Soy contains a certain kind of molecule called a “phytoestrogen” that acts like estrogen in the body.Health professionals disagree strongly about whether phytoestrogens are healthy for women to eat. Is soy (and flax, another potent phytoestrogen-containing food) the fountain of youth, or is it a toxin?

What is a phytoestrogen?

Phyto is Greek for “plant.” Estrogen means estrogen. Phytoestrogens are varieties of estrogen found in plants. Unfortunately, they do not exactly resemble the body’s natural estrogen. This makes the effect they have on health complicated.

There are several types of phytoestrogens.  The primary kinds are coumestans, isoflavones, and lignans.

Primary types of phytoestrogens

So what foods contain phytoestrogens?

Phytoestrogens can be found in many foods. This list documents the phytoestrogen content in some common foods. Some of the items are not surprising; Flax and Soy rank as number one and two respectfully. Some unexpected foods that contain phytoestrogens include garlic, hops and olive oil.

By far, the foods that contain the most phytoestrogens are soy and flax. These are so high in phytoestrogens that they can impact pretty much everybody, no matter their hormone health. Foods lower in phytoestrogen content such as chick peas or wheat have a very minimal phytoestrogenic impact. For most “healthy” people they shouldn’t be a problem. For women with hormone balance issues (such as me) , however, they may also still have an effect.

In all cases, with hormone balance issues, as well as people who regularly consume vegetable oils, nuts and soy, would do well to consider how potent their phytoestrogen intake may be.

What is estrogen?

Estrogen is actually a catch-all term for a wide variety of chemicals with similar shapes and functions, such as estrone (E1) and estradiol (E2). During a woman’s reproductive years, estradiol levels are much higher than other estrogens. During menopause, estradiol levels drop off, and the bulk of a woman’s estrogen content becomes E1 and E3 (estriol). This is important because E2 is the form of estrogen the ovaries pump out, and is also what is has the greatest effect in a woman’s reproductive years on partitioning fat to the hips and thighs rather than the abdomen. Plummeting E2 is why many women experience increases in abdominal fat during menopause.

E1- Estrone – Weak form of Estrogen, prominent throughout menopause

E2- Estradiol – Strongest and most prominent until menopause, active during reproductive years

E3- Estriol – weakest of the three, levels vary throughout the reproductive and menopausal course

How does the body perform estrogen signaling?

Estrogen is a hormone, which means that it is one of the chemicals in the body that works primarily as a signal: it tells cells and organs what they should be doing.  The sex hormone signaling process “begins” in the pituitary (with overhead influence from the hypothalamus in the brain).  It is up to the pituitary to tell the ovaries what to do, which is to produce estrogen.

The hypothalamus and pituitary glands have estrogen receptors liberally positioned through them.  These receptors tell them how much estrogen is circling throughout the body at any given time.

Think of it like keys and locks: estrogen receptors are the locks, and estrogen molecules are the keys.  With more keys, more locks can be filled. With fewer keys, locks end up sitting there empty, and rusted.

Phytoestrogen estrogen

When the locks are filled, the pituitary detects “estrogen sufficiency!” in the body, and it slows down the “please pump estrogen” signal it sends to the ovaries.  This makes the ovaries produce less estrogen.

The whole purpose of this system is to maintain stable estrogen levels in the blood.  

Unfortunately, consuming high quantities of phytoestrogens often interferes with this otherwise healthfully functioning feedback loop.

The medical community’s opinion on what this means

Phytoestrogens act as estrogen in the body.  But here’s the problem: while phytoestrogens have a pretty good ability to bind to estrogen receptors, they are not able to signal as well as estrogen.

Phytoestrogens look enough like estrogen to bind to estrogen receptors, but they do not look exactly like estrogen.  This makes their ability to perform estrogen functions inferior to true estrogen.

When you eat phytoestrogens, they enter your bloodstream. To many doctors, this means that women with low estrogen levels should eat phytoestrogens. In their perspective, phytoestrogens would signal “fullness” to the estrogen receptors. They would also perform the normal functions of estrogen in the body.

On the other end of the spectrum, many doctors argue that women with high estrogen levels should supplement with phytoestrogens.  This is because the phytoestrogens would flood the estrogen receptors. These receptors would down-regulate estrogen production. And, because these phytoestrogens do not resemble true estrogen, estrogenic activity would not actually increase. It would decrease. This, many doctors argue, could overall decrease estrogen production and possibly reduce risks of certain cancers.

