Is Soy Bad…Or is that a Myth?

Soy is a hot nutrition topic so I thought we could do a little myth busting on a common question I get about soy: does soy give men Gynecomastia? (aka man-boobs). Because I’m a plant-based dietitian (though I work with patients on ALL diets), I really wanted to tackle some of these myths that keep circulating. This one is dangerous because it actually prevents men from including a very important food in their diets! I developed a real passion for this topic during my position as Chair a few years back with the Vegetarian Nutrition Dietetic Practice Group. Leading that organization was such a gift and I got to be surrounded by so many experts from around the country.

Soy, along with many other plant-based foods, contains “plant-estrogen,” aka “phytoestrogen.” There’s a popular concern that this compound might imitate human estrogen, potentially stimulating cancer growth… or throwing a wrench into male testosterone levels, leading to the spontaneous development of the dreaded “man-boobs” (not a term I personally choose to use but one I am asked about often). I’m here to sift through the research, providing you with a clear understanding. So, let’s address the burning question: Does soy give men Gynecomastia? (aka man-boobs)?

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What do the experts say?

Based on an analysis of current literature, the firm, evidence-based conclusion that the consumption of soy foods does not have an impact on testosterone levels. The consensus is based on a 2021 research analysis of the past two decades, concluding that neither soy nor isoflavone intake affects levels of total testosterone, free testosterone, estradiol, or estrone. Another research analysis demonstrated that soy foods or supplements containing 40-70mg/d of soy isoflavones had no impact on hormones and semen quality. Other studies have found that up to 150mg/day of soy isoflavones have no impact on estrogen levels. To put it in perspective, an entire block of tofu has only 100 grams of isoflavones. Two research studies have found that the consumption of the equivalent of 4 blocks of tofu or 9 cups of soy milk has been shown to have a feminizing effect on men, but that is a TON of tofu and soy milk!

Another controversial study showed a 19% decrease in testosterone in 12 participants after 4 weeks of consuming 56 grams of isolated soy protein daily. For reference, on average most people require between 60-80 grams of protein per day (based on body size).  That means that this small group of study participants was eating very large quantities of a processed soy source. My recommendation is not to do this; I would have advised against it even before I read the study.

The consumption of any food can lead to abnormalities; not just soy. It is always recommended to consume whole foods over heavily processed alternatives to avoid the over consumption of a singular nutrient. Overall, there is no concern around eating soy products, even daily. In fact, soy has so many health benefits that it should be classified as a superfood!

Soy as a superfood

The macro and micronutrient composition of soy is truly remarkable. The protein quality of soy is nearly identical to that of meat; it is low in carbohydrates (and therefore suitable for diabetics), and it contains both omega 3 and omega 6 essential fatty acids. Soy has been directly linked to improved cardiovascular health by assisting to lower LDL cholesterol and blood pressure, reducing arterial stiffness, and promoting vasodilation. In addition, the consumption of soy products may reduce rates of cardiovascular events, like heart attacks.

As if heart health is not convincing enough, the consumption of soy has also been demonstrated to be protective against cancer, including prostate cancer. There is some evidence that the isoflavones in soy may inhibit metastasis, the development of secondary malignant growths.

So, is the concern surrounding “man-boobs” a significant enough reason for men to avoid consuming soy and potentially miss out on its numerous health benefits? I would say not. The likelihood of developing “man-boobs” from soy consumption is almost unheard of, whereas cardiovascular disease and prostate cancer stand as prominent causes of mortality in the United States. Embracing a daily intake of soy is not only beneficial but actively encouraged for overall health.

Whole-food soy products such as tofu, soy milk, tempeh, miso, and edamame offer a wealth of health advantages, contributing to heart health and aiding in cancer prevention. It is essential to emphasize the positive impact of these whole-food soy sources. Conversely, caution should be exercised with soy isolates, particularly those containing added sweeteners or preservatives, and their consumption should be kept to a minimum. The overarching message remains clear: the potential concerns related to “man-boobs” should not overshadow the considerable health benefits derived from the consumption of soy.

Does soy give men Gynecomastia? (aka man-boobs)

Please remember that you likely eat plant estrogens every day. Soy may have a higher concentration of them, but a plant fiber called “lignans” found in many plant foods including seeds, whole grains, bran, beans, fruits , and vegetables also contain plant estrogens.  According to the Linus Pauling Institute, though most research on phytoestrogen-rich diets has focused on soy isoflavones, lignans are the main source of phytoestrogens in our general diets.  If you eat fruits, veggies, beans and whole grains and don’t have man-boobs yet, then you’ll likely be ok eating a little soy.

I have a hard time when someone is telling me they can’t eat soy (which has proven health benefits), but they’re chugging soda, alcohol, or eating sugary desserts.  You want to know what will more likely cause man-boobs? Too much chocolate cake and beer.

You can find research to support what you want it to- that is certain. I encourage you to seek advice from individuals who lack a financial stake in the subject they’re discussing. When it comes to questions regarding your health, please find a medical provider, registered dietitian, or researcher who can provide evidence-based insights. Don’t rely solely on advice from friends, nutrition enthusiasts, or Google who tells you to avoid soy because it gives you man-boobs…

Please reach out to me to schedule an appointment to discuss your nutrition needs if you have more questions about using soy foods in your diet.

Soy is a hot nutrition topic but despite controversial claims, soy is a health food that should be a part of your healthy, balanced diet. It is easy and delicious to include soy in your favorite meals, you can use soy milk in your smoothies, add tofu to your stir frys, and enjoy tempeh in your tacos. If you are still concerned about soy, just shy away from processed soy and focus on whole soy products like tofu, tempeh, soy milk, miso, and edamame beans. Soy is a superb complete protein that can help you to reduce your consumption of meat, increase healthy plant-proteins in your diet, and help you to live a happy, healthy life.

What do you think? This can be an emotionally charged and controversial topic – I’d love to hear your feedback and experience!