Hormones feel like they belong to other parts of the body: the brain, the ovaries, the adrenal glands. But a growing body of research points to an influence on all of them from an unexpected place, the community of microbes living in your gut. This page is an educational overview of what that research describes, graded by how well established each connection is, and where a live L. reuteri yoghurt fits into a gut-focused routine.
This is the clearest and best-established of the gut–hormone connections, and it even has its own name: the estrobolome, the collection of gut bacteria capable of metabolising oestrogen.
The mechanism is well documented. After the body uses oestrogen, the liver packages it up for removal and sends it to the gut. There, certain bacteria produce an enzyme called beta-glucuronidase, which can unpackage that oestrogen and allow it to be reabsorbed into circulation rather than excreted. In other words, the makeup of your gut bacteria helps determine how much oestrogen stays active in the body.
When this bacterial community is balanced, oestrogen recirculation tends to stay in a healthy range; when the microbiome is disrupted, that balance can shift. This is why researchers increasingly study the estrobolome as a factor in oestrogen balance, particularly in women's health.
Cortisol is the body's primary stress hormone, governed by the HPA axis (the signalling link between the brain and the adrenal glands). The connection between this stress system and the gut is one of the most heavily researched areas in the field, and it runs in both directions.
The gut and brain are in constant communication, partly through the vagus nerve, a direct physical line between the two, and partly through compounds gut bacteria produce, such as short-chain fatty acids. Through these channels, the state of the gut microbiome has been studied for how it may influence the body's response to stress and its regulation of cortisol.
Some of the most striking evidence comes from studies in animals raised without any gut bacteria, which show altered stress responses that can be changed by introducing microbes. It is a strong illustration of how foundational the gut appears to be to the body's stress machinery, though, as with much of this field, translating it precisely to humans is ongoing work.
Serotonin is often called the "happiness molecule", but the story is more interesting than that nickname suggests. The large majority of the body's serotonin is produced in the gut, not the brain, and gut microbes play a real role in that production by influencing the specialised cells in the gut lining that make it.
The serotonin made in your gut works mostly in the gut and body, regulating processes such as digestion, and it does not simply travel up to the brain. So the popular shorthand of "fix your gut to boost your mood" oversimplifies the science. What the evidence supports is that the gut is the body's main site of serotonin production, and that the gut–brain axis is being studied for how it influences signalling relevant to mood and wellbeing.
This is the least settled of the connections on this page, and it deserves to be presented as such. Research has begun to identify associations between gut microbiome composition and testosterone levels, and some studies suggest particular bacteria may interact with androgen metabolism.
The important qualification is that much of this work is still early, largely from animal studies, and associational rather than established cause and effect in humans. It is a genuinely promising area, and one worth watching, but it would be insincere to present it as settled in the way the oestrogen or cortisol links are. We include it because it is part of the picture, and we would rather tell you where the science is thin than overstate it.
Look across these systems and a pattern emerges. Oestrogen recirculation, stress regulation, serotonin production, and possibly androgen metabolism are each shaped, to genuinely varying degrees, by the state of the gut microbiome. The common factor is not any single hormone; it is the balance of the bacterial community in the gut.
This is why gut health is so often described as foundational. It is not that the microbiome is a lever for any one hormone, but that a balanced gut is part of the environment in which the whole system functions well, the same balance our strains are studied in connection with (see our theory of gut dysbiosis).
The consistent message across this research is that a balanced gut microbiome is the sensible foundation. Our yoghurts are live L. reuteri yoghurts, fermented fresh, at over 100 billion live cultures per bottle, lactose-free and with no added sweeteners, made for people who want to support their gut as part of a healthy routine. We make no claim that they balance hormones or treat, cure or prevent any condition. If hormonal health is your interest, gut health is one researched piece of a bigger picture that also includes diet, sleep, stress, and professional medical advice where needed.
Independent research on the gut–hormone connections described above:
Important: this page is educational information only. It is not medical advice, and it is not a claim that our yoghurt balances hormones or treats, cures or prevents any condition. Several of the connections described are at an early, associational, or animal-research stage, and we have tried to say so clearly. If you have concerns about your hormones or health, please speak with a qualified healthcare professional. Original studies are available via PubMed and other open scientific databases.
Read about our strains and the science, our theory of gut dysbiosis, the gut–skin axis, or browse the yoghurt in our shop.