You Should Know

March 2015 Issue

Soy Myths Exposed

Plenty of myths surround soy, from causing breast cancer to feminizing men. But what does the science say? Since 1990, over 10,000 peer-reviewed studies have been conducted on soy, a food consumed worldwide in many forms over the centuries. The evidence indicates that moderate soy consumption is safe, and even healthful.

Photo: Thinkstock

Soy foods: tofu, tempeh, soymilk, soy sauce, and soybeans.

Myth #1: Soy contains estrogen.
The benefit of soy—and also a cause for criticism—is the phytochemical group called isoflavones. Phytochemicals, beneficial compounds in plants, have been studied for their role in disease prevention. Isoflavones have been called phytoestrogens (plant estrogens) because they bind to some estrogen receptors in the body, but their activity is not the same as estrogen; in fact, in some cases they have anti-estrogenic effects. Indeed, moderate soy consumption does not raise the risk for hormone-related cancers, such as breast cancer. While there is a published case study of hypogonadism (reduced testosterone) related to soy consumption, over 14 servings a day were being consumed in the study. Studies using up to six servings per day have not shown any impact on feminization or sperm quality or quantity in men.

Myth #2: Soy contains “anti-nutrients.”
Soy, like other wholesome plant foods, such as whole wheat and potatoes, contains phytates, which may reduce the absorption of some minerals. Theoretically this could be a concern, but in practice does not lead to any vitamin or mineral deficiencies in a balanced, healthy diet. The calcium in soymilk, for example, is absorbed at about the same rate as that of cow’s milk. Ferritin, the type of iron found in high amounts in soy, is absorbed particularly well. Firm tofu, made from soy, is an especially good source of iron. Adding a vitamin C-rich food, such as citrus or bell peppers, significantly increases iron absorption.

Myth #3: Only fermented soy foods are healthy.
Much of the evidence on soy health benefits comes from Asian populations with centuries of consumption—and lower risks of breast cancer and heart disease compared to the U.S. Some critics argue that soy is merely a condiment in Asian cultures, or that only fermented soy is eaten, but this is not the case. In Japan, fermented soy, such as natto and miso, are consumed regularly, but so is tofu. Most of the soy consumed in China is not fermented, and in Indonesia, where tempeh (fermented soy and grain cake) is a common food, non-fermented types of soy also are eaten. The total amount of phytochemicals in fermented versus non-fermented soy varies little.

The benefits and versatility of soy far outweigh health concerns. Focus on whole soy foods, like tempeh, tofu and soymilk, over more processed versions such as soy protein isolate and “fake meats.”