It’s hard to visit a supermarket without finding soybeans, soy milk, soy cheese, and the entire spectrum of soy products. However, there are several controversies concerning soy and its safety. What are these controversies? Should you avoid soy – or enjoy it?
Soy products contain Isoflavones — Polyphenolic compounds that possess both estrogen-agonist and estrogen-antagonist properties. That's why they are classified as phytoestrogens (plant-derived compounds with estrogenic activity).
Phytoestrogens hinder the body's natural estrogen from attaching to cells. Normally, estrogens hook onto tiny receptor proteins in your cells that allow them to change the cell's chemistry. When phytoestrogens occupy the cell, normal estrogens cannot. Plant estrogens do not eliminate all of estrogen's effects, but they do minimize them.
Soy & Health
Scientists are interested in the tissue-selective activities of phytoestrogens because anti-estrogenic effects in reproductive tissue could help reduce the risk of hormone-associated cancers (breast, uterine, and prostate), while estrogenic effects in other tissues could help maintain bone mineral density and improve blood lipid profiles. The extent to which soy isoflavones exert estrogenic and anti-estrogenic effects in humans is currently the focus of considerable scientific research.
Soy & Cancer
Soy products have been shown to reduce estrogen activity, at least in premenopausal women, which, over the long run, reduces cancer risk.
High isoflavone intake from soy foods in Asian countries (average range, 25 to 50 mg/day) has been suggested to contribute to reducing the risk of breast cancer.
There is little evidence from intervention trials to suggest that taking soy isoflavone supplements could decrease the risk of endometrial (uterine) cancer.
Soy & Male Reproductive Health
Claims that soy food/isoflavone consumption can have adverse effects on male reproductive function, including feminization, erectile dysfunction, and infertility, are primarily based on animal studies and case reports.
Exposure to isoflavones (including at levels above typical Asian dietary intakes) has not been shown to affect either the concentrations of estrogen and testosterone, or the quality of sperm and semen.
Phytoestrogens in soy do not appear to have any effect on hormone levels in men and have not been shown to affect sexual development or fertility.
Research studies show that men consuming soy have less prostate cancer and better prostate cancer survival.
Soy & Cardiovascular Health
Soy is actually good for your heart. One study suggests that eating foods that contain isoflavones (like soy products) every day may help young adults lower their blood pressure, particularly African-Americans. It is thought that the isoflavones work by encouraging your body to produce nitric oxide, which helps to dilate blood vessels and reduce the pressure created by blood against the vessel walls.
Whole soy foods contain high levels of healthy protein and fiber. Fiber helps to reduce bad cholesterol. Plus, soy is a much better source of protein for your heart than saturated-fat-rich animal-derived foods.
Two recent meta-analyses of randomized controlled trials indicated that isoflavones might exert cardiovascular benefits by improving vascular function in postmenopausal women.
Soy & Osteoporosis
The decline in estrogen production that accompanies menopause places middle-aged women at risk of osteopenia and osteoporosis. The measurement of bone mineral density (BMD) loss by dual-energy X-ray absorptiometry is generally used in the diagnosis of osteoporosis.
Compared to Caucasian women, the incidence of hip fractures tend to be lower among Asian women who are habitual soy food consumers, suggesting that long-term soy food consumption might protect against bone loss or osteoporotic fracture. Moreover, pooled analyses combining intervention trials in Caucasian and Asian postmenopausal women reported significant increases in BMD with supplemental soy isoflavones.
Soy & Thyroid Function
The available research suggests that soy may not affect thyroid function, especially in those who have a normal thyroid.
However, soy may be dangerous for those who already have an existing thyroid problem and take medications for their thyroid. This is because soy products may interfere with how the body absorbs the medication in the GI tract, making it less effective. A general tip for those taking thyroid medication would be to wait a few hours between taking your thyroid medication and consuming any soy products as soy tends to alter how your intestines absorb the medication. Talk to your physician about soy and any thyroid medications you may be taking.
Soy Infant Formulas
Soy protein-based infant formulas are made from soy protein isolate and contain significant amounts of soy isoflavones.
The American Academy of Pediatrics (AAP) supports the use of soy protein isolate-based formula for normal growth and development of term infants whose needs are not being met by human milk or cow’s milk-based formulas. Soy protein-based formulas are especially indicated for infants with galactosemia and hereditary lactase deficiency.
Since infants fed soy-based formulas are exposed to relatively high levels of isoflavones, which they can absorb and metabolize, concern has been raised regarding potential long-term effects on anthropometric growth, bone health, as well as reproductive, endocrine, and immune functions. In addition to the AAP review, a recent systematic review and meta-analysis of data published between 1909 and 2013 found no clinical concerns regarding nutritional adequacy, sexual development, thyroid disease, immune function, and neurodevelopment in infants fed soy protein-fed formulas.
Soy isoflavones have been consumed by humans as part of soy-based diets for many years without any evidence of adverse effects. Although diets rich in soy or soy-containing products appear safe and potentially beneficial, the long-term safety of very high supplemental doses of soy isoflavones is not yet known.
Like all foods, you want to consume soy in moderation. One to two servings of whole and fermented soy foods is recommended. One average serving is a half-cup of tofu or 1 cup of soy milk.
But not all soy products are created equal. Thanks to savvy marketing and nutritional buzzwords, most of us think we are automatically doing a good thing for ourselves when we choose soy foods. Unfortunately, this isn’t always true. Make the right selections to ensure you’re getting the best and purest forms of nutrition from soy foods and soy products.
Genetically Modified Soybeans
Non-GMO soybeans have traditionally been used to make soyfood products such as tofu, miso, and soymilk, while GM soybeans have been used for animal feed or processed into oil and soybean meal. But with higher food prices worldwide and fewer non-GMO soybean varieties available, more food manufacturers in Asia and even the United States are using GM soybeans to make soyfoods.
While GMO foods themselves cannot be classified as unhealthy, other related factors may cause adverse effects. The herbicide glyphosate, which is sprayed on some GMO crops, may be harmful to health.
Some research links GMOs to allergies, organ toxicity, and other health issues, though the U.S. Food and Drug Administration does not require safety testing for GMOs.
It’s also to remember that a vegan diet of beans, vegetables, grains, and fruits does not have to include soy products to be nutritionally complete. Soy products make convenient and tasty substitutes for meat and other unhealthy foods that people, quite rightly, are looking to avoid.