The Truth About Soy

Group of Edamame soy beans shelled on white background

Many vegans and vegetarians can attest that when your lifestyle is divulged to a group of people, for example at a luncheon or dinner party, it often becomes the topic of conversation throughout the event. It’s difficult to avoid, since veggie menu options are often limited at restaurants – when you order a Caprese salad with no cheese, add avocado you pretty much give yourself away. This is a blessing! These are opportunities to inform others and share your reasons for keeping animal products off your plate, and usually a great time to dispel some common myths about plant-based diets.

Recently at dinner my friend Carla asked me about soy. Soy has made a name for itself in the field of nutrition and unfortunately it’s a hugely misunderstood food. Either you love soy, or you think it’s the devil reincarnate, the cause of all cancer, disease, and manboobs.  We’re going to dive right into dispelling the most common myths about soy, using REAL SCIENTIFIC EVIDENCE. One of the biggest problems about health and nutrition information today is that we all believe everything we read on the internet, see on the news, or hear from a friend who has some letters after his/her name. If we want to be informed and critical consumers, we must verify health claims with a credible source. Your credible source could be different from Joe’s credible source, but generally I’m talking about a legitimate organization whose main goal is to perform or share evidence-based research with an unbiased, scientifically sound, peer-reviewed process. Also be wary of famous doctors who make millions of dollars touting the benefits of single ingredients that you MUST put in your smoothie if you are to live another day. This is a form of reductionism and it’s a dangerous way to view the world.


The most common myth about soy is that it increases the risk of breast cancer. The theory behind this involves isoflavones, which contain phytoestrogens, which are mildly similar to estrogens. It’s well-known in medicine that giving post-menopausal women exogenous estrogen increases their risk of breast cancer. Is soy mentioned anywhere here? Nope. Again, someone used a reductionist worldview and decided that since estrogen seems to increase breast cancer risk in post-menopausal women, and that some women with breast cancer have estrogen-sensitive tumors and benefit from an estrogen-blocking drug called tamoxifen, it MUST be true that phytoestrogen-containing soy products are bad for breast cancer. This assertion undermines the complexity of the human body, so we’re going to dispel this one fairly quickly. There have only been 3 major studies since 2009 investigating soy and breast cancer recurrence and survival rates. All three of them have favored soy, and particularly the isoflavones in soy, and found that women with the largest intake of isoflavones had the lowest rates of breast cancer recurrence. Here are the studies:

  • The 2009 LACE study (Life After Cancer Epidemiology) study, followed 2000 breast cancer survivors were followed for 9 years. Post-menopausal women on the estrogen-blocking drug tamoxifen, who had the most isoflavones in their diet had the lowest levels of cancer recurrence (1).
  • A 2009 population based cohort study by JAMA (the Journal of the American Medical Association) studied over 5000 women in China who were breast cancer survivors and found that the more soy these woman consumed, the less likely they were to have a recurrence of breast cancer, and the less likely they were to die from breast cancer (2).
  • A 2011 study published by the American Association for Cancer Research studied the diet of over 3000 breast cancer survivors. Isoflavone intake was associated with a reduced risk of breast cancer recurrence and a reduced risk of death from breast cancer (3).

What if I’ve never had breast cancer? How will soy affect me? Population studies have long shown that countries with higher intake of soy (like many Asian countries) have lower rates of many diseases including breast cancer, prostate cancer, cardiovascular disease, and bone fractures (4).  A critic may argue that “genetics” could be to blame, but these studies also find that when Asians emigrate to Western countries, their disease rates change. Hence, when they adopt a more Western diet, which is typically lower in soy products, they lost the health-protective benefits of soy.


This is just plain false! There are no legitimate studies to support any link between soy intake and the development of gynecomastia (aka manboobs). While gynecomastia is thought to be caused by an imbalance of testosterone and estrogen, remember the isoflavones in soy do NOT contain estrogen. They contain phytoestrogens which bear structural resemblance to estrogens but are not the same, nor do they function the same in the body once ingested.


The jury is still out on GMOs. Nobody likes them, but from a health perspective we don’t really have a great reason to hate them yet. I don’t believe GMOs are the cure for world hunger (but veganism could be), and I see them as a little symbol of evil in this country where agribusiness and government spoon each other to sleep each night. I dislike GMOs because they are the bread and butter of Monsanto, a company that has completely taken over agriculture in a way not far off from how King Henry the VIII ruled England. In short, not all soy is genetically modified. In the US and Canada, certified organic soy is not allowed to be GMO, so just buy organic and you’re all good.


Can I just say I despise the term “hormone disruptor?” Its a word commonly used by nutritional fear-mongers to sound scientific. Lets agree to never use it again! Now that we’ve touched a bit on estrogen and phytoestrogen in MYTH #1, here we will just fine tune what we know about soy and estrogen. Things are about to get a little complicated, so if you’re still with me I highly recommend you check out this video by Dr. Michael Gregor where he explains the complex relationship between phytoestrogens, estrogen, and the tissues in our body. Dr. Gregor explains these relationships so eloquently that I feel compelled to only summarize his words with this: the human body is complex and beyond our full understanding.

Thus far, we have little to no reason to believe that soy is bad for us, in fact it seems to be good for us. It lowers our risk of breast and prostate cancer, reduces fracture risk, and protects against cardiovascular disease. Soy is a complete protein, meaning it contains all the essential amino acids we need. It is also low in fat and high in other beneficial nutrients like lignans, antioxidants, and inhibitors of angiogenesis. We can live our entire lives attaching labels to foods and creating fear and doubt about which foods to eat and which foods to avoid, or we can look at the latest evidence available and make an educated decision, realizing that science is ever-changing and the true scientists in this world are dedicated to sharing the current information and in constant search of more evidence and knowledge to better our understanding of life and how to protect it.

❤ Christina



(1) Guha N, Kwan ML, Quesenberry CP Jr, Weltzien EK, Castillo AL, Caan BJ. Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study. Breast Cancer Res Treat. 2009 Nov;118(2):395-405.
(2) Shu XO, Zheng Y, Cai H, Gu K, Chen Z, Zheng W, Lu W. Soy Food Intake and Breast Cancer Survival. JAMA. 2009 Dec 9;302(22):2437-43.
(3) Caan BJ, Natarajan L, Parker B, Gold EB, Thomson C, Newman V, Rock CL, Pu M, Al-Delaimy W, Pierce JP. Soy food consumption and breast cancer prognosis. Cancer Epidemiol Biomarkers Prev. 2011 May;20(5):854-8.
(4) Barrett, JR. The Science of Soy: What do we really know?
*photo courtesy of



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