Soy and Cancer: What's the Connection?

Posted by Tyler J. Arsenault B.Sc (Nutrition) on 2017 Nov 10th

I’ve been steeped in the natural health industry for well over a decade; nearly two decades actually. During this time, the prevailing wisdom(superstition perhaps) among industry folk and consumers was that soybeans were a nasty thing; full of estrogens that led to a myriad of cancers. This feeling wasn’t unanimous among people by any means, but 20 years later I’m still hearing the odd person tell me how many feet the pole must measure before they’re willing to poke a soybean.

As a person who unequivocally lives and breathes science more than the average joe; perhaps at the risk of being socially stunted, I was curious if this “wisdom” had more in common with applying sunscreen when venturing out into the sun, or with knocking on wood after tempting fate.

So what’s all the hubbub about? Well soybeans contain natural chemicals called phytoestrogens, which is an umbrella term for any molecule that has a similar shape to estrogens. The basic knowledge of this fact (which is true), causes minds to start turning in a variety of ways leading to statements such as these (I’ve heard all of these):

“If soy beans contain plant estrogen, they’ll make men grow breasts like when men get a sex change and take hormone pills”

“If HRT (hormone replacement therapy) causes cancer, so would soy estrogens”

“Soy estrogens cause a decrease in testosterone, sperm count, and sex drive in men. Don’t even think about eating soy if you want to get your wife pregnant and remain manly”

“Soybeans make me rage harder when I have PMS, they’re the last thing I need”

I can understand how any rational person would make a causal or even correlative link between naturally occurring plant-based phytoestrogens and the concerns stated above. But are they founded in science? If I had a nickel for every incorrectly speculative connection of two variables based upon guesswork I’d be retired already.

Soybeans by OMG Lauren licensed under CC BY 2.0

First, let’s look at phytoestrogens as they seem to be the heart of the matter. Soy beans do in fact contain phytoestrogens, and these molecules are in fact similar to estrogen. But if we’re going to lay some hate on soybeans, why don’t we examine things more carefully. Are there other foods that have phytoestrogens? And do they have more, less or roughly the same concentrations as soy?

Flax seeds, are a seed that everyone loves. We tell our neighbours how we grind up flax and put it on our cereal, we tell our relatives that we’ve switched to whole grain flax bread, and we share how we’ve discovered a fantastic vegan alternative to fish oil omega 3s by taking a tablespoon of flax oil everyday. Flax is “the bomb”. Well it might pain you to hear that flax actually contains more phytoestrogen than soybeans. Actually nuts (in general) and oilseeds commonly have more phytoestrogens than soy too. Let’s look at a small example of other foods that contain phytoestrogens:

  • Flax
  • Coffee
  • Oats
  • Beer (hops)
  • Barley
  • Beans
  • Lentils
  • Rice
  • Apples
  • Carrots

Now, all I’m saying, is that if you’ve already taken a stance to never eat soy because it contains phytoestrogens, that you should add another 20 or so foods to that list as well for consistency. ALL of these foods should be on your no-eat list if you’re intending to prevent cancer, or prevent the growth of man-boobs. Are you shocked to learn that there are actually more phytoestrogen-rich foods other than soy? Foods that you’ve been consuming all this time without even knowing it!?

But wait….hold on a second. I haven’t told you if your fears are even warranted. Perhaps you don’t have to cut out your morning cup of Joe (because it contains phytoestrogens), or your weekend brewsky (because it contains phytoestrogens). Perhaps our concerns about the correlation between phytoestrogens and cancer are completely unwarranted. Have men truly ever grown breasts from eating too much soy? Let’s take a look at what actual science says.

