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The Soy Slander

Miranda has a Master's in Human Nutrition from Christian-Albrechts-Universität and a passion for promoting accurate nutrition information.


I expected a lot of resistance and social struggles when I went plant-based. I knew the protein thing was coming. And probably concerns and questions about my bones. And if I’m hungry all the time.

But one thing I was not expecting, at all, was people’s reactions to me eating soy. It turns out that people get really, really weird when you eat soy in front of them.

Some people respond with awe. (“You’re so healthy! I wish I could eat like you!”)

Others, with awed-horror. (“Wow! You’re going to eat tofu? I could never do that! It’s just so weird!”)

Yet others are inexplicably embarrassed or feel judged. (“I know, I know, I should order that, too. But I just need some meat today, okay?”)

Once in a great while, someone seems to think I’ve signed some sort of vegan-club-contract that requires soy consumption on a regular basis, like some sort of plant-based communion ritual. (“Did you know you were going to have to eat tofu when you went vegan?”)

But in most cases, people respond with some variation of, “Isn’t soy full of dangerous, cancer-causing, sperm-killing estrogens?”

Soy Sidenote

Now, before we go any further, let me say I’m not a full-throated supporter of soy, by any means. I think there are a lot of totally legit reasons not to eat soy.

Not a fan of monoculture soy fields destroying ecosystems and don’t want to promote industrialized soy farming with your hard-earned money? Totally get it.

Don’t trust Monsanto’s claims that the super-potent herbicide used on their GMO soy is safe and don’t trust you’re getting your hands on GMO-free soy? With you 100%.

Find the fact that an enormous percentage of soybeans produced go to feed livestock to make meat for the industrialized world, rather than to feed the hungry, morally uncomfortable and don’t want to support the industry? Got it!

On a whole-foods diet and not cool with how processed many soy foods are? Again, 100% on your side.

Just really don’t like the taste? Absolutely legit!

Allergic? Seriously, seriously don’t eat it!

But you don’t need to avoid soy for the “estrogen”.

The Soy Slander

The idea that soy is dangerous because of its “estrogens” took root in the 1990s. In fact, I can remember the wave of anti-soy news stories, magazine articles and everyday chit-chat that swept the culture at the turn of the millennium.

Like a tsunami created by an earthquake, this anti-soy wave was triggered by scientific studies that had made (at the time, genuinely) a worrisome discovery.

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Soy is very, very rich in phytoestrogens.

Phytoestrogens and Soy

Just like estrogens are hormones in humans, phytoestrogens are hormones in plants. (Yeah! Plants have hormones! Nifty, huh?)

The plants use these hormones to help regulate their growth, leaf development and pollen production, to coordinate their responses to sunlight and to get rid of toxins. They’re seriously important to plant biology and all plants have them!

So any time you munch away on a plant food, you’re getting some phytoestrogens -- and scientists knew that. But these hormones were in such tiny concentrations in most plants and plant-foods that no one paid much mind.

Until soy was tested. And they were absolutely chock-full of phytoestrogens.

You weren’t just getting a couple of molecules of phytoestrogens when you ate soy. You were getting a lot. Like, enough to be able to have a legit, detectable concentration of them in your blood and urine.

And this made researchers a little worried.

Phytoestrogens and Health Concerns

See, estrogens and phytoestrogens aren’t just similar in name. They are also very, very similar in shape and structure. And the way estrogen works in your body is 100% dependent on its shape and structure.

Estrogen works by sending signals through super-specialized receptor molecules. The receptors (aptly named the “estrogen receptors”) are tailor made to fit estrogen, and estrogen only, so that estrogen signals are only sent when estrogen is around.

But, since phytoestrogens are so close in shape and size to human estrogens, researchers were concerned they might be able to stick to the estrogen receptors and trick your body into thinking you had actual estrogen around.

So, they tested it. And sure enough, soy phytoestrogens could stick to human estrogen receptors.

Now, scientists were pretty worried. If phytoestrogens could bind estrogen receptors, they could potentially send all the signals estrogen can. And since the soy phytoestrogens weren’t “natural” -- weren’t made because your body needed estrogen -- they would, by definition, be creating a kind of overdose. Not a poisonous overdose -- just an unnatural, too high dose.

What do unnaturally high doses of estrogen do in humans? That we already knew from disastrous birth control attempts, hormone replacement therapies, and the changes in hormones caused by alcoholism:

  • In women: promote breast, uterine and ovarian cancer
  • In men: cause infertility, loss of libido and the development of breasts

So, researchers put out statements, warning about potential risks of soy phytoestrogens.

How could they not tell the public? This was something that could, potentially, have some serious health consequences. Everyone had a right to know there was a potential risk.

But, then, when they moved from the petri dish to people, everything changed.


Putting the Slander Asunder

The first sign that the petri dish experiments weren’t telling the whole story came from population studies like this.

Researchers asked groups of women about their diets and ranked them according to how much soy they ate. Then, they looked to see which of the groups had the highest rates of breast cancer (one of the cancers that, potentially, could be driven by phytoestrogens).

Rather than the highest rate being in the group that ate the most soy, the way the scientists predicted, it was in the group that ate the least.

The more soy women ate, the lower their risk of breast cancer.

And they didn’t find this relationship in just a single study. It’s been found dozens and dozens of times.

The story is similar with soy and male health and fertility.

When researchers looked at the reproductive health of men consuming lots of soy they saw… nothing. No change in testosterone levels. No change in sperm count, motility or health.

