Soybeans are legumes rich in nutrients like protein, fiber, healthy fats, vitamins, and minerals like potassium, magnesium, folate, and iron. Soy is the base of many popular foods, including tofu, tempeh, soy sauce, soy milk, and many plant-based meat alternatives.

Some people have concerns about soy, as it can affect hormone levels in the body when consumed in very high amounts. However, studies show nutritious soy foods are safe to eat in typical amounts and can support health in several ways.

Soy contains isoflavones, which are a type of phytoestrogen. Phytoestrogens mimic the effects of the hormone estrogen in the body. Phytoestrogens can have either estrogenic or antiestrogenic effects, meaning they can either block estrogen absorption or have weak estrogenic activity. 

Due to soy’s impact on estrogen, some people think that eating soy may affect hormone levels, but research shows that eating moderate amounts of soy (25 grams per day or less) doesn’t have a significant impact on hormone levels in men or women.

Eating higher amounts of soy can impact hormone levels and may lead to conditions such as low testosterone and erectile dysfunction in men, so it’s best to avoid large amounts of soy.

Soy isoflavones also have goitrogenic activity. Goitrogens are compounds that interfere with the production of thyroid hormone. Some research suggests that high soy intake may lead to a slight increase in thyroid-stimulating hormone (TSH), which indicates a drop in thyroid hormone production. However, soy intake is unlikely to affect thyroid function in people without related health conditions.

Soy inhibits the absorption of the thyroid hormone replacement medication levothyroxine (under brand names Synthroid, Tirosint, and Unithroid). It is recommended to take thyroid medication on an empty stomach because food in general and certain supplements interfere with thyroid medication absorption.

If you have thyroid disease, it’s best to avoid taking in large amounts of soy, especially if your diet is low in iodine. Research shows that high soy consumption may increase the risk of developing hypothyroidism in people with iodine deficiency.

Soy foods are generally safe for most people to consume. However, people who are allergic to soy need to avoid all soy products, including edamame, soy milk, and soy protein powders. 

Studies show that eating soy may benefit health in several ways, including supporting heart health, decreasing breast cancer risk, and improving muscle mass. Benefits of soy include:

• May promote muscle growth: Eating soy products, like soybeans and soy protein powder, may boost muscle growth. A review of nine studies found that soy protein increased muscle mass and strength similar to whey protein and other animal proteins.
• May support weight loss: Protein is the most satiating nutrient, and adding soy protein sources to your diet could help you lose excess body fat.
• May lower the risk of certain cancers: Due to its effect on estrogen, soy may help protect against hormone-mediated cancers, such as certain types of breast cancer. A research review found that women with the highest soy intake had a 12% reduced risk of breast cancer compared to women with the lowest intake. Soy foods may also protect against prostate cancer.
• May reduce heart disease risk: A recent study found that soy isoflavone intake was associated with a lower risk of overall heart disease and coronary heart disease in adults. Soy may help lower heart disease risk factors, like high cholesterol.
• May ease menopause symptoms: Some research findings suggest that a soy-rich, plant-based diet may reduce the frequency and severity of hot flashes in postmenopausal women. However, more research is needed.

Eating soy foods may also benefit bone health and delay cognitive decline, but more research is needed to confirm these potential effects.

Traditional soy foods are made from whole soybeans that don’t undergo extensive processing. They also include fermented and unfermented soy products.

Fermented soy foods include natto, soy sauce, tempeh, and miso. Unfermented soy foods include whole soybeans, soy milk, tofu, fresh edamame, soy nuts, and soybean sprouts.

There are also processed soy foods, which undergo extensive manufacturing and are typically less nutritious than unprocessed soy foods. Processed soy foods include soy-based meat replacements like hotdogs, soy milk ice cream, soy-based cheeses, and soy-based snack foods like chips. Soy protein powder is another type of processed soy product. 

Some research shows that organically grown soybeans have significantly higher levels of protein, zinc, and several amino acids than conventionally grown soy. Also, commercially grown soy contains high levels of glyphosate, a pesticide that is harmful to human health.

While soy is generally safe for most people, it’s important to choose nutritious soy products.

Unprocessed soy products, like edamame and tofu, are more nutritious than processed soy products, like soy-based ice cream and soy-based meat replacements. Processing often removes some of the nutrients from the original food, and some processed soy foods can be high in ingredients like salt and added sugar.

For the most health benefits, eat whole soy foods in moderation as part of a well-rounded, nutrient-dense diet that’s also high in other foods, like fruits, vegetables, nuts, seeds, and fish. 

If you have questions about soy foods, including how to add them to your diet and whether soy is the right choice for you, consider speaking with a healthcare provider, like a registered dietitian.

Health concerns about soy stem from its effect on estrogen levels in the body. While eating high amounts of soy may affect hormones, particularly in people with thyroid disease, eating moderate amounts of soy is not harmful to health.

Whole soy foods, like edamame and tofu, are generally safe and nutritious for most people. When included as part of a balanced diet, soy foods can promote muscle growth, protect heart health, and support weight management.