Estrobolome
The recycling problem.
On your gut, your estrogen, and the bloating that was never really a food story.
For years I treated my bloating like a crime scene, and food was always the suspect. Gluten one month. Dairy the next. Then it was cruciferous vegetables, then it was eating too fast, then it was some invisible sensitivity I hadn't found yet.
Long before I started this platform, I tracked what I ate. Not just the usual macros and what-not, but the various kinds of foods — think gluten, nightshades, dairy. Out of pure interest, and a little bit of stubbornness. What I found was nothing short of valuable. Gluten caused cravings, even days later. Nightshades, my body doesn't really mind. Dairy causes bloating — unless it's unpasteurised and in small quantities; pasteurised, and it sets off the cravings again. And the list goes on. Oh, and I'm allergic to eggs, something I found out isn't that uncommon, though most people don't know it about themselves. But even with my thorough N=1 research, there were things I was missing. Necessity, for one. Don't get me wrong — I learned an enormous amount about myself in that long experiment, so I don't regret a second of it, and I'd recommend it to anyone. But it was time-consuming, I won't lie.
What I kept missing was the timing. The bloating was not random. It arrived in the back half of my cycle, sat heaviest in the days before my period, and eased once I bled. I had spent so long interrogating my meals that I never asked the more obvious question: why does the same food bloat me on day 22 and not on day 8?
The answer was not in my plate. It was in the conversation happening between my gut bacteria and my estrogen, a conversation that has a name, a mechanism, and decades of research behind it. Nobody had ever mentioned it to me. It reframed the whole thing. Bloating stopped being a food story and became a hormone story, told through bacteria.
The word for what your gut does to your estrogen
In 2011, two researchers named Claudia Plottel and Martin Blaser gave this system a name. They called it the estrobolome: the collection of gut bacterial genes whose products are capable of metabolising estrogen.1 One paper, one word, and suddenly a scattered set of observations about gut bacteria and hormones had a framework to sit inside. The concept has been cited more than seven hundred times since.6
Here is the mechanism, spelled out, because the mechanism is the entire point. Your ovaries, adrenal glands, and fat tissue produce estrogen. It circulates, does its work, and then your liver packages it for disposal through a process called glucuronidation. The liver attaches a molecule to the estrogen that renders it water-soluble and biologically inactive. Think of it as a shipping label that says this one is finished, send it out. The labelled estrogen travels in bile into your intestine, ready to leave your body in stool.2
And this is where your gut bacteria intervene. Certain species in the estrobolome produce an enzyme called beta-glucuronidase. That enzyme does one specific thing: it snips off the shipping label. The estrogen that your liver had marked as finished becomes active again, and instead of leaving your body, it gets reabsorbed through the intestinal wall and travels back into circulation.3 The whole loop has a name too, enterohepatic recirculation, and it means your estrogen does not simply go out. Some meaningful fraction of it comes back.
The scale is larger than most people expect. Up to sixty-five percent of circulating estrogen is sent into the gut through bile, but only ten to fifteen percent leaves in the stool.7 The rest is recycled. Your gut is not a disposal chute. It is a sorting facility, and beta-glucuronidase is the worker deciding what gets shipped out and what gets sent back up the line.
The dial matters because beta-glucuronidase activity is not fixed. It rises and falls with the state of your microbiome. When your gut is diverse and balanced, the loop runs smoothly, recycling what is useful and excreting the rest. When your gut loses diversity, through repeated antibiotics, a low-fibre diet, chronic stress, or inflammation, the balance can tip. An overgrowth of beta-glucuronidase-producing bacteria means more estrogen gets its label snipped and sent back into circulation than your body intended.4
So where does the bloating come from
Two things are happening at once, and this is why bloating is such a confusing symptom to untangle.
The first is direct. Estrogen and progesterone receptors line your gastrointestinal tract, which means your gut is listening to your cycle whether you want it to or not. As estrogen rises across the cycle it slows gut motility, so food and gas move through more slowly, and it increases gut permeability and pain sensitivity.5 Slower transit plus heightened sensitivity is a recipe for the exact heavy, distended, tender feeling that shows up on schedule. This is the part your food diary could never explain, because the variable was never the food. It was the hormonal environment the food arrived into.
The second is the recycling loop feeding back on itself. If your estrobolome is tipped toward reabsorption, you are carrying more active estrogen than a clean disposal system would leave you with. That relative estrogen excess is associated with the cluster of premenstrual symptoms so many of us know without naming: breast tenderness, heavy or prolonged bleeding, cyclical mood shifts, and persistent bloating.4 The gut shapes the hormone level, and the hormone level shapes the gut. It is a loop inside a loop.
The naming move here is the one I keep coming back to. When bloating is framed as a food problem, the responsibility lands on you and your discipline. You must be eating the wrong thing. You must not be trying hard enough. When it is framed as a gut-hormone problem, it becomes physiology, something with a mechanism and an intervention that has nothing to do with willpower. That reframe is not semantic. It changes what you do next.
The research is decades deep. The appointment is five minutes long.
The estrobolome was named in 2011 and rests on findings that reach back to the 1980s, when researchers first measured how much estrogen the gut recycles versus excretes. The enzyme that drives it has been characterised at the molecular level. The link between gut dysbiosis and estrogen-driven conditions, from endometriosis to PCOS to hormone-sensitive cancers, is an active and well-populated field.3 This is not fringe. It is published, replicated, and sitting in the journals.
