The Estrobolome: How Gut Bacteria Affect Your Estrogen

What is the estrobolome?

Your gut holds trillions of bacteria that help digest food and make vitamins and other compounds (NIDDK). The "estrobolome" is the subset of those bacterial genes that can metabolize estrogen. Researchers proposed the term in 2011 as part of a model for how gut microbes might influence diseases far from the gut, including hormone-sensitive cancers (Plottel and Blaser 2011).

How do gut bacteria affect estrogen?

Step by step

How gut bacteria recycle estrogen

1. 1Estrogen circulates and does its work.Before menopause most comes from the ovaries; after menopause, mostly from fat tissue.
2. 2The liver packages it for removal.It attaches a molecule (glucuronide) that inactivates estrogen and makes it water-soluble, then sends much of it into bile and the intestine.
3. 3Gut bacteria can unpack it.Some bacteria make beta-glucuronidase, an enzyme that removes the package and turns estrogen back into its active form.
4. 4Reactivated estrogen can be reabsorbedInto the bloodstream rather than leaving in stool. This loop is called enterohepatic recirculation.

Lab studies confirm that specific gut bacterial enzymes can reactivate both estrone and estradiol from their packaged forms (Ervin 2019). The idea is that the makeup of your gut bacteria could nudge how much estrogen you reabsorb (Baker 2017).

What does the research actually show?

In a study of 51 NIH volunteers, urinary estrogen levels in men and postmenopausal women correlated strongly with gut microbiome richness and diversity. In premenopausal women, whose estrogen swings across the cycle, there was no relationship (Flores 2012). In 60 postmenopausal women, a more diverse microbiome was linked to a higher ratio of estrogen metabolites to parent estrogens, a pattern researchers have connected with lower breast cancer risk (Fuhrman 2014).

The evidence is early, though. In a mouse model of breast cancer, a drug that blocked one class of estrogen-reactivating gut enzymes did not reduce tumor development (Ervin 2019), a reminder that the system is more complex than one enzyme. Reviews describe a possible link between the estrobolome and estrogen receptor-positive breast cancer after menopause as a hypothesis that needs testing in larger prospective studies (Kwa 2016).

Does the estrobolome matter in menopause?

After menopause the ovaries make very little estrogen, and the remaining estrogen comes mostly from fat tissue. Gut recycling may modestly influence those lower levels. Researchers are exploring links between the gut microbiome and postmenopausal bone health, weight and metabolic health, and vaginal health, but none of these has led to a proven treatment (Baker 2017).

What's clear is that no change in gut bacteria can replace the estrogen the ovaries stop making. If hot flashes, night sweats, sleep problems or vaginal dryness are your main concerns, the treatments with the strongest evidence act on estrogen directly or on the brain's temperature control. More on the gut side of midlife in menopause gut health.

How might the estrobolome change through life?

• Reproductive years. The ovaries produce so much estrogen that gut recycling is a small part of the total; in the NIH study, premenopausal women's estrogen levels showed no relationship with gut bacteria (Flores 2012).
• Perimenopause. Ovarian output swings widely, and those swings likely dwarf any gut effect. Diet and gut health still matter for bloating, bowel habits and weight.
• After menopause. With ovarian estrogen low, the share influenced by fat tissue, liver and gut processing is larger, which is why most estrobolome research focuses on postmenopausal women.
• Two-way traffic. Estrogen itself appears to shape the gut microbiome and gut lining, so changes in hormones may alter gut bacteria as much as the other way around (Baker 2017).

Signs your estrobolome is "off": what to make of them

Online lists often attribute bloating, heavy periods, PMS, weight gain or breast tenderness to an imbalanced estrobolome. Those symptoms are real, but none can be traced to gut bacteria in an individual person with current tests. They have well-understood causes, from perimenopause and fibroids to irritable bowel syndrome and thyroid problems, that deserve proper evaluation. See estrogen dominance for how to think about those symptoms.

What may help a healthy gut-hormone balance?

These steps support a diverse microbiome and overall health. Their specific effect on estrogen is plausible but not proven.

• Eat more fiber and a wider variety of plants. Beans, lentils, whole grains, vegetables, fruit, nuts and seeds feed the bacteria that produce beneficial compounds. Ground flaxseed and cruciferous vegetables also affect estrogen metabolism directly; see the estrogen dominance diet.
• Add fermented foods. In a 10-week randomized study, a diet high in fermented foods (yogurt, kefir, kimchi, sauerkraut, kombucha) increased microbiome diversity and lowered markers of inflammation (Wastyk 2021).
• Limit alcohol, which raises estrogen levels and disrupts the gut lining.
• Use antibiotics only when needed. They reshape gut bacteria, sometimes for months.
• Move regularly and protect sleep, both linked to a healthier microbiome.

Probiotics and supplements

Probiotics are sometimes marketed as "estrogen-balancing." Strains differ widely, and there's little human evidence that any particular probiotic changes estrogen levels or menopause symptoms. Calcium-D-glucarate is marketed to block beta-glucuronidase, but human data are very limited. If you want to try a probiotic, choose one with third-party testing and treat it as an experiment; see probiotics for perimenopause.

Should you test your gut?

When to look beyond the gut

If menopause symptoms are affecting your sleep, work or relationships, talk with a licensed clinician about options that work directly. For hot flashes and night sweats, menopausal hormone therapy is the most effective treatment, with nonhormonal medicines as alternatives. Amie's clinicians can review your history and, if appropriate, prescribe Amie HRT+, a compounded estradiol and progesterone cream. It is not FDA-approved, and the clinician decides whether it's right for you.

The bottom line