Microbiome Tests: Genuinely Useful or Just a Passing Trend?

What your microbiome actually does for you

Your gut is home to trillions of micro-organisms — bacteria, viruses, fungi — working away quietly every single day. They break down food, synthesise essential vitamins (K, B12, B9), strengthen the gut barrier, and regulate inflammation. They even communicate with your brain via the gut-brain axis, influencing your mood and stress levels.

An imbalance in this ecosystem — known as dysbiosis — is associated with a wide range of conditions: chronic bloating, irregular bowel habits, obesity, type 2 diabetes, and autoimmune diseases. It is estimated that between 70 and 90% of chronic digestive complaints may involve some form of dysbiosis. So it's little wonder people want to "see" what's going on in there.

That's precisely what commercial microbiome tests claim to offer.

How do these tests work?

The principle is straightforward: you collect a stool sample at home, post it to a laboratory, and a few weeks later you receive a detailed report on the bacterial composition of your gut — often presented as colourful charts, complete with diversity indices such as the Shannon index.

These analyses rely on genetic sequencing of bacterial DNA found in the stool sample. This is genuine technology, widely used in research settings. The French Gut project, launched in the early 2020s by the French agricultural research institute INRAE, uses exactly this approach to analyse the microbial profiles of thousands of volunteer participants, with the aim of better understanding the links between diet, lifestyle, and health.

But there is an important distinction between scientific research and a test sold to the general public.

What these tests cannot do

France's national biomedical research institute (Inserm) is clear on the matter: commercial microbiome tests are not worth their price for everyday use. Here's why.

• A snapshot, not a diagnosis. Your microbiome changes constantly depending on what you eat, your stress levels, travel, or whether you've recently taken antibiotics. The test captures a single moment in time — not your baseline state.
• No universal reference point. There is no scientifically validated "healthy" or "unhealthy" microbial profile. Microbial diversity is broadly associated with better overall health, but no threshold exists to say definitively "you have dysbiosis."
• No guided treatment. Even if an imbalance is detected, commercial tests cannot prescribe any validated course of action. The recommendations tend to be generic: eat more fibre, cut back on ultra-processed foods — advice you'd receive regardless.
• High cost, limited benefit. These tests typically cost between £90 and £250, are not covered by any health scheme, and offer no proven benefit beyond a general nudge towards healthier habits.

When might a test actually make sense?

There are situations where a microbiome test, carried out within a supervised medical framework, may offer some exploratory value:

• Persistent digestive complaints (IBS, severe bloating, chronic diarrhoea) with no identified cause after standard investigations
• Monitoring following a prolonged or repeated course of antibiotics
• As part of a broader approach guided by a healthcare professional specialising in nutritional medicine or gastroenterology

In these cases, a test is only useful when combined with a thorough medical consultation and personalised interpretation — not when you're left alone with an online report.

If you do go ahead with a test, a few precautions are worth observing: stick to your usual eating habits for one to two weeks before collecting the sample, avoid any drastic dietary changes, and keep a note of your symptoms and meals to help contextualise the results.

What actually works for your microbiome

The good news: the most effective ways to look after your microbiome are also the most accessible — and they won't set you back £200.

• Eat a varied, fibre-rich diet: fruits, vegetables, pulses, and wholegrains nourish beneficial bacteria such as Bifidobacterium
• Include fermented foods: natural yoghurt, kefir, sauerkraut, kimchi, and kombucha all provide naturally occurring probiotics
• Limit ultra-processed foods and added sugars, which encourage pro-inflammatory bacteria
• Move regularly: physical activity measurably increases microbial diversity
• Use antibiotics sparingly: they are sometimes essential, but their impact on the microbiome is real and long-lasting

The bottom line

Microbiome tests are genuinely fascinating from a scientific standpoint, and research in this field — such as the French Gut project — opens up promising possibilities for personalised preventive nutrition. But for the vast majority of people today, investing in your diet and lifestyle will do far more good than investing in a test.

If you're struggling with persistent digestive symptoms, speak to your GP first. A thorough clinical assessment is usually worth a great deal more than a sequencing report left without proper medical interpretation.