And almost none of it reaches the room where a woman describes cyclical bloating to her doctor. She is told it is normal, or stress, or IBS, or to cut out a food group and see. The framework that would connect her gut, her cycle, and her symptoms into one coherent picture exists. It is simply not offered, because the gut and the hormones are managed by different specialists who rarely speak, and the woman in the middle is left to be the connective tissue nobody paid to build.
I want to be careful here. This field is genuinely young, and honest researchers say so: measuring which bacteria you have does not yet reliably tell us what your estrobolome is doing, because many species perform the same function and one species can do many things.8 The mechanism is solid. The clinical precision is still arriving. But not-yet-precise is not the same as not-real, and it is certainly not a reason to keep sending women home with a food diary and a shrug.
What you can actually do with this
- Feed the diversity, because diversity is the regulator. Greater microbial diversity is consistently associated with better-regulated estrogen metabolism. The most evidence-backed way to build it is unglamorous and cheap: a wide variety of plants, fermented foods, and plant-diverse fibre. Not one superfood. Range. Different vegetables, legumes, and whole grains across the week do more for your estrobolome than any single supplement marketed at it.
- Fibre does two jobs here, not one. Fibre feeds the bacteria that keep the loop balanced, and it physically binds estrogen in the gut so more of it leaves in stool rather than sitting around long enough to be reabsorbed. Regular bowel movements matter for the same reason. Estrogen that lingers in the gut has more chances to have its label snipped and be sent back up. Transit time is part of the hormone story.
- Treat antibiotic courses as a known variable, not a non-event. Repeated antibiotics are one of the clearest ways to reduce gut diversity and shift the estrobolome. This is not an argument against antibiotics when you need them. It is an argument for taking your microbiome seriously in the weeks after, with fermented foods and fibre diversity, rather than assuming the gut simply resets on its own.
- Track the timing before you eliminate the food. Before you cut another food group, log the bloating against your cycle for two full months. If it clusters in the luteal phase and eases when you bleed, the variable you are chasing is hormonal, and no amount of dietary elimination will resolve a timing problem. The tracking is thirty seconds a day and it can save you months of unnecessary restriction.
- If it is severe or persistent, ask for the whole picture. Cyclical bloating alongside heavy bleeding, significant pain, or symptoms that dominate your month deserves proper investigation, not reassurance. You can ask your doctor to consider the gut and the hormones together rather than in separate silos. Bring the framework with you. Naming the estrobolome in the room is sometimes what it takes to be heard as describing physiology rather than complaining.
This is education, not medical advice. Cyclical bloating has many possible drivers, and persistent or severe symptoms deserve a real clinical workup rather than a self-directed guess.
I still notice the bloating. It has not vanished, and I am wary of anyone who promises it will. What changed is that I stopped treating it as evidence that I had failed to identify some secret food villain, and started reading it as information, a monthly report on a conversation between my gut and my hormones that I can actually influence.
The food diaries were never wrong to exist. They were just answering the wrong question. The question was never only what am I eating. It was what is my body doing with what I eat, and when, and why does the same plate land so differently across a month.
That question has an answer. It lives in the estrobolome, and it deserves to be in the appointment, not just the research paper.
If you want the fuller version of this, how the gut, the liver, and the cycle actually work as one system rather than three disconnected departments, that is a good deal of what The Art of Female Health is for. The loops are easier to see when you can watch them run across the whole book.
- Plottel, C.S., & Blaser, M.J. (2011). Microbiome and malignancy. Cell Host & Microbe, 10(4), 324–335. doi:10.1016/j.chom.2011.10.003
- Kwa, M., Plottel, C.S., Blaser, M.J., & Adams, S. (2016). The intestinal microbiome and estrogen receptor-positive female breast cancer. Journal of the National Cancer Institute, 108(8), djw029. doi:10.1093/jnci/djw029
- Ervin, S.M., Li, H., Lim, L., et al. (2019). Gut microbial beta-glucuronidases reactivate estrogens as components of the estrobolome that reactivate estrogens. Journal of Biological Chemistry, 294(49), 18586–18599. doi:10.1074/jbc.RA119.010950
- Sui, Y., Wu, J., & Chen, J. (2021). The role of gut microbial beta-glucuronidase in estrogen reactivation and breast cancer. Frontiers in Cell and Developmental Biology, 9, 631552. doi:10.3389/fcell.2021.631552
- Baker, J.M., Al-Nakkash, L., & Herbst-Kralovetz, M.M. (2017). Estrogen-gut microbiome axis: Physiological and clinical implications. Maturitas, 103, 45–53. doi:10.1016/j.maturitas.2017.06.025
- Colldén, H., et al. / Blaser group (2026). The testobolome in microbial testosterone metabolism and human health. npj Biofilms and Microbiomes, 12(9). doi:10.1038/s41522-025-00861-0
- Ilhan, Z.E., et al. (2026). Industrialization increases the estrogen-recycling capacity of the gut microbiome. PNAS, 123. doi:10.1073/pnas.2523589123 (original recycling figures: Adlercreutz & Järvenpää, 1982)
- Larnder, A.H., Manges, A.R., & Murphy, R.A. (2025). The estrobolome: Estrogen-metabolizing pathways of the gut microbiome and their relation to breast cancer. International Journal of Cancer, 157, 599–613. doi:10.1002/ijc.35427