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The Role of Gut Bacteria in Fertility and Estrogen Dominance

I’ve talked before about the importance of optimizing your gut health before getting pregnant in order to promote a healthy pregnancy for both you and your baby.

But what about getting pregnant in the first place… Can your gut bacteria play a role in your hormone balance and fertility?

The science suggests that it very well might!

To understand why let’s take a closer look at infertility and one of its common causes: estrogen imbalance.

INFERTILITY & ESTROGEN DOMINANCE

When you hear the term “infertility,” you likely think of a person or a couple that cannot and will never be able to have children. In the medical world, however, infertility does not refer to a permanent state at all.

A diagnosis of infertility simply means that you have not been able to get pregnant after a year of normal, unprotected sex (1).

It’s actually a diagnosis that is far more common than you might realize. According to recent statistics, between 7% and 15.5% of American women experience infertility in any given year, and the majority of women (51.8%) meet the criteria for infertility at least once during their menstruating years (2).

While there are many reasons a couple might have difficulty getting pregnant, among the most common are hormone imbalances (3, 4). And abnormally high levels of one specific sex hormone is frequently implicated in infertility in both men and women: estrogen (5, 6, 7, 8).

Let’s look at each of these individually.

ELEVATED ESTROGEN AND FEMALE INFERTILITY

Most women need little reminder that our fertility depends on a highly-coordinated 28ish-day cycle in our hormone levels. Most of us also know that one of the key players in this hormonal dance is estrogen.

Estrogen has two very important jobs in the female menstrual cycle. First, it triggers a spike in the levels of a hormone called luteinizing hormone (LH) from the pituitary gland in the brain. This spike in LH levels is what triggers the ovary to release a mature egg into the fallopian tube, where it can be fertilized (9).

After a successful ovulation, though, estrogen works together with yet another hormone called progesterone to prevent a second ovulation from occurring. Estrogen and progesterone do this by acting on the pituitary gland in the brain to make sure no more LH is made until the following cycle (or, if pregnancy occurred, until after birth). At the beginning of the next cycle (menstruation), estrogen and progesterone levels dip down, signaling to the brain that it is safe to produce another spike of LH (9).  

Constant high levels of estrogen, without a significant dip signaling the start of a new cycle, can trick your brain into thinking you’ve already ovulated, and prevent you from ovulating again (9). This is actually the logic behind hormonal birth control (the pill).

As you might imagine, this can play a significant role in infertility.

ELEVATED ESTROGEN AND MALE INFERTILITY

While we often think of estrogen as a female hormone, men also have healthy baseline levels of estrogen that are required for sexual and reproductive functions.

At moderate levels, estrogen promotes (and is necessary for) a healthy libido and the production of sperm in men. At elevated levels, however, estrogen can have the opposite effects (6).

Too much estrogen in men decreases their libido. This is because, as in women, estrogen in men acts on the pituitary gland in the brain to decrease the production of LH. In men, this hormone stimulates the testes to produce testosterone. Without enough LH, there is a drop in testosterone, and low testosterone lowers male libido (6).

Elevated levels of estrogen also decrease the production of sperm by the testes. This is due to the estrogen-induced decrease in LH and testosterone levels, both of which directly stimulate the testes to produce mature sperm (6).

ESTROGEN & YOUR GUT BACTERIA

Clearly, a buildup of estrogen is not optimal for you, or your partner’s, fertility. But what’s any of this have to do with your gut bacteria?

A lot, believe it or not! There are multiple mechanisms which link your gut bacteria to your estrogen levels.

GUT BACTERIA AND ESTROGEN REABSORPTION

Your gut bacteria are actually an integral part of the normal regulation mechanisms your body uses to keep estrogen levels normal.   

See, every day your liver pulls estrogen out of your blood and binds it to a sugar-metabolite called glucuronic acid. This sugar-estrogen complex is then mixed with your bile, which is dumped into your digestive tract to help with digestion (10, 11, 12).

Now, this sugar-estrogen complex is bigger than estrogen by itself and it can’t be absorbed through the intestinal wall very well. Because of this, much of the estrogen gets stuck in the intestines and is eliminated from your body via bowel movements (10, 11, 12).

And this is where your gut bacteria come in. They have special enzymes that are able to cut estrogen free from the sugar, called β-glucuronidases. The freed estrogen molecule can then be easily absorbed and re-enter your bloodstream (10, 11, 12).

This is a natural part of the process and the liver binds more estrogen to bile acids than needed with the knowledge that some of it will be coming back, thanks to your gut bacteria.

