estrogen dominance

What do you get when you cross estrogen with your microbiome?

Content reviewed by Donna Gates
Written by Body Ecology on March 20th, 2021

You’ve certainly heard of the microbiome by now: the trillions of bacteria, viruses, phages, yeast, archaea, and parasites that are living in your digestive tract — mostly the colon. But what do you get when you combine the word “microbiome” with the hormone, estrogen? As you might guess, it’s the “estrobolome.”


Can sipping a potent probiotic positively impact your estrobolome? Several studies say: It’s likely.18

Disruption of the estrobolome may also be linked to polycystic ovary syndrome.

The estrobolome is the estrogen microbiome. It’s the bacteria in the gut whose genes play a key role in the metabolism or breakdown of estrogen. The estrobolome significantly influences the amount of estrogen circulating throughout your body. When your estrobolome is not functioning properly, you become estrogen dominant — not good if you’re a woman, and this is true for men too.

Over recent years, researchers have begun investigating the links between this estrobolome and the risk of disorders caused by chaotic estrogen metabolism, such as some forms of breast, ovarian, and prostate cancer.

What they’ve found could lead to significant changes in how we think about cancer detection and prevention and hormonal balance.

Estrogen 101 made simple: Your body produces 3 types of estrogen

At a basic level, estrogens are steroid hormones made from cholesterol. The main forms in the human body are:

  • Estrone (E1) – The most common kind in females after menopause.
  • Estradiol (E2) – The most common kind in nonpregnant females prior to menopause.
  • Estriol (E3) – The kind that’s highest during pregnancy.

These estrogens (and others) circulate in the blood in free form or bound to proteins. They interact with tissues and exert a wide variety of biological effects — including promoting the development of secondary sexual characteristics, such as breast growth. They also affect bone density, cardiovascular health, libido, skin health, and brain and mental health.

Estrone is a weaker form of estrogen that the body can convert into other types of estrogen as needed. Estriol rises in pregnancy to help the uterus grow and to prepare the body for delivery. It peaks just before birth, and levels fall in the following months until estradiol becomes the dominant form again.

Both men and women produce estradiol (E2):

  • In males, E2 (estradiol) is essential for the maturation of sperm and for maintaining libido.
  • In females, too little E2 ties to weight gain and cardiovascular disease.1 Too much E2 in females may contribute to acne, osteoporosis, depression, and loss of libido, with very high levels linked to a greater risk of uterine and breast cancers.2

Understanding what these different types of estrogen do is important because it can help you to understand what could happen if your estrobolome becomes unbalanced.

To learn about another potential cause of disrupted hormones, candida, download our Candida Report. It’s free.

So, tell me more about my estrobolome…

Estrogens are produced primarily in the ovaries, adrenal glands, and adipose (fat) tissue. As they circulate around the body, they’re acting as hormonal messengers, telling cells and tissues what to do. While they deliver these messages, they’re often broken down and reshaped into estrogen “metabolites,” which are no longer active in the same way. These new types of estrogen metabolites have widely varying potencies and half-lives (how long they linger around in the body).

Estrogen can only stay for a certain time in the body and then moves to the liver for further processing and excretion. In the liver, the estrogen metabolites are combined with other substances — one process is called “glucuronidation”— and the estrogens now become water-soluble. The liver then makes bile and puts the water-soluble estrogens into the bile so they can be eliminated from the body — mainly in the stool. Some estrogens are sent directly to the kidney and are eliminated in the urine.

And here’s where the estrobolome comes in:

  • Once estrogens reach the colon where they combine (conjugate) with bile, some of the bacteria making up the estrobolome act upon them.
  • Some unfriendly bacteria, such as E. coli HGU-3, have genes that produce an enzyme called beta-glucuronidase.
  • Beta-glucuronidase changes the estrogen metabolites back into an active (deconjugated) form that can be reabsorbed back into circulation, basically reversing the normal process of detoxification and resulting in more reabsorption of free estrogens.
  • High levels of beta-glucuronidase can be measured in the stool and may increase your risk for breast, prostate, and colon cancer.3 Milk thistle has been found to help inhibit beta-glucuronidase.4

This may create estrogen dominance and could, over time, increase the risk of estrogen-driven cancers.5

When the ecology of the intestines is out of balance — or dysbiotic — the more beta-glucuronidase is produced by unfriendly bacteria. The more beta-glucuronidase is produced, the more estrogen is reabsorbed back into the liver, and the less estrogen is eliminated via the stool. Too much estrogen is called “estrogen dominance.” As the estrogen is reabsorbed into the liver, the more it is recirculated, potentially increasing risk of breast, ovarian, endometrium, and prostate cancer.5

The estrogens that reabsorb are typically different from the original estrogens. Either way, these estrogens once again exert their effects on target tissues. This might mean stimulating cell growth in breast tissue or elsewhere in the body, potentially contributing to prostate growth, endometriosis, or polycystic ovary syndrome.6

Hopefully, you’re now beginning to see how the makeup of the bacteria in the estrobolome play a role in a woman’s (or a man’s) lifetime exposure to estrogen — and how the presence of unfriendly microbes can affect your risk for cancers that are driven by estrogen not being properly eliminated. If your estrobolome has too many unfriendly bacteria, they rapidly alter the levels of estrogens being eliminated and influence how much estrogen reenters circulation.