First off, phytoestrogens belong to a large group of naturally occurring substances called natural phenolic compounds, of which coumestans, prenylflavonoids and isoflavones extert estrogenic effects. These are vastly different from human estrogens, or synthetic xenoestrogens such as PCBs, dioxins and BPA. By far, isoflavones from soy, and red clover as well as lignans from flaxseed have garnered the most research attention. Phytoestrogens bind to estrogen receptors (ER) and display an affinity for estrogen receptor beta (ER-beta) primarily. The reason they bind? Because they are the correct shape – they are a key that fits the lock well enough. There are other effects of phytoestrogens, but we’ll try to keep it simple for now. The key question here however, is whether all of this amounts to a significant clinical outcome.

Meta-analysis studies of phytoestrogens in men have concluded that neither soy foods, nor isoflavones affect levels of testosterone in men, nor do they affect sperm counts, create man breasts or otherwise make a man less manly. I’ve been eating non-GMO soy for years now and my wife will tell you that I’m even more manly than I was when she met me. True story.

Similar multi-study analyses have revealed a bit more convoluted picture when it comes to females however; but where phytoestrogens had zero effect in men, there is certainly an effect happening in women, but that isn’t to say it’s necessarily a negative outcome; quite the opposite in fact. Some studies have actually found cancer-protective effects of plant-based phytoestrogens (particularly estrogen receptor based cancers), and the studies that have shown risks with phytoestrogens and cancer have been primarily in vitro studies; that is to say – they only work in a petri dish on a lab nerd’s desk and thus far don’t translate to real women; as is the case with many in vitro studies. Other studies have actually found that higher intakes of phytoestrogens offer even greater protective benefits. I’m not making this stuff up, I don’t sell tofu, and no; I don’t own shares in soy stock.

Like any area of intense research, you will find that although studies may not always agree, there tends to be a particular pattern that emerges as studies tend to fall one way or the other as they accumulate. If there are 95 studies suggesting outcome A, and 3 studies suggesting outcome B, guess which outcome you tend to gravitate towards believing? While soy arguments will always devolve into a matter of cherry-picking studies to support a particular position (ahem), as of today, the majority of large studies and epidemiological reports suggest that in most cases, phytoestrogens have a cancer protective effect, with the prevailing theory suggesting that they compete with the body’s own naturally occurring estrorgens and therefore decrease excessive signalling in pre-menopausal women (decreasing cancer risk), and mildly stimulating estrogen receptors in menopausal women to lessen the symptoms of menopause. It’s a far-cry from the reports concerning medical hormone replacement therapy (HRT). And remember, way back at the beginning of this article, we pointed out that there are actually more phytoestrogen-rich foods other than soy – probably ones that you’ve been consuming without realizing it for years or even decades.

Soybean Sprouts by USBThinkingAhead licensed under CC BY 2.0

Now that I’ve explained my position about how I feel about phytoestrogens in general from ALL foods, allow me to clarify a couple of things specific to soy itself. I don’t’ think people should be concerned about the phytoestrogen content of soy as I don’t feel as though that is a reason to abstain – especially considering that phytoestrogens are found in a large variety of foods.

However, I do have a few significant beefs with soy. My primary concern is that the majority of soy produced today is genetically modified (GMO) and without going off on a wild tangent, let’s just say I’m not cool with this. I always make a point of buying non-GMO soy with the expectation and assumption that what I’m buying is in fact labelled and regulated correctly. Organic soy has to be non-GMO by criteria, so that’s another avenue my family and I pursue.

My last beef with soy is strangely less to do with soy, and more about the human immune system. When speaking of immune-related food intolerances, soy proteins are common allergens for a number of people (not everyone). However, getting angry at soy because of this fact would be like getting angry at your dog because he gives you the sniffles. Don’t blame the dog! Don’t blame the soy! Just because your body treats something harmless as something harmful doesn’t mean that it’s a nasty thing; merely that your immune system is whacked out. Yes – your immune system is overreacting and making you feel terrible. So if anything, blame yourself (kidding….sort of).

Well, I feel like I’ve carried on this topic long enough. If you’ve stayed with me this far I thank you for reading and I’d love to hear your comments below if you’d care to share. Like anything nutrition related, there’s a never-ending list of things to discuss, debate, and overturn as new information becomes available. Let’s keep it truthful!