Is soy good or bad?

The Down Low on Soy – Is It Good or Bad?

There’s no doubt that soy is the subject of many debates.  All you need to do is Google soy and you’ll be gifted with thousands of blogs contradicting each other.  While one expert will say soy is bad and you should avoid it at all costs, another will tell you soy is perfectly fine.  Frustrating, right? 

Another concern that people have is estrogen and soy.  Many men feel soy will give them moobs (man boobs) and women are afraid soy will raise estrogen levels leading to estrogen dominant cancers. 

So…let’s have it out, shall we?  For those looking for a quick answer…soy’s bad rep is unjustified.  I’ll talk about why it’s gotten such a bad name, what it really does in the body, and how soy can be beneficial.

Some background on soy

Soybean crops are on the rise in the US.  They are second to corn and are quickly growing; they could eventually take the top spot.  Most soy is used for soybean oil (margarine, vegetable oil, lubricants for cars, etc).  The meal is used for animal feed.  So if you think soy if bad but you’re consuming grain fed animals, you’re not really avoiding soy…

It’s important to note that about 80% of soybean crops in the US are genetically modified organisms (GMO).  If GMOs don’t bother you, skip this section but keep reading the rest.  If they do, ensure you purchase organic soy products to avoid GMO soy.  If you’re interested in reading about herbicide and insecticide use in GMO crops, this is a good article to peruse. 

Animal studies are often used when looking at various aspects of science.  They are usually a good starting point but this is not the case when it comes to soy.  Mice metabolize soy isoflavones much different than humans do (2).  Any negative studies about soy in animals are studies that should not be taken into account. 

With that, let’s start with looking at some recent studies.  I only looked at peer-reviewed human based studies within the last five years.  I didn’t go back further because science is always changing. 

Soy and estrogen

Soy contains a component called isoflavones.  These isoflavones have a similar molecular structure to estrogen.  This is why soy may have estrogenic effects in the body and are called phytoestrogens.  Isoflavones is plural…there are many isoflavones and not just one.  Isoflavones are also known as selective estrogen receptor modulators (SERMs).  It’s important to note that common cancer medications such a Tamoxifen are also known as SERMs. 

Isoflavones have different effects in the body than estrogen.  Estrogen stimulates vaginal tissue growth but isoflavones do not (2).  Some feel estrogenic affects from soy because soy binds to estrogen receptors but soy is not actually acting in the same manner that estrogen is. 

Because we can sometimes feel the estrogen effects from soy, people correlate that with soy acting as estrogen.  This is where the moobs thought comes from.  Honestly, poor diet and lifestyle will cause moobs…not soy.

Soy’s role in breast cancer

I think many are concerned with breast cancer and soy intake.  This comes from poorly cited or written articles on the internet.  There are various styles of eating that are massively anti-soy and I feel they are picking and choosing their research to develop this opinion.  For every one trial that shows soy is bad, there’s another that shows soy is good.  This is why I use reviews…they look at all studies and formulate an opinion from those studies.

This particular review looked at well over 100 different studies relating to soy and breast cancer.  All the studies showed a decrease in breast cancer risk and development amongst individuals that consumed soy on a regular basis.  There were no studies found that showed an increased risk of breast cancer specifically from increased soy intake (1). 

Dietary patterns and environmental concerns probably play a larger role in the development of breast cancer than we care to give credit to.  Asians have the lowest risk of breast cancer.  However, when Asians move into North America or Europe, their risk rates increase (4).  This is a good indication that a processed diet plays a role. 

BOTTOM LINE:  Soy protects against breast cancer and does not feed breast cancer as some report.

Soy’s role in prostate cancer

Prostate cancer is the second common cancer in men world-wide (5).  It’s an androgen dependent organ with the most prevalent androgens being testosterone and DHEA, a precursor to both estrogen and testosterone.  For a while, many thought prostate cancer was a by-product of too much estrogen in the body.  And it very well could be.  Poor lifestyle and environment can cause an increase in bad estrogens in the body.  We also need a healthy liver to metabolize hormones.  If men consume a lot of processed foods and don’t really take care of the body, they will produce more estrogen and see a decline in their testosterone levels.  This could be one reason for developing prostate cancer.  And the leading cause of moobs. 

While it looks like soy isn’t going to help put active prostate cancer in remission, it can be helpful in preventing this type of cancer overall.  It was found that soy/isoflavone intake was prostate protective in men that were at risk of developing prostate cancer (5). 

