Soy Health Benefits: Myth v. Fact
Myths about the health risks of soy persist, despite the evidence that this protein-packed superfood has sustained robust populations in Asia for thousands of years.
Soy protein is considered nutritionally complete, meaning it contains all of the essential amino acids in sufficient quantities to help meet the human body's requirements.
Soy foods are considered a smart choice for a heart-healthy lifestyle. They are generally lower in saturated fat and cholesterol than their animal-based counterparts. More than 80 studies over the past 40 years have shown that soy protein directly lowers LDL ("bad" ) cholesterol. Soy also contains naturally occurring ALA omega-3 fatty acids, which have been studied for their role in heart health.
And a number of research studies suggest that soy consumption is associated with a decreased risk of prostate cancer in men and breast cancer in women.
Yet many people have turned away from soy foods in the mistaken belief that they contain the hormone estrogen which "feeds" tumors, heightens the risk of breast cancer and create a range of developmental problems for prepubescent children.
Here are some common misperceptions, and the true "soy stories" behind the myths.
Myth: Soy increases cancer risk.
Fact: In fact, a number of scientific studies suggest a link between soy consumption and reduced risk of certain cancers, including breast and prostate cancer.
Myth: Soy contains the hormone estrogen.
Fact: Soy does not contain the hormone estrogen. It does, however, contain isoflavones, also known as phytoestrogens or "plant estrogens." While the chemical structure of isoflavones is similar to estrogen, the two function very differently in the body. Isoflavones have been studied for a number of beneficial effects including a potential role in supporting heart and bone health, minimizing menopausal symptoms and reducing the risk of some forms of cancer.
Myth: Women should avoid soy.
Fact: In fact, research suggests that soy may have specific benefits in the areas of menopause, osteoporosis, and breast cancer. Many of these studies are based on women in Asia, whose diets are rich in soy protein.
Asian women living in Asia enjoy significantly lower breast cancer risks than women in the West. "Living in Asia" is the key phrase here, because when they move to the West, Asian women lose their low-cancer advantage a phenomenon widely attributed to the Westernization of their diet and lifestyle.
Myth: Consuming soy causes feminizing effects in men.
Fact: Claims that soy exerts feminizing or estrogenic effects in men are not supported by science. Clinical studies show conclusively that neither soy foods nor isoflavones affect testosterone or estrogen levels or sperm quality or quantity.
Myth: Consuming soy affects children's sexual development.
Fact: There is no scientific evidence showing that soy affects children's sexual development.
Myth: All soy food is the same.
Fact: Definitely not true. "Whole" soy foods such as tofu, edamame, and soy milk made from whole soybeans often preserve more natural soy nutrition than do processed products made from isolated soy protein (often listed in ingredients as soy protein isolate).
Some nutrition experts believe this may be the key to the soy health controversy. We know that Asian cultures have consumed soy foods for thousands of years and that these populations are generally healthier when compared to Westerners. But unlike our Asian counterparts who generally consume their soy in the form of whole foods, we in the West consume a lot of soy protein isolate.
Isolated soy protein is a processed food made from dehulled defatted soybean meal, and is used extensively by the food industry. Tofu hot dogs, veggie burgers, soy chips, and cereals and bars ... not to mention many other products marketed as "high protein" foods, often contain high amounts of this form of protein.
While we know that consumption of whole soy foods have benefited humans for generations, when it comes to "technologically manipulated" soy products, we know nothing about their long-term risks and benefits.
How much soy is enough? How much is too much?
There is no Recommended Daily Allowance for soy protein. Many studies show positive impact from as little as 10 to 15 grams per day. This amount of soy protein can be found in 1 to 2 servings of most soy foods.
With the exception of allergic reactions (relatively rare among adults), there is no evidence that soy protein leads to undesirable effects in healthy individuals, regardless of the amount consumed. Nevertheless, the dietary principles of moderation and variation should apply: No single food should play too large of a role in the diet; nutrients should come from a variety of different foods.