Two UCLA Health physicians told readers of their Ask the Doctors column on 24 August 2026 that consumer gut microbiome tests are not worth the money. Dr Eve M. Glazier and Dr Elizabeth Ko wrote that the science is not settled enough to support the personalised readouts these services sell, saying that "currently, there is no agreement on what makes a healthy gut microbiome" and that "it is not clear whether this kind of personal assessment is even possible". They pointed to a finding that the same stool sample sent to different companies came back with very different microbiome profiles and different advice. The column is an opinion piece by practising clinicians rather than a regulatory position, and it addresses the US market, though similar direct-to-consumer kits are sold in the UK. Their own suggestion was to put the money towards fibre-rich plant foods, fermented foods, physical activity and sleep.
What the testing study actually found
The inconsistency the column refers to was measured by researchers at the National Institute of Standards and Technology and the University of Maryland, Baltimore, published in the journal Communications Biology on 26 February 2026 and reported by Science News. NIST blended bowel movements from several people into a single standardised reference material and sent three identical portions to each of seven direct-to-consumer testing companies. Science News reported that the differences between companies were similar in scale to the differences expected between samples from different people, and that one company labelled two replicates healthy and a third unhealthy. The researchers were explicit about the limit of the method: it shows how reproducible results are, not which company is closest to correct.
What this means for your supplement routine
None of this says the gut microbiome does not matter. It says the commercial tests sold to measure it do not agree with one another, so a report that names your bacteria and then recommends specific products is resting on an unstable measurement. Science News noted the concern that people may end up taking probiotics they do not need on the strength of such a result. If you are deciding where health money goes, that is a reason to read a test report as a marketing document rather than a diagnosis, and to look instead at what you are paying across your regular supplement order.
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This article reports published news and research and is for information only. Food supplements are not a substitute for a varied diet or medical care, and no product mentioned is intended to diagnose, treat, cure or prevent any disease. Speak to your GP or pharmacist before changing what you take, especially if you are pregnant, breastfeeding, or taking prescribed medicines.