Another review found that same stating “significantly lower incidence of prostate cancer among people who ingest more phytoestrogens” (6).  For this study, they correlated phytoestrogens with tofu and soybeans but not soy milk.  Interestingly, they found this was only applicable to Caucasians and Asians and there was no change in risk with African Americans.  There’s a possibility that genetics play a role there as well. 

BOTTOM LINE:  Soy protects against the development of prostate cancer but does not help put active prostate cancer into remission. 

Soy’s other benefits 

Soy protein can actually have cholesterol lowering effects.  Various studies have shown that as much as 25g of soy protein daily can lower LDL levels by up to 6% (3).  That’s a pretty significant decrease in the “bad” cholesterol levels.  On top of lowering the bad cholesterol, it was shown that soy can reduce circulating triglyceride levels by as much as 5% (3).  There was also a reporting increase in HDL; the “good” cholesterol. 

A few, small studies have shown that soy can be hypotensive (3).  While lowering blood pressure was not the focus of these studies, it was a pleasant side effect for some.  More studies are needed in this area before they can definitively say that soy is hypotensive.

Soy can also be protective against osteoporosis.  It’s been found that while tofu, specifically, if higher in calcium, it’s the isoflavones that help increase bone turnover in the elderly (3).  This helps to decrease fractures.  Natto, a fermented soy product, contains ample amounts of vitamin K2, an important bone nutrient. 


Now, some will also mention the antinutrients contained in soy.  Research in this area is very, very slim.  But you’ll find tons of people mentioning the antinutrients. 

Antinutrients are components of a food that prevent absorption of other nutrients.  For instance, legumes and grains contain an antinutrient called lectins.  Lectins, while not directly causing poor absorption of nutrients, can cause problems for som.  Lectins are plants internal defense mechanisms.  Without them, bugs and critters would eat them before we could.  Lectins can cause digestive concerns in some people but not all.  Since soybeans are a legume, presumably, they also contain lectins. 

Spinach contains phytic acid, an antinutrient.  Phystic acid can prevent the absorption of calcium contained in spinach. 

Now, does that mean we all need to avoid these foods because we may not absorb every last ounce of goodness in the food?  No.  This is a situation where the benefits outweigh the negative.  For some, avoidance may be necessary.  But for most, avoidance is just silly.


The benefits of soy are never ending.  I’ve never quite understood why it got such a bad rep.  The only thing I can think of is basing that information on poorly designed studies or studies based solely on mice. 

I do have one caution and that’s stick to mainly unprocessed soy and buy organic.  Organic soy is non-GMO.  I typically don’t recommend soybean oil and soy milk because those products are highly processed.  But I’m a fan of quality tofu, tempeh, miso, natto, and edamame.  Natto, tempeh, and miso are fermented soy so you get the gut health benefits from them as well.

So…tell me what you learned about soy from this blog.  Were you in the “soy is bad” camp?  Was there anything interesting you found in this blog?

Leave a comment below and let me know!


Fritz, H., Seely, D., Flower, G., Skidmore, B., Fernandes, R., Vadeboncoeur, S., … Fergusson, D. (2013). Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review. PLoS ONE, 8(11), e81968. (1)

Messina, M. (2016). Impact of Soy Foods on the Development of Breast Cancer and the Prognosis of Breast Cancer Patients. Complementary Medicine Research, 23(2), 75–80. (2)

Messina, M. (2016). Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature. Nutrients, 8(12), 754. (3)

Uifălean, A., Schneider, S., Ionescu, C., Lalk, M., & Iuga, A. C. (2016). Soy Isoflavones and Breast Cancer Cell Lines: Molecular Mechanisms and Future Perspectives. Molecules, 21(1). (4)

Zhang, H.-Y., Cui, J., Zhang, Y., Wang, Z.-L., Chong, T., & Wang, Z.-M. (2016). Isoflavones and Prostate Cancer: A Review of Some Critical Issues. Chinese Medical Journal, 129(3), 341–347. (5)

Zhang M., Wang K., Chen L., Yin B., & Song Y. (2016). Is phytoestrogen intake associated with decreased risk of prostate cancer? A systematic review of epidemiological studies based on 17,546 cases. Andrology, 4(4), 745–756.  (6)

Sunny Brigham, MS, CNS

I'm Sunny! I'm a board-certified clinical nutritionist with an MS in Clinical Nutrition. I help individuals reduce fatigue, eliminate bloat, and lose weight by healing the digestive tract and balancing hormones. I provide individual and group nutrition consultations nationwide. Grab my metabolism boosting guide!

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