What happens when your colon is out of balance?

The wrong bacteria producing high levels of beta-glucuronidase disrupt your ability to detoxify the estrogens made by your body, as well as estrogen-producing environmental chemicals. Don’t forget: You could be obtaining estrogen in milk and meat too. Any excess estrogen is “estrogen dominance.”

Even in postmenopausal females, a variety of health concerns are associated with estrogen dominance and estrobolome disruption besides cancer.

These include a greater risk for:

  • Cardiovascular disease
  • Obesity
  • Osteoporosis

Highlighting the likely impact of the estrobolome, researchers have found a high prevalence of gut dysbiosis in individuals who are obese or who have cardiovascular disease or osteoporosis.7-9 It even seems that people with type 2 diabetes and atherosclerosis have their own recognizable microbiome signature.8

Disruption of the estrobolome may also be linked to polycystic ovary syndrome (PCOS), characterized by excess testosterone relative to estrogen.10


  • These effects of the estrobolome on testosterone and estrogens can even have an impact on prostate health.
  • Although research is lacking currently, there seems to be a link between gut dysbiosis and prostate cancer.11
  • Interestingly, higher levels of estrogen (perhaps because of a disrupted estrobolome) have been suggested as a contributing factor in the development of prostate cancer.12

Finally, gut dysbiosis has also been linked to abnormal tissue growth in estrogen-sensitive tissues, such as the breast and endometrium.10,13

At least 6 factors that might be affecting your estrobolome

When the microbiome is balanced and healthy, the estrobolome deconjugates enough estrogen to maintain a good balance in the body. But, just as the microbiome in general is affected by antibiotics, diet, drugs, stress, and other factors, so too is the estrobolome. And when estrobolome balance is off, beta-glucuronidase activity can be too high or too low, leading to an excess of free estrogen in the body or a deficiency of hormones.

These are just some of the outside influences on your estrobolome:

1. Antibiotics. In one study, researchers found that increased use of antibiotics was associated with a higher risk of breast cancer in women and suggested that this may be connected to the effects of antibiotics on the estrobolome.14

2. Birth control and BPA. Hormonal contraceptives can also affect the estrobolome and circulating levels of estrogens, as can exposure to bisphenol-A (BPA), a chemical often found in plastics, the lining of food cans, and cosmetic and toiletry products.15

3. Food. Some foods might affect the estrobolome. These phytoestrogenic foods can have estrogenic or antiestrogenic effects, meaning they may either protect from or promote certain estrogen-dependent diseases.16 And it seems that the estrobolome may be the major player in determining what effects these phytoestrogens have on a person’s levels of circulating estrogen.

4. A high-fat diet. Research shows that people who eat a higher amount of saturated fat have higher beta-glucuronidase enzyme activity in the gut.17

5. Obesity. This may also affect the estrobolome since fat cells produce estrogen.

6. Gut-brain axis. There may be as yet undocumented links between the estrobolome/gut-brain axis, with implications for mental/emotional wellbeing tied to hormone recirculation. Interestingly, just as the gut-brain axis is bidirectional, with the brain able to influence the gut microbiome in some ways, so too might the hormonal system influence the estrobolome. In pregnancy, for example, changes in blood glucose regulation may cause changes in mucosal secretions that affect the growth of bacteria. This is partly why genitourinary tract infections are more common in pregnancy.

A handful of studies in non-human animals suggest that supplemental probiotics, both multi-strain and specific strains, can have benefits for the estrobolome. In one animal model of PCOS, a broad-spectrum Lactobacillus probiotic helped lower testosterone production and normalize the estrous cycle.18 In menopausal mice, L. reuteri was seen to prevent bone loss linked to low estrogen, while another animal study found that L. gasseri lessened the growth of endometrial tissue outside the uterus.19,20

It also appears that:

  • The Standard American Diet (SAD) favors the dominance of bacteria that produce high levels of beta-glucuronidase.
  • This means that a greater amount of estrogen is returned to circulation, which, as mentioned, may raise the risk of estrogenic cancers and other conditions.21
  • This kind of diet also reduces the production of short-chain fatty acids that are essential for a healthy gut lining. The SAD diet helps increase levels of inflammation and insulin resistance.

The better option, by far, is a whole-food, plant-based diet that is high in fiber and the right probiotic foods. This supports a healthy and diverse microbiome and, by extension, estrobolome. A diet that reduces animal proteins and is rich in vegetables helps the body to better manage levels of deconjugation to keep recirculating estrogen levels in check.

Broccoli sprouts and cruciferous vegetables are very important to add to your diet. Since fermented vegetables can be made with cruciferous vegetables, like red and green cabbage, daikon, and kale, please include these invaluable foods too. Fermented vegetables contain live organisms, which promote a healthy population of friendly bacteria in the gut to maintain beta-glucuronidase balance.

A diet like Body Ecology recommends also supports the production of short-chain fatty acids (SCFAs) in the gut, helping to uphold a functional intestinal barrier to prevent molecules and potentially carcinogenic chemicals from getting into circulation.

Although research into the estrobolome is still just beginning, there are plenty of good reasons to take steps to support a healthy diversity of gut microbes that include estrogen-metabolizing bacteria. In practice, this means making sure to eat prebiotic and probiotic foods that provide both the bacteria themselves and the indigestible fiber beneficial bacteria like to eat.


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