We all have a gut microbiome — a complex community of trillions of microbes living in our digestive tracts. Researchers are still figuring out all the different ways these organisms affect our health, but the science suggests that they play a role in many physiological processes, including our ability to fight cancer and maintain good brain health.
Perhaps because of this important, burgeoning understanding, there has been an influx of companies selling “direct-to-consumer” microbiome tests. These tests claim to provide a detailed view of the microorganisms that reside in your gut and use that information to prevent and reverse disease.
Much like food sensitivity tests, direct-to-consumer (DTC) gut microbiome tests are quite popular, and investors have been shelling out cash in hopes of getting in on the action. In 2020, Crunchbase reported that between 2015 and 2020, health startups focused on the gut microbiome raised $1 billion in venture capital funding. But do current microbiome tests actually do what they claim to do?
What is the gut microbiome?
The gut microbiome is comprised of microorganisms including bacteria, viruses, and fungi that live in our digestive tracts. Collectively called the microbiome, these organisms work together to maintain the health of the gastrointestinal tract.
This is “essentially a universe of microscopic life that we’ve evolved to harbor in our gut that help extract nutrients from our food, and help fight off infections by both training our immune system and directly competing with infectious microbes,” Ivan Vujkovic-Cvijin, assistant professor in Cedars-Sinai Divisions of Biomedical Science, Gastroenterology, and the F. Widjaja Inflammatory Bowel and Immunobiology Research Institute, tells Inverse.
Research suggests that disruptions to the microbiome “may profoundly influence our susceptibility to inflammatory diseases, things like autoimmune disease, liver disease, heart disease, neurological diseases, and even cancer,” Vujkovic-Cvijin says.
What microbiome tests can, and can’t, do
It’s understandable that people would want to know how their microbiome might be affecting their health, and that’s exactly what companies selling microbiome tests are counting on.
Andrea Love is an immunologist and microbiologist who works as an immunology consultant for the biotech industry and co-hosts the Unbiased Science podcast. She cautions that we shouldn’t conflate research with clinical applications. For example, research shows that a diversity of microbes in the gut is generally good, but that doesn’t mean doctors know enough to make specific dietary recommendations based on a microbiome test.
“A clinician’s job is to be a patient care provider, whereas a scientist’s job is to do the science that's ultimately going to be the foundation for patient care,” she tells Inverse. “Just because we are learning things through research doesn’t mean we have the clinical applications of that research yet.”
Unfortunately, clinical applications are what microbiome tests claim to understand.
When you take a microbiome test, you collect a stool sample at home and then send it to the company to have it analyzed by a lab. The results may give you a profile of some of the components of the microbiome, typically the types of bacteria that are present.
“In some cases, they’re extracting the DNA, which is the genomic material, in other cases, it may be the RNA, which is the expressed genes [of gut microbes],” Love says. “And they look at that and make some sort of conclusion.”
Love says we don’t yet have the information to accurately say, “‘I took the stool sample, and I see these populations, therefore, it means X.’”
Amy Barto, an associate professor of medicine at Duke and the director of its fecal microbiota transplantation program, agrees. “We have yet to determine an ideal blueprint for the gut microbiome, which is very dynamic and differs due to many factors, including underlying [gastrointestinal] conditions, age, diet, and region of the world, to name a few,” she says. “As such, it can be difficult to predict risk for certain diseases based on one snapshot analysis.”
In fact, our gut microbiome is changing all the time based on a variety of factors, including the food we eat, our hormones, and even some medications. These changes are also individual and can vary person to person. We simply don’t know enough about our gut microbes to extrapolate from the results of a microbiome test what a person should be eating, though that’s exactly what these companies are trying to do.
“While these tests can provide a detailed profile of the different components of the microbiome, we still do not have targeted therapies to manipulate various aspects of it,” Barto says.
What’s more, Love says, you’re only getting a partial snapshot.
“These at-home tests are really only looking at a very small proportion of the scope of bacteria in your stool sample. For example, some bacteria may be better at adhering to the gut, and they're not going to shed in the feces,” she says. “And so it's not necessarily an accurate picture of even what's happening in your gut, even though it is a product of your gut.”
Perhaps the most significant point about these gut tests is that they currently don’t provide any information doctors can’t glean through other means. Doctors already have a variety of tools to diagnose, prevent, or treat many diseases, Vujkovic-Cvijin says, and microbiome tests currently can’t tell patients anything those other diagnostic tools can’t.
“Testing one’s microbiome currently will not reliably tell you more than the routine tests that are already being performed by doctors,” he says. “There are many studies that report certain microbiome patterns are associated with certain diseases, but these patterns are also seen in healthy individuals to a great extent and are often driven by unrelated variables like age, sex, and lifestyle behaviors.”
That may be one reason not a single microbiome test is FDA-approved.
The future of microbiome testing
Currently, microbiome tests can’t accurately tell you what you should or shouldn’t be eating, but that may change down the road.
“I think personalized nutrition to affect our health through the microbiome is a very real future possibility,” Vujkovic-Cvijin says. He cites work from Eran Segal that has used large human diet studies and machine learning to build an algorithm that can tell individuals what foods increase their own chances of developing type 2 diabetes so that they can be avoided.
“The framework Dr. Segal’s group has laid is an excellent example of how DTC microbiome tests can use data-driven experimental approaches to impact human health,” he says. “A key feature of their work that makes it valuable is that they tested their approach rigorously on individuals that their algorithm hadn’t seen before.”
Before we can trust any dietary recommendations based on microbiome tests, they’d need to go through a similarly rigorous testing process.