Edamame, tofu, tempeh, miso, and soy milk… are soy foods healthful or harmful?
Soy foods contain impressive amounts of high quality plant proteins and fibers. For example, one half cup serving of edamame (young green soybeans) contains 13 grams of protein and 12 grams (48% DV) of fiber.
Soy foods also contain an array of phytochemicals (plant chemicals) that are thought to affect human health such as isoflavones (genistein and daidzein), saponins, phenolic acid, phytic acid, protease inhibitors, and sphingolipids. These phytochemicals may act as antioxidants, lower cholesterol, initiate the self-destruction of abnormal (potentially cancerous) cells, and stop cancer cells from spreading.
Some concern has arisen over the isoflavones in soy foods because they may act as very weak forms of estrogen. However, they also have anti-estrogen properties and may block more potent forms of natural estrogen from binding to estrogen receptors.
The American Institute for Cancer Research/ World Cancer Research Fund continuous report on diet and cancer indicates that soy foods either have no effect on cancer risk or may slightly lower the risk for breast and prostate cancer.
“The human evidence, clinical and epidemiologic, overwhelmingly shows isoflavone exposure is not harmful for and may even benefit breast cancer patients. For breast cancer risk among cancer-free women, studies on soy consumption either show no link or a slightly protective link to breast cancer. Some research suggests that protective effects may primarily come from consuming soy during childhood and adolescence. ” (1)
Current research suggests that moderate amounts of soy foods (e.g., 1-3 servings per day) can be a healthful addition to the diet. One serving equals 1/2 cup of edamame, 3 ounces of tofu or tempeh, or 1 cup of soy milk.
Be careful not to confuse soy foods with isolated soy isoflavones in supplement form. Research has not demonstrated their safety or effectiveness.
Learn more about soy foods here:
AICR: Foods That Fight Cancer (Soy)
CSPI: Is Soy Linked to Breast Cancer?