The most common question I get from clients during nutrition consultations is about the safety of soy.
Hands down, the answer is yes – soy is safe to eat! But don’t take my word for it – let the facts speak for themselves. This blog is dedicated to helping you feel confident that soy-based foods not only are safe to eat but are one of the most nutrient-packed and health-promoting foods you can include in your diet.
What is soy?
Soy foods include edamame (baby soybeans that resemble peas or lima beans), tofu, tempeh (soybean curd), miso (soybean paste), and soymilk to name a few. All soy foods come from the soybean – a legume that is widely grown in the United States, Brazil, Argentina and India (Voora et al., 2020). While soy foods are widely available and enjoyed by many around the world, they are a most common element of Asian diets. The types and amounts of soy foods consumed vary within different regions and countries in Asia, however studies suggest that most people living in Asia consume about 8-10g of soy protein per day, with some eating up to 25g per day! (Messina, 2016a)
What are the nutritional benefits of soy foods?
First and foremost, soy foods are an excellent source of plant-based protein. Unlike most other plant-based proteins, soy protein is considered a “complete” protein. What does this mean? It means that soy protein contains all nine essential amino acids, or building blocks, that our body needs to create muscles, other body tissues, hormones, etc. It’s similar to having all the vowels when playing Scrabble because it means you can make the most words. This makes soy protein the best plant-based alternative to meat in your diet.
Compared to animal-based sources of protein such as red meats and poultry, soy foods are generally lower in saturated fats and higher in fibre. This is great for keeping your heart healthy, which we will discuss in detail later on.
Soy foods are also jam packed with many vitamins and minerals, such as B-vitamins, calcium, zinc and iron (Harvard, 2022).
What’s all the concern with soy about?
The ongoing concern about soy relates to the mistaken belief that soy disrupts hormones in the body because soy foods contain isoflavones, a naturally occurring plant-based compound unique to soy. Isoflavones have a similar chemical structure to the hormone estrogen, which our body naturally produces. This means that, through a very long and complex process, isoflavones can mimic how estrogen works in your body, but they don’t always have this effect (Harvard, 2022). This has created a common misconception that eating soy foods disrupts your body’s natural hormone production and response, however current research shows that this is not true (Messina, 2016b). The very few studies that have suggested that isoflavones have a negative effect on hormone production have been completed on animals (not humans!) and provided isoflavones in much higher amounts than you would get from a normal-sized portion of soy foods (Messina, 2016b).
Let me assure you, nothing bad will happen to you by including soy foods in your diet. This is proven by a vast amount of research about soy over the last decade that debunks the lingering myths about soy and speaks highly of the health benefits.
How do we really know that soy is safe to eat?
Like most research, results from one study to the next may vary so when we examine the evidence, it’s important to look for the cumulative results of high-quality studies to see the key results that emerge and stay consistent about a particular topic. The more studies done on the same topic with the same results = better strength of evidence and confidence in knowing that something really is true. This is how something about nutrition or any health-related topic becomes a “fact” – it does not come from personal experience, opinion, or hearing your neighbour proclaiming something to be true.
In the following sections, we dig deep and talk about what we know about soy foods based on the most current research so once you’re done reading, you can click off this page in confidence knowing the answer to the age-old question: Is soy safe to eat?
Soy & Heart Health
As mentioned earlier, eating soy foods has been shown to keep your heart healthy and lower your overall risk for heart disease by improving levels of cholesterol and fats in your blood (Messina, 2016b). A recent study shows that soy proteins are the most beneficial when they replace animal proteins in your diet (Jenkins et al, 2010). In fact, consuming 25g of soy protein daily has been shown to lower cholesterol by 4-6% (Messina, 2016b). Soy foods can also help to lower your blood pressure, which may help prevent a stroke or heart attack (Messina, 2016b). Isoflavones in soy foods help to lower blood pressure by causing “vasodilation” - when the walls of your blood vessels relax and become wider in diameter. This makes it easier for your blood to flow through your blood vessels, which decreases the blood pressure in those veins (Ramdath et al., 2017).
