Soy is one of the most significant sources of isoflavones in our diet. Isoflavones are phytoestrogens (plant estrogens) that belong to a family of phytochemicals called polyphenols. Many of the health benefits of soy (other than its macro and micronutrient contributions), are due to these plant estrogens. The plant estrogens seem to have a positive effect on postmenopausal women by enhancing heart health and brain function. .
However, these plant estrogens have garnered much controversy. A commonly held belief is that isoflavones are beneficial for those who need estrogen (e.g. menopausal women), but detrimental for those who don’t (e.g. women with certain types of breast cancer and men who believe they can be “feminized” by estrogen).
This is not entirely true because isoflavones are not the same as human estrogen.
Isoflavones only have weak estrogenic effects in postmenopausal women. On the other hand, isoflavones appear to act as an anti-estrogen where breast cancer risk is concerned. That’s good news.
To sum up, while the effects of soy tend to be favorable for women, men are frequently concerned that soy may reduce testosterone levels, and generally cause a feminizing effect. Only two case studies have appeared in the literature regarding feminization of men ingesting soy.
In both cases, the men regularly consumed 14 to 20 servings of soy daily – one derived almost all of his calories from soy – and subsequently developed health problems, such as enlarged breast tissue and loss of libido. In both cases, when soy intake was reduced, their health and libido returned to normal.
There are many health benefits associated with consuming soy. For example, soy has been shown to
lower your risk of cardiovascular disease,
protect against some types of cancer
balance hormones to reduce hot flashes, and
protect against osteoporosis.
Cardiovascular disease (CVD) – Scientific studies suggest that soy foods reduce your risk of heart attacks. A 2011 study estimated that an average intake of 30 grams of soy protein per day was associated with a reduction in LDL cholesterol (the bad kind) of about 5%. Soy intake also increased HDL cholesterol (the good kind) levels and reduced triglycerides.
Scientific research also suggests that soy consumption reduces the thickness of coronary arteries; when your arteries are thicker, CVD risk is elevated.
Reduced Risk of Breast and Prostate Cancer – Scientific studies further suggest that soy intake reduces risk of prostate and breast cancer.
Prostate Cancer. Asian men who consume about two servings of soy foods per day are about 30 -50% less likely to develop prostate cancer than Asian men who do not consume soy. Further, prostate cancer is significantly lower in Asian populations, compared to North American or European populations. But when Asian men relocate to America and adopt Western diets, they quickly assume the same risk for contracting prostate cancer as others who eat the rich Western diet.
Breast Cancer. For years, doctors warned breast cancer patients to avoid soy products due to concerns that soy phytoestrogens would act like human estrogen and increase cancer cell growth. However, recent studies suggests that isoflavones act more as anti-estrogens than human estrogen in reproductive cells (e.g. breast and uterus tissue), improving breast cancer prognosis. Furthermore, many studies have supported the benefits of soy in reducing risk of breast cancer and to highlight just one, a recent study reported those subjects who with the BRCA1 and BRCA2 genes (genes that increase breast cancer risk) who measured in the top 25% of soy intake in the group were associated with a 61% reduced risk of breast cancer; while subjects with the same gene who measured in the top 25% of meat intake had almost double the risk of breast cancer.
Balancing Hormones/Reduction in Hot Flashes – It has long been suspected that soy reduces hot flashes in women and while the evidence is not overwhelming, based on 2012 studies, the study suggests that soy, in the form of isoflavone supplements, reduces hot flash frequency by 21% and their severity by 26%. To date, the evidence is stronger for isoflavone supplements over soy foods for the greatest benefit.
Possible Protection Against Osteoporosis – There is some scientific evidence that consumption of soy foods is protective against bone fractures. In one study scientists reported a 5.8% improvement of bone mineral density in postmenopausal osteopenic women who were given 54 mg genistein per day (about four servings of soy), compared to a 6.3% decrease of bone mineral density in the placebo group.
Soy products can contribute nutritional health at any age.
Soy foods fall into two categories: fermented (e.g. tempeh, miso and natto) and non-fermented (e. g. tofu, soymilk, edamame soybeans and soy nuts). Despite their health benefits, sometimes soy gets a bad wrap. And here’s why:
Soy contains two anti-nutrients that are common among legume family: phytates and lectins. Phytates can interfere with the absorption of certain minerals and lectins can bind to the lining of your intestines and cause intestinal wall damage, but the negative effects of these anti-nutrients can be largely eliminated through the process of soaking, fermenting or cooking.
These preparation methods for both non-fermented products – such as soy milk and tofu –and fermented soy products such as tempeh, not only reduce anti-nutrients but also improve digestibility and mineral absorption.
But the fermentation process has an additional benefit too; it helps to support beneficial gut flora. That is, it helps populate the gut with beneficial bacteria that assist with everything from your immune system to mental health.
On the other hand, highly processed soy products, like veggie meats, sausages, deli slices and protein powders and bars, are sometimes made from a concentrated form of soy protein called “soy protein isolate” that is not easily digested and many times can be contaminated with hexane, a toxic solvent which is used to extract the protein from the soy. You can avoid soy protein that has been processed using hexane by purchasing certified organic products, but I would keep these soy products to a minimum.
Some of the soy cheeses contain partially-hydrogenated oils (trans fats) and trans fats should always be avoided.
See my post on Soy and Your Hormones for more information about how soy can affect your hormones.
For many years, soy has been a staple of Asian diets. One of the healthiest, long-lived populations in the world – the Okinawan Japanese — consume soy daily. In fact, a typical Okinawan receives about 5-6% of total calories from soy each day. That’s about 2 servings/day. If soy was unhealthy, these populations would not be outliving the rest of us.
Second, soy has been extensively researched by reputable scientists. In fact, roughly 2,000 new studies on soy are released every year indicating benefits as broad as lowering risk of breast cancer to heart disease. To maximize these healthful benefits, the best ways to consume soy are in their least processed form as whole beans like “edamame” or fermented soy like “tempeh” and, as with anything, in moderation.
Over the past several years, many groups promoting animal-based diets have done an impressive job of convincing consumers to avoid soy, but their reasons are not based in science. Many of these groups are financially invested in meat,dairy and egg industries and fear the competition from soy milk and soy-based “meat” products. .
There are some legitimate concerns about soy, though, especially if you have problems with your thyroid as it can interfere with iodine absorption and some individuals may be allergic. Another concern is overuse of soy, particularly in the highly processed forms. However, for most people, soy foods are safe and full of valuable nutrients. So enjoy! And please read and share my upcoming post “The Most Healthful Soy Foods” for more on soy.