Now, population studies are tricky things. You can’t say for sure that soy is the single factor protecting women’s breasts, or that soy has no effect on men’s reproductive health from studies like this. (Maybe women who eat soy also exercise a lot, and that’s what’s preventing the cancer. Maybe the soy is damaging men’s sperm production, but men who eat soy also smoke less, and that balances things back out.)

But, the fact that the expected negative effects from soy weren’t there or were turned all the way into positives -- raised some eyebrows. Clearly, the soy story was more complex than originally thought.

At minimum, the effects of soy phytoestrogens were weak enough that other factors could overpower them. But, potentially, the effects were actually healthy!

So, the second round of studies was off to figure out which of these was the case.

And the answer came from a closer examination of the estrogen receptors!

Estrogen Receptors: The Good, The Bad and The Un-Soy-y

Right around the time all the soy stories were coming out, a researcher named Sieste Mosselman and his team dropped a bombshell on everyone studying estrogen.

There isn’t one type of estrogen receptor. There are two!

The original receptor, now called “estrogen receptor alpha” (or ERa), dominated in the breasts and ovaries. It was responsible for promoting breast cancer, the reproductive cycle in women.

The new receptor, christened “estrogen receptor beta” (ERb), dominated in bones, testicles and areas of the brain in charge of reducing stress. It was responsible for keeping bones dense, sperm production humming along normally, and preventing stress and depression.

With this new information, researchers tested the soy phytoestrogens on both receptors, not just ERa.

Guess what they found?

The phytoestrogens preferred to bind to ERb. A lot.


That, alone, should have been enough to basically clear soy’s name around breast cancer and male infertility. But, it turned out there was more!

More detailed studies found that when a soy phytoestrogen did decide to bind to an ERa receptor, depending on the exact type of phytoestrogen, it often didn’t actually activate it at all, or didn’t activate it nearly as much as actual estrogen.

So while phytoestrogens could activate ERa, when they were mixed in with normal estrogen (as is the case in an actual person), the net result is that estrogen-responses in cells are decreased! (Makes sense, right? Whenever a phytoestrogen is bound, an actual estrogen can’t be, so you have, on the whole, fewer activating signals.)

The Seriousness of the Slander

At this point, I think you can see both the unfairness and the irony of the reputation soy was given in the 1990s.

Not only do soy phytoestrogens not cause cancer or infertility, they actually help keep normal estrogen from causing those exact conditions by blocking ERa signalling.

People avoiding soy products to try to protect their reproductive health may be doing the exact opposite!

(Not to mention, they’re totally missing out on some of the extra health benefits of ERb activation, such as sturdier bones and improved mood -- which we’ll get into in more detail in another post someday!)

Now, as I said in the introduction, I don’t think you have to eat soy. It is not the only food on the planet that offers health-boosting phytoestrogens (all plants have some form of them, remember!) So, if you don’t like soy, for whatever other reason, don’t eat it!

But if your decision to skip soy stems solely from stress about your sexual health and the effects of soy phytoestrogens on your health, you can stop sweating it and tuck into that tofu!

Now, it’s your turn!

Do you eat soy? What motivated your decision? Might you reconsider your stance on soy now that you’ve learned more about soy and your hormones?

Let me know in the comments below! I’d love to hear your take on the soy debate!

Sources and Further Reading

Altieri, M. The Ecological Impacts of Large-Scale Agrofuel Monoculture Production Systems in the Americas.

Cassidy, E. Redefining agricultural yields: from tonnes to people nourished per hectare.

Davis, P. The Plant Hormones: Their Nature, Occurrence, and Functions.

Reinli, K. and Block, G. Phytoestrogen content of foods-a compendium of literature values.

Arai, I. et al. Comparison of isoflavones among dietary intake, plasma concentration and urinary excretion for accurate estimation of phytoestrogen intake.

Vrtacnik, P. et al. The many faces of estrogen signaling.

Weiss, N. and Sayvetz, T. Incidence of Endometrial Cancer in Relation to the Use of Oral Contraceptives.

Morch, L. et al. Hormone Therapy and Ovarian Cancer.

Muthusami, K., Phil, M. and Chinnaswamy, P. Effect of chronic alcoholism on male fertility hormones and semen quality.

Wu, A. et al. Tofu and Risk of Breast Cancer in Asian-Americans.

Wu, A. et al. Epidemiology of soy exposures and breast cancer risk.

Allen, E. et al. Soy Milk Intake in Relation to Serum Sex Hormone Levels in British Men.

Chavarro, J. Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic.

Mosselman, S., Polman, J. and Dijkema, R. ER-beta: identification and characterization of a novel human estrogen receptor.

Younes, M. and Honma, N. Estrogen receptor beta.

Mueller, S. et al. Phytoestrogens and Their Human Metabolites Show Distinct Agonistic and Antagonistic Properties on Estrogen Receptor α (ERα) and ERβ in Human Cells.

Kuiper, G. Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor beta.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2018 Miranda Poenicke


Miranda Poenicke (author) from Germany on September 10, 2018:

Thank you so much for your kind commen, Cecil! It is amazing that soy got such a bad rap with some of the healthiest cultures in the world were the ones eating it in spades!

Cecil Kenmill from Osaka, Japan on September 09, 2018:

Well-researched and well-presented. I live in Japan and the locals love their soy. Somehow they keep on ticking.

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