Soy & Bone Health
A hormone called estrogen serves many roles for women’s health including helping to keep bones strong. When estrogen levels become low, like during menopause, it may cause low bone density which may lead to osteoporosis and bone fractures (Messina, 2016b). Regularly eating soy foods might help women during their menopause years maintain healthy and strong bones thanks to the positive effects of the isoflavones found in soy. Isoflavones “trick” your body into thinking it has more estrogen, which may be why studies show that women who regularly consume soy are 30% less likely to experience a bone fracture (Messina, 2016b). More research is needed to confirm the positive effects of soy foods on bone health, but the high-quality protein, calcium and other minerals found in soy foods will surely help keep your bones healthy and strong! (Messina, 2016b)
Soy & Menopause
Hot flashes are the most common complaint I hear from my female clients when they are going through menopause. Hot flashes happen in response to the changes in hormone levels during menopause and can quickly make a good day or deep sleep turn bad. The good news is that soy foods may help control the intensity and frequency of hot flashes (Messina, 2016b). Studies suggest a minimum of 40mg of isoflavones every day is needed to improve symptoms of hot flashes (Messina, 2016b). This is equal to about two cups of soy milk or 6oz of tofu. Another option may be to take an isoflavone supplement to help control hot flashes (Chen, 2019), but more evidence is needed to confirm this. Without a doubt, choose food first but supplements can play a role to provide a therapeutic benefit, when needed.
Soy & Men’s Health
I have taught nutrition to fitness students for the past 14 years and common concerns I’ve heard from my students are about soy causing damage to sperm and that eating soy will cause men to grow “man boobs.” This stems from how isoflavones can mimic how estrogen works in your body, which has created the idea that eating soy will negatively affect male fertility or cause “feminine” features to develop. This is simply not true! Research has shown that consuming moderate amounts of soy has no effect on male fertility (Messina, 2016b; Beaton et al., 2008; Hamilton-Reeves et al., 2010). Same thing goes for male “femininization,” the most common side effect of this being “gynecomastia” or excess fat tissue in the breast area caused by an increase in estrogen levels. Again, the idea is that the isoflavones in soy foods will mimic higher estrogen levels and cause these features to develop. There have been published stories of this, but these are isolated cases (remember: less studies = weaker evidence) and resulted from eating soy in amounts much, MUCH higher than one would get from eating moderate amounts of soy (Messina, 2010). Rest assured; current research shows that eating moderate amounts of soy foods does not have feminizing effects on men (Messina, 2010).
Soy & Breast Cancer
It is a common myth that individuals with breast cancer should avoid eating soy foods. This is absolutely not true! We do know that higher levels of estrogen can increase risk of breast cancer or may affect prognosis of those living with breast cancer, which again brings in the idea that the isoflavones in soy foods may cause the same effect. We also know that while isoflavones are similar to estrogen, they are not the same and do not have the same effect on breast cancer risk. There is no strong evidence that suggests that the isoflavones in soy foods have any negative effects on breast health (Messina, 2016b). It actually suggests the opposite! Consuming soy foods, especially during childhood and adolescence, can reduce risk of breast cancer by up to 60% (Messina, 2016b). For those already diagnosed with breast cancer, you can safely consume soy foods in moderation. In fact, there is research that shows that consuming soy foods can prevent recurrence and improve how well treatments work (Messina, 2016b).
Soy & Thyroid Health
If you have a normal working thyroid, research shows that soy foods are perfectly safe to eat. But if you are taking medications to help treat an underactive thyroid, eating soy foods may affect how well that medication works, specifically Synthroid (or levothyroxine). Despite this, people with low thyroid levels or “hypothyroidism” do not need to steer clear of soy foods completely – they just need to be careful when they consume them relative to their medication. The current recommendations for those taking Synthroid is that this medication is taken on an empty stomach (Messina, 2016b). In other words, if you take Synthroid in the morning before breakfast, you may want to skip the soy milk in your smoothie but feel free to have a glass for lunch or enjoy tofu at dinner.
Are there any other health conditions soy may help with?
Among all of the other amazing health benefits we’ve talked about already, there is some new research that shows soy’s potential benefits for other conditions, including mental health. We know that women, especially those in menopause, are two times more likely to be diagnosed with depression than men, which brings up the new idea that reproductive hormones may play a part in this. Some research shows that 100mg of isoflavones per day, in addition to medications, can reduce symptoms of depression (Messina, 2016b).
Very new research has shown that isoflavones can maintain and improve skin health and reduce wrinkles, but more research is needed to confirm this (Messina, 2016b).
Needless to say, the research is quite clear: Soy foods are safe and good for you!
But I don’t like the taste of soy foods like tofu!
If your qualm is less about the safety of soy but more about the taste (or should I say, lack thereof, as many of my clients have expressed), then you may be happy to know that soy foods like tofu and edamame absorb the flavours of others things really well so it’s all about how you prepare them.
Here are our top 3 recommended recipes featuring soy foods that will have you craving soy foods in no time:
How else can I include more soy in my diet?
