You may be familiar with the scene. You’re talking to a new patient or client—or a stranger on the street who has a “quick” question for you—and they want to know if the microbiome test they took last month can really tell them how and what to eat. You take a deep breath and consider how to best answer this question.
The exploding market for at-home gut and/or vaginal microbiome tests suggests no shortage of consumer interest in digestive and reproductive health and personalized diet recommendations. Although the evidence supporting the tests’ ability to provide clinically appropriate and comprehensive individualized nutrition guidance is woefully lacking, can these tests potentially map the microbiome in ways that inform high efficacy custom probiotic blends or other helpful insights influencing the work that dietitians do? Let’s explore.
Who Offers the Tests?
Direct to consumer (DTC) or at-home microbiome testing kits are sold by a wide range of companies globally. The University of Maryland, Baltimore, put together a report in December 2023, identifying 31 different companies worldwide selling these products.1 Of the 31 identified companies, nearly half of them also sold supplements and included specific recommendations for these supplements in their test results and feedback to the consumer. The report also found that, of the companies operating out of the United States, only 12 of 27 claim to use labs that abide by Clinical Laboratory Improvement Amendments of 1988 regulations, which include federal standards applicable to all US facilities or sites that test human specimens for health assessment or to diagnose, prevent, or treat disease.2
These testing kits typically range in price from $120 to $400 and include a report showing a snapshot of the types of microbes present in the submitted sample at the time of collection. Many companies also provide diet or nutrition recommendations, although there’s a lack of evidence to support this practice. Some companies also offer specific types of probiotics to help correct supposed microbiome imbalances. Importantly, these tests are not regulated in the same way as FDA-approved lab tests.3
A Critical Eye on the Science
Over the last decade, the human gut microbiome has been linked to a multitude of disease states and conditions including mental illness, cancer, insulin resistance, and obesity, among many others. However, as authors in a newly published study in Communications Biology point out, despite extensive research utilizing metagenomics for microbiome characterization, there are currently no regulatory-approved clinical microbiome diagnostic tests in the United States.4
The authors of this study set out to assess the current state of DTC microbiome tests by evaluating the performance of seven DTC gut microbiome testing services using National Institute of Standards and Technology (NIST)—developed and standardized human fecal material. Three kits were ordered from each company to assess the intra-and interlaboratory precision. Collection procedures were followed according to instructions provided by each company, where the same homogenized NIST-standardized human fecal sample source was used for all tests. Results, in the form of company-specific reports, were received anywhere from two to eight weeks following shipment of the sample. Taxonomic profiles were manually extracted from these reports by the researchers and used for all subsequent analyses. To avoid any procedural biases, the companies were not informed of the ongoing assessment until after all the samples had been processed and final reports were received by NIST.4
Results revealed major discrepancies, both within and across the different service providers. Significantly, study authors found variability between providers was on the same scale as biological variability between different donors. They attribute the observed differences to methodological variability and lack of sufficient quality control.4
As part of its mission to promote US innovation and industrial competitiveness, NIST works with stakeholders in industry, academia, and other government agencies to develop standards to support the advancement and commercial translation of microbiome science. A primary concern with the DTC microbiome tests, these researchers say, is that the at-home tests do not undergo the same rigorous oversight in validating analytical performance as traditional medical diagnostic tests. Such validation is crucial to assure clinicians, patients, and regulators of the reliability and actionability of test results. This lack of validation and the implications may critically not be apparent to the consumer.4
“Analytical performance is a prerequisite for making sound clinical recommendations. Our results demonstrate the need for standards to ensure analytical validity and consumer confidence,” the authors say.4
The Lancet Gastroenterology & Hepatology published an international consensus statement on microbiome testing in clinical practice in 2025. This statement was the result of extensive analysis and review by an international multidisciplinary expert panel established to standardize best practices of microbiome testing for clinical implementation. It addressed areas such as the following5:
- recommendations on general principles and minimum requirements for provision of tests;
- indications for use of tests;
- pretesting protocols;
- methodology of analyses;
- reporting of results;
- potential clinical value;
- current knowledge gaps and future directions; and
- a suggested regulatory framework to minimize the use of inappropriate tests and pave the way for the evidence-based development and use of human microbiome diagnostics in clinical medicine.
The task force stated that “qualitative or quantitative data retrievable from microbiome reports may be helpful in clinical practice, although there is still insufficient evidence to apply them in clinical practice.” They also discouraged the suggestion of therapies, including dietary interventions, by the reports to avoid patients going outside the bounds of evidence-based clinical medicine and nutrition.5
The Takeaway for RDs
Microbiome measurements are impacted by a vast number of methodological variables including sample collection, storage, and shipping methods; nucleic acid extraction techniques and sequencing technology; and bioinformatic analyses. As prominent researchers in the field point out, bias can be introduced at every step, and even minor changes in methodology can lead to significant differences in results.4
It’s not unreasonable to believe that certain types of standardized, quality-controlled microbiome tests may one day be a helpful clinical tool used to guide evidence-based treatment, including customized MNT. But we aren’t quite there yet. Until then, RDs can do what they do best: communicate the nuance and what is known or unknown about the current state of the art. Dietitians frequently field questions from patients, clients, and consumers about many emerging products like DTC microbiome tests marketed to address perceived microbiome and nutritional imbalances. Approaching these individuals with empathy, communicating our interest in understanding the reasons behind their pursuit of these tests, and establishing ourselves as trusted resources in conveying the limitations of the current evidence as well as sharing ideas about additional evidence-based options available to help them meet their goals is what RDs can excel at.
— Heather Davis, MS, RDN, LDN, is editor of Today’s Dietitian.
References
1. Summary information about DTC microbiome-based testing companies. University of Maryland, Baltimore website. https://www.law.umaryland.edu/media/sol/sol-2022-images-and-files/academics/programs-and-centers/health-law-program/pdfs-docs-and-files/DTC-Microbiome-Testing-Companies—as-of-3-2024.pdf. Published January 2024. Accessed March 15, 2026.
2. Clinical laboratory improvement amendments. CDC website. https://www.cdc.gov/clia/php/about/index.html. Published September 11, 2024. Accessed March 12, 2026.
3. Aggeler M. Are at-home gut microbiome testing kits a scam? The Guardian. July 5, 2024. https://www.theguardian.com/wellness/article/2024/jul/05/whats-a-gut-microbiome-test
4. Servetas SL, Gierz KS, Hoffmann D, Ravel J, Jackson SA. Evaluating the analytical performance of direct-to-consumer gut microbiome testing services. Commun Biol. 2026;9(1):269. 5. Porcari S, Mullish BH, Asnicar F, et al. International consensus statement on microbiome testing in clinical practice. Lancet Gastroenterol Hepatol. 2025;10(2):154-167.