Does eating Soy harmfully increase estrogen in your body?

By December 2, 2016 No Comments

Does eating Soy harmfully increase estrogen in your body?

Article by Andrea Cole, Registered Holistic Nutritionist

There is plenty of controversy over Soy and Soy-based foods in the media and depending where you look or who you ask, you can find just as much information and studies relating to how Soy is a protein-rich, healthy superfood as well as it being an endocrine disrupting, anti-nutrient danger.  These opinions and the findings of studies vary greatly depending on who is conductingor funding the studies and differing interests (omnivores vs. vegetarians, medical doctors vs. nutritionists, etc).  The majority of “studies” on humans have been observational, and therefore not scientifically valid.  One of our biggest questions at The Healthy Butcher and is around Phytoestrogen.  Specifically, do the Phytoestrogens in soy cause hormonal issues in our bodies? I’ll explain what Phytoestrogen is and why there is a cause for concern.

A Phytoestrogen is defined as “any group of non-steroidal substances found in plants, including Isoflavones, that are structurally similar to estrogen and can mimic or modulate the action of endogenous estrogen when ingested by humans and other animals”(1).   It is the Isoflavone content in soy that constitutes it being a Phytoestrogen, specifically Genistein, Daidzein and Glucitein.  These Isoflavones are similar in molecular structure to the hormone Estrogen and as a result they have effects of stimulating the estrogen receptors in human cells (called the “estrogenic effect”) (2).   Bottomline, they can disrupt your body’s normal function.  Just how much they disrupt your bodily function depends on a host of factors, including the amount of Phytoestrogen already in your body and a slew of genetic factors (3).  I should note that the majority of external estrogen is consumed from milk and factory-farmed meat (where it is common to feed GMO Soy as a major part of their diet).

Historically, Isoflavones first came to the attention of scientists in the 1940’s because of breeding problems in female sheep in Australia grazing on a type of clover rich in Isoflavones.  Twenty years later, it was established that isoflavone-rich soy fed as part of the diet to cheetahs in North American Zoos was a factor in the decline in their fertility (4).   In the 1950’s, Isoflavones were being studied by the animal feed industry as possible growth-promoters because of reported estrogenic effects.  In the 1960’s, soy isoflavones were established as Phytoestrogens because of their binding affinities to estrogen receptors (5).

On the positive side, some studies have found that consuming phytoestrogens can have protective factors including reducing symptoms of menopause and hormone-sensitive cancers and some studies have found possible cholesterol-lowering effects.  The Soy industry has largely promoted Soy as a health food as it is high in protein, low in fat and containing the full amount of amino acids making it a complete protein as well as containing Iron, Vitamins B and C, Magnesium, Folate, Niacin and Zinc.  Now, there is an issue with absorption of these nutrients due to the Phytic acid content like in many nuts, seeds and legumes, but that’s a whole other article.

On the negative side, according to the Weston A. Price foundation, the negatives outweigh the positives when it comes to Soy.  They list a myriad of health issues including the potential to reduce fertility, promote breast cancer, accelerate brain decline, contribute to hypo-thyroid and thyroid cancer, trigger early puberty, disrupt development of fetuses, affect erectile function and depress the immune function (6).  They also state that in infants fed soy milk formula there is a link to auto-immune and thyroid disease as well as early puberty and fertility issues later in life (7).  A recent article in Scientific American compares the main isoflavone in soy, genistein to BPA’s which are known xenoestrogens found in plastics that are linked to brain harm and reproductive disruptions (8).  There is controversy over the validity of these statements, and the Soy industry spends money on debunking these studies and funding ones with more positive outcomes.  Make no mistake about it, the Soy industry is a massive one and Soy is found in more foods than you think (9), so the economic impact is significant.

Of main concern to me as a Nutritionist, and us here at The Healthy Butcher and is the large amount of soybean oil and soy protein isolate in our food system today.  Soy ingredients are in more than 60% of processed and packaged foods and in nearly 100% of fast foods (10).  These ingredients are things like flavourings, preservatives, emulsifiers and sweeteners and are found in things like meal replacement bars, chocolate bars, soups, sauces, meat alternatives, cereals, bullion, ice cream, bakery products and bread and are also called Textured Vegetable Protein (TVP), Lecithin, “Natural Flavour”, MSG and Mono and Diglyceride.  These processed “foods” with heavy marketing lead to overconsumption of something that isn’t meant to be consumed at all.

So I arrive at my conclusion, which is the same conclusion I come to in most of my articles.  Eat real, whole foods and don’t worry about over analyzing the nutritional content!  Traditional ways of consuming soy, like organic whole soybeans (edamame) or fermented soy like tempeh, miso, natto and soy sauce have been consumed as part of a healthy traditional Asian diet for countless years and the consensus from many doctors and nutritionists is that these are a safer, healthier choices.  In general, it’s hard to go wrong with whole, organic, unprocessed foods in balanced amounts.  Problems typically occur with processed food in all forms, including Soy.



(1) The American Heritage Medical Dictionary.  Houton Mifflin Company, 2007.
(2)   Andrew, Ryan.  Precision Nutrition Inc. Soy:  The Latest Research.  Web. Nov 2016.
(3) Ibid.
(4) Mesina, Mark.  The Journal of Nutrition:  A Brief Historical Overview of the Past Two Decades of Soy and Isoflavone Research.  California, 2010.  J. Nutr. 140: 1350S–1354S, 2010.
(5) Ibid.
(6) Nienheiser, Jill.  The Weston A. Price Foundation.  Studies showing adverse effects of Soy, 1939-2014.  August 2003.  Web. Nov. 2016.
(7) Ibid.
(8) Konkel, Lindsey.  Environmental Health News.  Could Eating Too Much Soy Be Bad For           You?  Nov 2009.  Web.  Nov 2016.
(9) The US is one of the largest producers of soy worldwide (55%) and 90% of soy crops are GMO.  Andrew, Ryan.  Precision Nutrition Inc. Soy:  The Latest Research.  Web. Nov 2016.
(10) Daniel, Kaayla.  The Weston A. Price Foundation.  Response to Dr. Mark Hyman.  Soy:       Blessing or Curse? Sept. 2010.  Web.  Nov 2016.