First of all, be sure to stick to whole or minimally processed soy foods such as tofu, edamame, or soy milk instead of highly processed soy foods made from soy protein isolate (e.g. soy meat alternative products or protein powders) because they can lose as much as 90% of their isoflavone content during processing (Hollins Martin, 2013).
Here are some easy ways to boost your soy intake:
1. Have edamame as snack or add to your favourite salads
2. Try cooking a stir-fry with tofu instead of meat
3. Swap cow’s milk for soy milk in your cereals, coffee or tea
4. Add edamame to your next veggie sauté
5. Use soy milk for your next smoothie or smoothie bowl. Have you tried our TropiKale smoothie?
What’s the bottom line about soy?
Whole soy foods, such as tofu, tempeh, edamame, and soy milk make for a delicious and nutritious addition to your diet. The research is clear - it’s safe and beneficial to enjoy soy-based foods on a regular basis as part of a healthy diet.
For general preventative health, have soy foods at least 2-3 times each week. If you’re dealing with a health condition such as high cholesterol, menopause, or osteoporosis, have at least one or more servings of soy foods daily.
Feeling uncertain about the right amount of soy for you or how else to use nutrition to support your health?
This blog was written together by Jodi Robinson, RD and Jenna Leixner, virtual assistant and content creator for Craving Health.
Jodi Robinson, RD
As lead dietitian & founder of Craving Health, Jodi is a healthy eating coach who helps busy people clear their confusion about healthy eating and discover simple and sustainable meal and snack solutions. She is most passionate about helping her clients overcome disordered eating and the yo-yo dieting cycle. She believes life is too short to be held hostage by food and loves nothing more than helping her clients find the food freedom they deserve.
Beaton, L. K., McVeigh, B. L., Dillingham, B. L., Lampe, J. W., & Duncan, A. M. (2010). Soy protein isolates of varying isoflavone content do not adversely affect semen quality in healthy young men. Fertility and sterility, 94(5), 1717–1722. https://doi.org/10.1016/j.fertnstert.2009.08.055
Chen, L. R., Ko, N. Y., & Chen, K. H. (2019). Isoflavone Supplements for Menopausal Women: A Systematic Review. Nutrients, 11(11), 2649. https://doi.org/10.3390/nu11112649
Hamilton-Reeves, J. M., Vazquez, G., Duval, S. J., Phipps, W. R., Kurzer, M. S., & Messina, M. J. (2010). Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis. Fertility and sterility, 94(3), 997–1007. https://doi.org/10.1016/j.fertnstert.2009.04.038
Harvard T.H. Chan School of Public Health. (2022, January). Straight Talk About Soy. https://www.hsph.harvard.edu/nutritionsource/soy/#:~:text=Soy%20is%20unique%20in%20that,estrogenic%20or%20anti%2Destrogenic%20activity.
Holins Martin, C.J., Watson, R.R., & Preedy, V.R. (2013). Nutrition and Diet in Menopause. Humana Press. 10.1007/978-1-62703-373-2
Jenkins, D. J., Mirrahimi, A., Srichaikul, K., Berryman, C. E., Wang, L., Carleton, A., Abdulnour, S., Sievenpiper, J. L., Kendall, C. W., & Kris-Etherton, P. M. (2010). Soy protein reduces serum cholesterol by both intrinsic and food displacement mechanisms. The Journal of Nutrition, 140(12), 2302S–2311S. https://doi.org/10.3945/jn.110.124958
Messina. M. (2010). Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertility and sterility, 93(7), 2095–2104. https://doi.org/10.1016/j.fertnstert.2010.03.002
Messina, M. (2016a, June 3). Soy Plays Important Role in Asian Diets, But Consumption Varies Among Countries. Soy Nutrition Institute Global. https://sniglobal.org/soy-plays-important-role-in-asian-diets/
Messina, M. (2016b). Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature. Nutrients, 8(12), 754. https://doi.org/10.3390/nu8120754
Ramdath, D. D., Padhi, E. M., Sarfaraz, S., Renwick, S., & Duncan, A. M. (2017). Beyond the Cholesterol-Lowering Effect of Soy Protein: A Review of the Effects of Dietary Soy and Its Constituents on Risk Factors for Cardiovascular Disease. Nutrients, 9(4), 324. https://doi.org/10.3390/nu9040324
Voora, V., Larrea, C., & Bermudez, S. (2020, October). Global Market Report: Soybeans. International Institute for Sustainable Development. https://www.iisd.org/system/files/2020-10/ssi-global-market-report-soybean.pdf
