interesting part of our bodies. Microbiome researchers don’t have the technology and the research knowledge to say, “Yes, this is 100% what we were expecting to find in your microbiome.”
Testing the Test
In our recent study, we sent identical stool samples from one donor, which we’ve already studied and understand very well, to seven different microbiome test companies. This was an anonymous test, so the companies didn’t know they were being researched
The results we received were quite different, even though the companies received identical samples. One company, for example, marked a sample as having an “unhealthy” gut microbiome, while none of the other companies did
The likely reason for this is the bias issue I mentioned above. Different labs are handling samples differently, introducing varying levels of bias
What Our Results Mean for Consumers
This variability in results doesn’t mean I would advise people not to take these tests. In fact, I may try one myself one day. The reason I haven’t done so yet is simply because, in addition to being a researcher at NIST, I’m a mom of two young children who keep me pretty busy
When my kids are older, I actually think it might be interesting and fun to have our entire family take one of these tests and see how our gut microbiomes are similar and different, given that we live together and eat a lot of the same foods. (That’s a microbiologist’s idea of fun anyway.)
If you take a test, I encourage you to approach the results you receive with a healthy dose of skepticism
I also wouldn’t make major lifestyle or dietary changes without consulting your doctor. Your physician knows you, and they can order more scientifically rigorous testing, such as a blood test, if you need more information based on something found in your gut microbiome. As a microbiologist, I generally know how microbes interact with the body but not necessarily how the body responds to microbes. I defer to my doctor’s guidance and would still do so, whatever the results of a microbiome test might tell me.
Standard Reference Fecal Material
You may be wondering why we had precisely measured fecal matter samples available to us in our lab. That’s because NIST produces and sells standard reference fecal material for microbiome research. These reference materials are used to improve our understanding of the medical research behind treatments such as fecal transplants (yes, that is exactly what it sounds like). Fecal transplants have been shown to help treat gut conditions like colitis and, impressively, may also improve patients’ responses to cancer treatment.
When we created this standard reference material, we had leftover samples from individual donors that we didn’t include in the reference material. But we’ve measured the material so thoroughly that it was perfect for this research
Future Steps in Microbiome Testing Research
For areas such as microbiome research, a key step is to progress the measurement science to better understand where these measurements may be going awry. My group at NIST has been working to understand this complex science for about a decade
We contacted the companies after our study was completed, and most were happy to work with us on future research. As a result, we are now collaborating with researchers in the microbiome testing field to improve these measurements — and confidence in the results. Our ultimate goal is to help these tests become more like a blood test, so they can potentially be part of your regular health screenings. This could help us all become healthier through personalized medicine.
Bioscience,
Chemistry and
Metrology
About the author
Stephanie Servetas is a microbiologist at NIST. Stephanie’s research focuses on the development of laboratory-grown, reproducible microbial communities that can serve as tools for the development of next-generation, sequencing-based diagnostics, pathogen detection and microbial therapeutics (bugs-as-drugs). She received her bachelor’s degree in biotechnology from the Rochester Institute of Technology and a Ph.D. in emerging infectious diseases from the Uniformed Services University of the Health Sciences.
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