In both of these cases, however, the science is not clear cut. Some doctors may think that women with both high and low estrogen levels should supplement with phytoestrogens, but that’s not always a great solution. For women with high estrogen, it can still sometimes make it worse. There simply could be far too much. For women with low estrogen, it can also make it worse. Since different kinds of phytoestrogens communicate differently with different kinds of estrogen receptors, depending on which phytoestrogen women with low estrogen levels consume, it could actually do more harm than good.

Something you may want to look into then is how to support healthy estrogen production first without using phytoestrogens.

How to balance estrogen levels

– Increase fat mass, if underweight

Decrease fat mass if overweight

– Exercise when it feels right

– Eat anti-inflammatory, paleo foods like organic vegetables and fruits, organ meats, here’s a supplement in case you do not like to eat liver), eggs, fermented foods (on this page are my favorites) and the rockstar superfood cod liver oil can go a long way.

– Sleep.

– You can read about all of these and additional suggestions in my book, available here.

But what about the other types of Phytoestrogens?

There are three primary types of phytoestrogens (plus dozens of sub-types): lignans, coumestans, and isoflavones. There are two types of estrogen receptors: estrogen receptor alpha (ERa) and estrogen receptor beta (ERb).

Different estrogen receptors have different shapes, and are distributed unevenly throughout the body.

ERa is concentrated more heavily in the hypothalamus than ERb, for example.

ERb is concentrated more heavily in skin tissue. It also varies for fat cells, for ovarian cells, for different types of brain cells.

Edit 2017: Recently, after learning about new research and working with even more women, I’m finding that plant-based phytoestrogens may promote ER beta activity, which can lower estrogenic potency in the body as a whole, thereby decreasing the risk for certain cancers (this is not true of synthetic estrogen, like that in hormonal birth control or estrogen replacement therapy). Read more about these latest studies right here

Coumestans have a unique chemical shape (with two hydroxy groups in the same position as estradiol).   Coumestol has the same binding affinity for the ERb receptor as estrogen, but it has much less of an affinity for ERa.  This means that ERb’s will get filled up by coumestans, but ERa-heavy tissue might suffer a decrease in estrogen-like activity because estrogen production in general gets down-regulated by the hypothalamus, pituitary, and ovaries, etc.., thus making estrogen levels decrease in ERa tissues relative to ERb.

Additionally, the shape of coumestans means that coumestans have the ability to inhibit aromatase.

Aromatase is the process of converting testosterone to estrogen in cells.  This can be helpful to know for women with PCOS who have high testosterone and low estrogen levels: it may be helpful to avoid coumestans.

Different isoflavones bind to different estrogen receptors differently. Some bind more strongly to ERa, and others to ERb (genistein, dihydrogenistein to ERb, equal to ERa).  Yet most importantly, many (though not all) isoflavanones that have been tested have the same binding affinity as actual estrogen, but half the receptor-dependent transcriptional power. This is a powerful fact: isoflavones have half of the ability to perform estrogenic function as they do to take up space. Isoflavones such as soy can help women with estrogen dominance.

The takeaway

Phytoestrogen biochemistry is complicated. Some studies have shown that phytoestrogens boost estrogen activity, and others have shown that they decrease estrogen activity. This is due in part to the variable biochemical components of different kinds of phytoestrogens I listed above. It may also be due to the broad diversity of women’s physiological responses to phytoestrogen.  What were the women’s estrogen levels beforehand?  Were they healthy women?  Fertile women? Women on the pill or grew up eating soy?  Those who are routinely exposed to xenoestrogens?  There are too many questions and the variables are still too numerous to say whether all women should avoid soy.

Something we can say definitively however is that women should tread carefully around soy, flax, and other phytoestrogens.

I am a firm believer in bioindividuality. Some women could benefit from phytoestrogen usage. Some may not. It is up to you to figure out which you may be. If you are extremely low or extremely high in estrogen, it seems likely that phytoestrogens could help.

If you do not know, step carefully. It is better to be safe than to be sorry. You can work on balancing your hormones first and foremost through adequate carb and fat intake, through smart exercise (for a way to achieve this at home, click here), through stress reduction, and through an anti-inflammatory diet rich in nutrients.

If you want to experiment with phytoestrogens, start small. Perhaps with a daily bowl of chickpeas or hummus. This is what I personally do.

For further resources on phytoestrogens and how they interface with health :

Why I now believe Phytoestrogens may be good for you

Phytoestrogen Sources you Might not Know You’re Consuming

Menopause and Hot Flashes

Losing weight while you get older 

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