This balance can be upset, however, if you have abnormal numbers, types or ratios of bacteria in your intestines (called dysbiosis) (13).

This is because some gut bacteria have β-glucuronidases that free estrogen better than others (14). With an unhealthy mix of gut bacteria, your microbiota can free too much estrogen, allowing much greater levels of estrogen to be reabsorbed back into your body than normal and pushing estrogen levels in your blood up (13).

GUT BACTERIA AND ESTROGEN FROM FOOD

In addition to the role the gut microbiota play in balancing the levels of estrogen you make yourself (called endogenous estrogen), they also regulate how much estrogen and estrogen metabolites you absorb from food sources (called exogenous estrogen).

Some gut microbes have enzymes that enable them to breakdown phytoestrogens (from plants) and polycyclic aromatic hydrocarbons (from barbequed or fried meats) into estrogens (15, 16). These estrogens can then be absorbed through the intestinal wall, raising your blood levels.

In fact, studies show that in men and postmenopausal women, the number one source of estrogen for their whole bodies is intestinal absorption from their food (17). And dysbiosis is associated with higher levels of estrogen in these populations, presumably at least partially through increasing the breakdown of dietary molecules such as phytoestrogens and polycyclic aromatic hydrocarbons (13).

INDIRECT WAYS GUT BACTERIA AFFECT ESTROGEN LEVELS

In addition to the direct ways dysbiosis links your gut health to higher estrogen levels, there are also several indirect links.

For example, an abnormal balance of gut bacteria has been strongly linked to constipation (18, 19), inflammation (20) and obesity (21), all of which may be able to further drive up estrogen levels in your blood (8, 22, 23).

IMPROVING YOUR ESTROGEN BALANCE WITH BETTER GUT HEALTH

So, what does this mean for you if you are planning to get pregnant? What can you do to optimize your estrogen levels and boost your fertility?

Research shows that one of the most beneficial things you can do to optimize your estrogen levels is increase your fiber intake.

A high fiber diet is associated with improved microbial health and decreased risk of dysbiosis (24). In fact, increasing the amount of fiber in your diet for just 2 weeks is enough to significantly improve the composition of your gut bacteria (25).  

Additionally, fiber may be able to directly bind the estrogen-sugar complex in the digestive tract, helping eliminate it from the body. In a study examining estrogen (re)absorption in women, there was a direct and significant relationship between a woman’s fiber intake, the size of her stool, and the amount of estrogen she was able to flush from her body (26).

How you choose to increase your fiber intake is up to you, but boosting your fiber intake by increasing the amount of fiber-rich foods in your diet, rather than through adding fiber supplements, may give you more bang for your buck.

This is because the dietary source of fiber — plants — are also rich in polyphenols (27, 28, 29). As I outline here, polyphenols can help boost the health of your gut bacteria, so plant-based fiber-rich foods treat your dysbiosis to a one-two punch.

While fiber (and fiber-polyphenol-rich plants) is the most well established dietary tool to prevent dysbiosis and lower blood estrogen levels, other dietary and lifestyle changes may also be helpful. These include:

  • Exercising regularly (30)
  • Drinking enough water to stay properly hydrated, preventing constipation (31)
  • Taking a probiotic, which contains healthy gut bacteria that can help repopulate your gut with healthy microbes (32)
  • Avoiding broiled, fried and barbequed meats that are likely to contain high levels of polycyclic hydrocarbons (33)

However, if you have a lot of digestive symptoms like constipation, diarrhea, bloating, or gas, you may need help beyond these simple dietary and lifestyle changes.

This is because digestive symptoms can indicate that you have severe dysbiosis, or conditions like SIBO or parasites that need a more in-depth approach, including antimicrobials (or antibiotics) and other supplements.

That said, you can have imbalanced gut bacteria without any symptoms at all, so if you want to maximize your chances of getting pregnant or prevent estrogen dominance, it’s a good idea to test even if you don’t have digestive symptoms.

There are multiple tests to determine the health of your gut microbiota that can give you more precise information regarding your gut health. This can provide you with a roadmap to optimizing your digestive health and, in turn, your fertility.

If testing indicates you have dysbiosis, SIBO, or any other type of imbalanced gut flora, you’ll want to clear out that bad bacteria and balance your biome. If you need more help with that, check out my 8-week online program, Build Your Biome.

For women who have ever struggled with infertility, did you experience that taking care of your gut health through diet and lifestyle changes made a difference in your ability to get pregnant?

For women who are thinking about starting a family in the near future, do you think you will consider your gut health more now, before you start trying? Tell me in the comments below!

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