Direct-to-consumer microbiome tests don’t work as advertised

In 1904, Elie Metchnikoff, a key figure in modern immunology, gave a talk at the Pasteur Institute in Paris proposing that harmful gut bacteria cause aging. He suggested consuming yogurt to counter this effect, as the people from a Bulgarian region known for longevity ate yogurt with beneficial bacteria. Misinterpretation by a journalist led to a yogurt craze as an anti-aging remedy.

Since then, our understanding of the microbes living inside us has expanded, highlighting their importance to human health. Still, expectations remain unreasonably high. Scientists admit there’s still much to learn about applying this knowledge of the microbiome to improving human health. Nonetheless, many companies now offer direct-to-consumer (DTC) microbiome tests for people seeking solutions to various health issues.

In a recent article published in Science magazine, several legal and medical experts argue that DTC microbiome tests need increased regulation. Regarding the U.S. market, the article contends that the “companies’ claims of having the ability to detect ‘abnormal’ microbiomes are not substantiated by research; the testing processes lack analytical validity, and the results have no demonstrated clinical validity.” The tests need more government oversight to safeguard consumers from potential harm.

Sequencing techniques are used to analyze samples, often fecal matter sent by mail, to identify the microorganisms present in the intestine, their abundance, and sometimes their metabolic functions. After a few weeks, customers receive a report describing their microbiome’s state, categorized as healthy or ill. This assessment is based on comparing a customer’s microbiome to that of other healthy individuals or people with certain health conditions. However, due to the limited data in the companies’ databases, the information may not be fully representative, and the comparisons may not be very informative.

“Products are being launched to analyze the microbiota and look for any imbalances known as dysbiosis, but the big issue is that there’s no universally validated technology for this yet,” said Francisco Guarner, a gastroenterologist and member of the scientific committee of the International Human Microbiome Consortium. “Many technologies are available, but the lack of clear markers complicates clinical decisions. Doctors rarely order these tests, leaving it to dietitians or alternative medicine specialists. Reports, often lengthy and confusing, are created to justify the expense without offering validated interpretations of the markers. This can leave patients bewildered and doctors unsure how to proceed.”

The research team led by Diane Hoffmann from the University of Maryland noted that about 45% of the companies selling microbiome tests also sell supplements recommended to consumers based on test results. They also suggest repeat tests to see if these supplements and dietary changes have affected a customer’s microbiome.

Analytical validity issues arose when different labs produced different results from the same sample. Occasionally, a laboratory yielded varying results when analyzing the same sample sent separately. These discrepancies could stem from sample handling, software discrepancies and analysis technologies. Despite having reliable analysis systems, defining a healthy human microbiome remains a point of contention.

“Different microbiotas can be healthy, and there’s significant variation among individuals. Each person’s unique story means they have a distinct microbiota,” said Fermín Milagro, director of the precision nutrition line at the University of Navarra’s (Spain) Nutrition Research Center. In his opinion, the test data could be useful “to identify an enormous dysbiosis or if there are three dominant species of microbiota. Perhaps if the prices were cheaper, a customer could conduct several tests to see if a treatment is having an effect on a specific parameter of interest. But they’re not going to predict your risk of Alzheimer’s in the next decade. In short, these tests have useful applications when interpreted by trained professionals, and not when customers are sent incomprehensible reports.”

Microbiome analyzes, with clear objectives and expert interpretation, are also advocated by researcher Nuria Malats from Spain’s National Cancer Research Center (CNIO). In a study published in BMJ Journals, Malast linked 17 gut microorganisms to pancreatic cancer risk. This approach aims to detect the cancer early, but further validation is needed for clinical use. Malats concurs with Hoffman’s view on direct-to-consumer tests. “They are too premature. They’re like genetic tests that reveal the presence of a certain gene, but what does that really mean? And this is even trickier because genetic tests remain constant throughout life, but the microbiome is always changing.”

Experts agree on the need for better regulation. Neither the European Medicines Agency nor the U.S. Food and Drug Administration (FDA) currently control these DTC tests. Diane Hoffman and her team wrote that while companies often include a disclaimer that their tests are not diagnostic, some marketing claims can mislead consumers into believing the results are scientifically accurate and medically relevant, which may not be the case. The risks of unreliable information include erroneous self-diagnosis and substituting supplements for medications prescribed by professionals. In Francisco Guarner’s opinion, “They’re a waste of money.”

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