The Soy Controversy
Given the fact that soybeans are a food that has been enjoyed by millions of people over thousands of year, it’s unexpected to find so much controversy surrounding this legume. And yet in the public press and in scientific research, soybeans have been a topic of ongoing controversy. For example, in 1999, the U.S. Food and Drug Administration (FDA) authorized a health claim for soy protein as a nutrient that could reduce risk of heart disease. And yet in 2007, numerous scientists in the U.S. officially asked the FDA to revoke its heart-related health claim for soy protein.
We suspect that one basic factor accounts for most of the controversy that has surrounded soy and its role in a healthy diet. This factor is what we would summarize as “east versus west.” Soybeans were adopted as important parts of the diet in China (and then later in Japan and Korea) long before they became part of European or North American diets. Culinary traditions involving soy have existed for dozens of generations across Asia, but remain almost non-existent even today in Western countries like the United States. When research is conducted on the health benefits of soybean in Asian diets, the findings seldom match up with research findings on U.S. and European populations.
What makes Eastern countries and Western countries so different with respect to soy? The answer to this question is complicated, but three issues seem especially important.
Soybeans are typically consumed as whole foods in the East
First and perhaps foremost is the approach to soybeans as a dietary component in Eastern versus Western countries. In Eastern countries like China, Japan, and Korea, soybeans are typically consumed as whole foods. They may be cooked, roasted, fermented, or sprouted, but they are allowed to remain intact in the diet. Soybean consumption in Asia almost always involves a form of the legume that is whole food-related. In sharp contrast, consumption of soy in the United States seldom involves a whole food form. In the U.S., most of the soybean we consume has been highly processed, following cracking, dehulling, crushing, or being subjected to solvent extraction processes to separate the oils from the rest of the bean.
Total soy consumption is different when comparing East to West
The amount of total soybean consumption in Eastern versus Western countries is also very different. In studies from China and Japan, it’s not surprising to see intake of soybeans occurring at the level of 100-200 grams per day. Yet in the U.S., we average less than one-tenth of that amount.
Longstanding culinary traditions involving soy also seem to have contributed in various ways to important metabolic differences in Asian versus non-Asian populations. For example, about 50-60% of adults in Japan, China and Korea digest soybeans in such a way as to convert daidzein (one of soy’s key isoflavone phytonutrients) into equol (a closely-related phytonutrient called an isoflavan). By contrast, when U.S. adults eat soybeans, only 25-30% metabolize daidzein in this way. The role of bacteria in the digestive tract seems critical in the equol production process, and there may be other aspects of metabolism that also play pivotal roles.
When combined, these metabolic and whole-versus-processed food differences make research on soy difficult to interpret. A soy-related dietary practice that works for adults in China may not work for adults in the U.S., or vice-versa. In addition, until soybeans are enjoyed on a more regular basis in their whole food form in the U.S., research studies on U.S. adults may continue to show mixed results in terms of health benefits.
Even with all of the “east versus west” circumstances that complicate research on soybeans and health, we believe several areas of health benefit still shine through in studies of this much-loved legume. In the paragraphs below, you will learn more about these specific health areas.
GI: very low
Overall Nutrient Benefits
According to a recent research analysis, U.S. adults would increase their intake of folate, vitamin K, calcium, magnesium, iron and fiber if they replaced their meat and dairy intake with soy. Since legumes like soybeans are often overshadowed by vegetables and fruits in terms of nutrient richness, we sometimes forget just how beneficial legumes like soybeans can be.
Along with the nutrients listed above, soybeans are also an important source of the minerals copper, manganese, molybdenum, phosphorus, and potassium; the B vitamin, riboflavin; and omega-3 fatty acids (in the form of alpha-linolenic acid). Replacing meat and dairy with soy would also lower total cholesterol intake by about 125 milligrams per day and saturated fat by about 2.4 grams per day. These nutritional changes, in turn, would lower risk of several chronic diseases, including cardiovascular diseases. The idea of getting 10 grams of fiber and 25-30 grams of high-quality protein for 300 calories (1 cup of soybeans) is somewhat amazing. On a diet of 1,800 calories, 300 calories would only represent 16-17% of the total calories for one day. Yet, while only taking up one-sixth of the day’s calories, a cup of soybeans provides us with 40% of the Daily Value for fiber and 50-60% of the Daily Value for protein!
