Soy is one of the most controversial foods due to concerns about its potential impact on hormones and fertility. There are widespread myths about the health implications of soy foods, which has caused many people to steer away from this nutritious food. A deeper understanding of soy nutrition, specifically related to phytoestrogens, can help individuals and families make better-informed food choices for their health.
Phytoestrogens are naturally occurring plant compounds that resemble estradiol, a form of estrogen produced in the body. The body’s estrogen receptors treat phytoestrogens similarly to the hormone estrogen, either mimicking or blocking the body’s natural estrogen. There are two main types of phytoestrogens: isoflavones and lignans. Isoflavones are primarily found in soy products and have the most significant estrogen-like effects. Lignans are found in flaxseeds, sesame seeds, beans, wheat, oats, peaches, berries, garlic, broccoli and carrots among other foods.
The controversy surrounding soy largely stems from studies that focus on very high doses of soy isoflavones, far beyond what the average person consumes. For example, an individual must consistently consume moderate amounts of 40 to 70 mg of isoflavones daily to achieve a health impact as phytoestrogens from food are not easily absorbed. For reference, one cup of soy milk contains about 28 mg of soy isoflavones. The average consumption of isoflavones in a traditional Asian diet is 15 to 50 mg per day and only 2 mg per day in a Western diet.
Soybeans are an excellent source of protein, particularly for those who consume a plant-based diet. Some science-backed health benefits of soy phytoestrogens include bone health, heart health and cancer prevention. Research indicates that phytoestrogens may support cardiovascular health by improving cholesterol levels and reducing blood pressure. The potential for phytoestrogens to reduce the risk of osteoporosis by promoting bone health is also promising, especially in postmenopausal women, who are at increased risk of bone loss due to lower estrogen levels.
Phytoestrogens can exert a mild estrogenic effect, which may help alleviate symptoms like hot flashes and night sweats in menopause. Conversely, in individuals with high levels of estrogen, such as premenopausal women, phytoestrogens may block excess estrogen from binding to receptors, potentially offering protective benefits against estrogen-driven conditions like breast cancer.
For men, phytoestrogens may have protective effects on prostate health. Some studies suggest that consuming soy may reduce the risk of prostate cancer by interfering with the growth of cancer cells. However, the evidence is still mixed and more research is needed.
For children, the concern primarily revolves around the potential impact on sexual development. Some research has raised concerns about the consumption of large quantities of phytoestrogens in children, as it may interfere with their hormonal development. However, these effects are mostly theoretical, and current evidence does not indicate significant harm when phytoestrogen intake is moderate.
To benefit from the science-based health benefits of soy foods while minimizing any potential risks, there are a few important takeaways. First, moderation is key. Consuming one or two soy foods daily is well within a moderate level of soy intake. Second, pass on the soy protein powders and isoflavone supplements and opt for whole and minimally processed soy foods like edamame, tofu, tempeh and miso as part of a balanced diet. Finally, remember that everybody is different and some people may benefit more than others from the nutrition and health benefits of soy.
LeeAnn Weintraub, MPH, RD is a registered dietitian, providing nutrition counseling and consulting to individuals, families and organizations. She can be reached by email at RD@halfacup.com.