Soy is a nutrient-dense, complete plant-based protein that may offer many protective benefits. Research suggests it may help protect against certain cancers, support heart health, and even ease menopause symptoms. It contains isoflavones, natural compounds with antioxidant properties that have been shown to reduce inflammation and improve bone health.

Yet, despite its many benefits, soy remains one of the most misunderstood foods. Misinformation has led many to avoid it due to concerns about breast cancer risk and hormonal effects in men. These concerns, fueled mainly by misinformation and poorly done studies, have overshadowed decades of research supporting soy’s safety and health benefits.

Is soy harmful?

The belief that soy is dangerous primarily stems from animal studies in which rats were given excessive amounts of soy. However, these studies fail to translate directly to humans as rats have many physiological and anatomical differences and metabolize isoflavones differently than we do.

Estrogens are a powerful hormone responsible for cell growth, particularly in reproductive tissues. Because isoflavones are structurally similar to estrogen, many assume they mimic estrogen’s effects. However, isoflavones uniquely bind to estrogen receptors, sometimes producing opposite physiological effects. This is why soy is linked to reduced breast and prostate cancer risk, fewer menopausal symptoms, and improved kidney function.

The nutrition of soy

Whole soy foods such as tofu, tempeh, and edamame are some of the most nutrient-dense plant foods available. Soy is considered a complete protein, providing all nine essential amino acids, making it an excellent protein source for vegetarians, vegans, or anyone looking to have a more diverse diet. It is also high in fiber, supports digestion and blood sugar regulation, and is high in micronutrients like iron, calcium, magnesium, and potassium- minerals crucial for maintaining strong bones, proper muscle function, and cardiovascular health.

Unlike animal-based proteins, which can contain high levels of saturated fat, soy contains polyunsaturated and monounsaturated fats, including omega-3 fatty acids, which are anti-inflammatory and heart-healthy.

Soy and hormones

One of the biggest misconceptions about soy is its impact on hormones, particularly in men. While isoflavones can bind to estrogen receptors, extensive research has found that moderate soy consumption does not lower testosterone, disrupt hormone balance, or impair reproductive health.

Concerns have arisen from a few extreme cases where individuals consumed excessive amounts of soy. For instance, one man drank 1.2 liters of soy milk daily for three years and developed hormonal imbalances, as did another man who ate over a pound of tofu daily. These cases are not representative of normal dietary intake.

In fact, soy may actually have beneficial effects on hormones in menopausal and postmenopausal women. Studies show that soy reduces menopausal symptoms, including hot flashes and vaginal dryness. A review found that soy reduced hot flashes by up to 84%, while another linked soy to improved vaginal health.

What the science says

Extensive research supports the safety and benefits of soy for both men and women. A large meta-analysis found that soy protein and isoflavones do not affect serum testosterone levels in men, and another review found that even large amounts of soy did not cause feminizing effects.

Regarding breast cancer, multiple studies have debunked fears about soy increasing risk and have, in fact, shown the opposite. A 2019 review found that women with a soy-rich diet were 16% less likely to die following a cancer diagnosis. Another study suggested that women who regularly eat tofu are 22% less likely to develop breast cancer. A 2024 study even found that soy isoflavones lowered breast cancer reoccurrence by 26%.  

Soy is also linked to lower risks of other cancers. A large study review found that soy-rich diets reduced overall cancer mortality by 10%. Another study review found soy reduced endometrial cancer by 19%. Studies also link soy to a lower risk of prostate cancer in men.

Beyond cancer, soy isoflavones may offer other health benefits. A 2020 review found that people who ate tofu regularly were less likely to develop type 2 diabetes. Other studies suggest soy improves bone density, reduces bone loss, and enhances brain function, including memory and processing speed.

Health benefits

Heart health

Some of soy's most documented benefits are its heart-protective effects. Research shows that soy protein can help lower LDL cholesterol (bad) while slightly increasing HDL cholesterol (good), reducing the risk of heart disease. Isoflavones have antioxidant properties, which may help improve blood vessel function and reduce inflammation, further supporting cardiovascular health.

Hormone balance

Despite persistent myths, studies show that soy’s plant-based phytoestrogens do not disrupt hormone levels in either men or women. In fact, soy may help ease symptoms of menopause, like hot flashes, and support bone density, reducing the risk of osteoporosis.

Cancer prevention

Diets rich in whole soy foods may also offer protection against cancer, particularly breast and prostate cancer. Contrary to outdated concerns, mostly involving poorly done studies, moderate soy consumption is protective against cancer, not harmful. Populations that consume soy regularly, as in many Asian countries, have lower rates of these cancers, and studies suggest that isoflavones may help regulate cell growth and reduce tumor formation. Studies show that consumption of soy foods early in life appears to be especially helpful for cancer prevention later in life.

Gut health

Fermented soy products such as tempeh, miso, and natto have prebiotic properties that can help nourish a healthy microbiome.

Concerns around soy foods

Perhaps the most important distinction to make when talking about soy’s health impacts is the difference between whole soy foods (such as edamame, tempeh, miso, and tofu) and highly processed soy products (such as soy protein isolates found in many meat substitutes, powders, and bars). Whole soy foods retain their beneficial nutrients and fiber, while ultra-processed soy derivatives may be stripped of these benefits and combined with additives. Ultimately, more research is needed to understand soy isolates fully.

One common concern is that most soybeans are genetically modified (GMO). More studies are needed to fully understand GMOs and their effects on our health. Those looking to avoid them can opt for organic or non-GMO-certified soy products, which are widely available.

Soy allergies can be another legitimate concern for some. While not as common as dairy or peanut allergies, a true soy allergy is a reason to abstain from soy. However, most people tolerate soy well, and many can outgrow soy allergies over time.

Bottom Line: Whole soy foods are a healthy addition to most diets

Despite persistent myths, extensive research confirms that whole soy foods are safe, nutritious, and beneficial for overall health. From heart health and hormone balance to cancer prevention and gut support, incorporating soy into a balanced diet can be a health-promoting choice.

Disclaimer: These statements in this blog post have not been evaluated by the Food and Drug Administration. The information provided here is for educational purposes only and should not be considered medical advice. It's essential to consult with a qualified healthcare professional before making any dietary or lifestyle changes.

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