From the Guidelines
Consuming moderate amounts of soy is generally considered safe for most people, despite concerns about its phytoestrogen content. Soy contains isoflavones, which are plant compounds that can weakly mimic estrogen in the body but are much less potent than human estrogen. For most adults, consuming 1-2 servings of soy foods daily (such as 1/2 cup of tofu, 1 cup of soy milk, or 1/2 cup of edamame) is unlikely to cause hormonal disruptions 1. The concerns about soy's estrogenic effects have been largely overstated based on current research. In fact, population studies in Asian countries where soy consumption is high show no increased rates of hormone-related conditions.
Some key points to consider when consuming soy include:
- Moderate intake is recommended, with up to three servings per day of soy foods such as tofu and soy milk 1
- Avoiding high doses of soy and soy isoflavones from concentrated sources such as soy powders and isoflavone supplements is prudent, especially for breast cancer survivors 1
- Whole soy foods like tofu, tempeh, and edamame are healthier choices than highly processed soy protein isolates found in many supplements and processed foods
- Some individuals may wish to moderate their intake, including those with specific thyroid conditions (as soy can interfere with thyroid medication absorption) or hormone-sensitive cancers (though recent research suggests soy may actually be protective) 1.
Overall, the benefits of moderate soy consumption, including its potential to reduce the risk of cardiovascular disease and certain cancers, outweigh the risks for most people 1.
From the Research
Soy Consumption and Estrogen Levels
- Soy contains isoflavones, which are phytoestrogens with a similarity in structure to human 17-β estradiol hormone, and can imitate the action of estrogen on organs by binding and activating estrogen receptors 2.
- The role of soy isoflavones in cancer prevention and promotion is somewhat unclear, with two views suggesting that soy and its isoflavones have exhibited cancer-preventive properties, while others speculate that isoflavones may behave as weak estrogens 3.
- However, current human and animal data provide evidence for several anticancer properties of soy and/or its isoflavones, and it appears that soy isoflavones do not function as an estrogen, but rather exhibit anti-estrogenic properties 3.
Recommended Soy Intake
- Health professionals and consumers are seeking guidance regarding appropriate soy intake levels, with a recommended intake of 15 g (range 10-25 g) soy protein and 50 mg isoflavones (range 30-100 mg)/day for healthy adults 4.
- Increasing dietary whole soy protein has been shown to lower levels of total cholesterol, low-density lipoproteins, and triglycerides, and may improve menopausal hot flashes and help maintain bone density and decrease fractures in postmenopausal women 5.
Soy and Breast Cancer Risk
- A meta-analysis found a clear inverse correlation between the amount of isoflavones consumed and breast cancer occurrence in pre- and post-menopausal women, suggesting that soy isoflavones can reduce the risk of breast cancer 2.
- Epidemiological and migratory evidence also suggests that dietary soy consumption can lower the risk for breast cancer, with soy and its isoflavones exhibiting cancer-preventive properties 3.