In addition to all of their nutrient richness described above, soybeans also offer many unique nutrients less familiar to most people. In some cases, the health benefits of these nutrients are only beginning to be understood by researchers. Below is a list of some key nutrients currently under investigation in soybeans.
- Flavonoids and Isoflavonoids
- Phenolic Acids
- Caffeic acid
- Coumaric acid
- Ferulic acid
- Gallic acid
- Sinapic acid
- glyceollin I
- glyceollin II
- glyceollin III
- Proteins and Peptides
- soyasaponins (group A and group B)
As discussed earlier, research on soybeans has provided mixed results in the area of cardiovascular benefits, with some studies showing no benefits and other studies showing significant ones. We believe that two aspects of the “east versus west” phenomenon described earlier may have contributed to these mixed findings. First is the difference between studies involving whole soybeans versus studies involving processed soybean components (like soy protein isolates). In repeated research findings, whole food soybeans have been shown to provide us with better cardiovascular support than dietary supplements containing soy components. “Better” in this case means not only more consistent but also more in-depth cardiovascular support.
However, even in the case of whole food soybeans, we would not describe this cardiovascular support as being “strong.” A better word would be “moderate.” The most consistent effect of soybean intake on blood fats has been a moderate lowering of LDL cholesterol. Some studies show other positive impacts on blood fats, such as the lowering of triglycerides and total cholesterol or the raising of HDL cholesterol (the “good” cholesterol). However, these additional blood fat results have not been confirmed in all studies.
Soyasaponins are soy phytonutrients that have been especially interesting to researchers with respect to their cardiovascular benefits. There is some evidence, mostly in animal studies, that soyasaponins can lessen the rate of lipid peroxidation in blood vessels, lessen absorption of cholesterol from the GI tract, and increase excretion of fecal bile acids. All of these events would be expected to contribute to a decreased risk of cardiovascular disease. We look forward to further studies involving humans who take in soyasaponins through a normal diet that includes whole food soybeans.
Cancer Prevention Benefits
The area of cancer prevention is perhaps the most controversial area of health research on soybeans. Many studies provide us with evidence that supports the role of whole soy foods in a cancer-preventing diet. Genistein (an isoflavone phytonutrient in soy) is often a key focus in these cancer-prevention studies. This soy isoflavone can increase activity of a tumor suppressor protein called p53. When p53 becomes more active, it can help trigger programmed cell death (apoptosis) in cancer cells, and it also help trigger cell cycle arrest (helping stop ongoing cancer cell activity). Genistein has also been shown to block the activity of protein kinases in a way that can help slow tumor formation, especially in the case of breast and prostate cancer. It’s also worth noting here that genistein becomes more concentrated in soy foods when those foods are fermented.
All of the above cancer-preventing possibilities of genistein and soy are complicated by other real-life factors, however. In some studies, the amount of genistein required to trigger cancer-preventive effects has been relatively high, and far higher than the amount provided by average intake among U.S. adults. The lifecycle and metabolic status of individuals also seems to make a potentially important difference in the anticancer benefits of soy. For example, in studies on soy intake and breast cancer, women who are pre-menopausal and develop tumors that are neither estrogen receptor nor progesterone receptor positive, soy and genistein intake do not appear to offer risk reduction. Overall dietary intake may also make an important difference in the anticancer benefits of soy. For example, without strong dietary intake of fresh fruits and vegetables, soy foods many not provide a reliable level of anticancer benefits.
