Happy National Soy Foods Month! In honor of a month focused on a healthful food item, I thought we could do a little myth busting on one of the most common questions I get about soy: does it give men man-boobs?
Because I recommend a plant-based diet to my patients at work and hold a position with the Vegetarian Nutrition Dietetic Practice Group as their incoming Chair-Elect, the topic of soy is something I discuss everyday. Soy (among many other plant foods) contains “plant-estrogen” aka “phytoestrogen” which people fear mimics human estrogen and can stimulate cancer growth…..or dominate a male’s testosterone levels which would promote the spontaneous development of the dreaded man-boob (not a term I personally choose to use but one I am asked about often).
Based on an analysis of the current available literature on the effects of soy on testosterone levels, I have come to the conclusion that the answer is: No, you will not develop man-boobs if you are a male consuming soy. Click To Tweet There are many reviews of studies done and one consensus I would like to highlight is: “These recent studies in men consuming soyfoods or supplements containing 40–70 mg/d of soyisoflavones showed few effects on plasma hormones or semen quality. These data do not support concerns about effects on reproductive hormones and semen quality”.
While research shows that soy consumption does not cause hormonal disruption or imbalance, it does have research pointing to its positive effects in regards to cancer-prevention and cardiovascular health. As with any food, I always discuss the importance of moderate consumption of all foods with my patients. That means a soy product once every day or several times per week instead of at every meal. Further, soy is a highly genetically modified crop in this country and many of my patients prefer to buy organic in the hopes of decreasing their exposure to genetically modified foods. Finally, I prefer whole food sources of all products eaten and suggest consuming unprocessed/less processed soy such as edamame, tempeh, or miso instead of more processed products such as soy protein isolate (especially with added sweeteners or preservatives).
There are some small and controversial studies that show a decrease in testosterone with high levels of concentrated soy protein isolate such as one from 2007 showing a 19% decrease in mean serum testosterone levels in 12 men over a 4-week period after consuming 56 grams daily of isolated soy protein. 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.
Please remember that you likely eat phytoestrogens (plant estrogens) every day. Soy may have a high concentration, but a plant substance called “lignans” (basically a type of fiber) is found in many plant foods including seeds (flax, pumpkin, sunflower, poppy, sesame), whole grains (rye, oats, barley), bran (wheat, oat, rye), beans, fruits (particularly berries), and vegetables. 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. Further, 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 listen to people without a financial interest in the topic they are educating you on and when you need an answer regarding your health, please find a medical provider, registered dietitian or researcher who can provide you a research-based answer and not just a friend, nutrition enthusiast, or Google who tells you to avoid soy because it gives you man-boobs…..
What do you think? This can be an emotionally charged and controversial topic – I’d love to hear your feedback and experience on the matter!
Ginger Hultin,MS, RD, CSO
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