In addition to the precautions about anticancer benefits of soy described above, there is also some evidence that large amounts of processed soy components (like might be obtained from large doses of purified soy isoflavones through dietary supplements) may actually increase risk of certain cancers, including breast cancer. This evidence should not be surprising. Under certain metabolic circumstances, most antioxidant, anti-inflammatory, and anti-tumor compounds can also act in a way that is pro-oxidant, pro-inflammatory, and pro-tumor (often called a “proliferative” affect that is promoting of tumor growth). It’s certainly easy to see why soy has remained so controversial in the minds of some researchers!
Our recommendations to you based on all of this information are as follows: first, if you have a family history of hormone-related cancers like breast cancer or prostate cancer, we recommend that you consult with your healthcare provider before consuming very large amounts of soy in your diet (for example, 3 or more servings per day). This recommendation is a conservative one on our part, but we believe that it’s justified based on the current level of controversy in the health research. Second, we recommend that you choose whole food soybeans whenever possible, rather than highly processed versions like soy protein isolates and soy protein concentrates. Finally, we recommend that you consider fermented versions of soy (including tempeh, fermented tofu, and miso) which have a better research track record in the cancer prevention area than non-fermented soy products.
In the overall picture, we continue to believe that soy foods can provide you with important health benefits, including anti-cancer benefits. But we also believe that persons wanting to include soy in an anti-cancer diet need to pay attention to the form of the soy, the amount consumed, their personal health history, and in some cases, the advice of their healthcare provider.
Soy and Hot Flashes
Hot flashes are very common symptoms of menopause and peri-menopause in U.S. women (often called “night sweats” when they occur at night) can cause great suffering and can easily affect mood throughout the day and impair concentration. Approximately 70-80% of U.S. women of menopausal and peri-menopausal age experience hot flashes, in comparison with approximately 10-20% of Asian women. By comparison, the average level of the soy isoflavone genistein in the bloodstream of Asian women is approximately 25 nanograms per milliliter, but in U.S. women, only 2 nanograms. This sharp contrast between frequency of hot flash symptoms and soy genistein levels has led many researchers to wonder about the hot flash-preventing potential of soybeans. Unfortunately, most studies to date fail to establish a reliable connection between dietary soy intake and occurrence of hot flashes. It’s possible that future research studies will tell a different story, but at present, we aren’t aware of any findings that show clear benefits for hot flash relief from increased intake of soy.
Bone Health Benefits
The area of bone health benefits from soy has remained nearly as controversial as the anti-cancer area due to the large amount of mixed evidence found in human studies on soy and bone health. In support of bone benefits has been the finding in many studies of improved markers of bone health following consumption of soy. (Improved bone health markers have included a decrease in the number of cross-linked telopeptides and a decrease in blood levels of bone specific alkaline phosphatase.) In addition, a lower rate of osteoporosis in some countries has been associated with increased intake of whole soy foods, especially fermented whole soybean foods. At the same time, however, soy intake (especially processed soy intake, including soy protein concentrates, isolated soy protein, and supplements containing purified soy isoflavones) has often failed to show any improvement in bone mineral density or bone metabolism.
Some of the mixed findings appear to be related to conversion of the soy isoflavone, daidzein, by intestinal bacteria into a metabolite called equol. In some Asian countries, the rate of equol formation in adults is approximately double the rate of U.S. adults. (Interestingly, among U.S. adults, the rate of equol formation from daidzein is almost double in vegetarians versus non-vegetarians.) Soy foods appear to be more helpful in supporting bone (for example, in lessening loss of minerals from bone) when individual metabolism and gut micro-organisms support the conversion of daidzein into equol. There is also some evidence that this entire process may be under some level of genetic regulation.
In the overall picture, we continue to believe that soy foods can provide you with important health benefits, including bone-related benefits. It’s important to remember that soybeans provide a good amount of vitamin K—a much-needed nutrient with respect to bone health. (Soy foods fermented with Bacillus bacteria may be able to provide additional vitamin K benefits, as described later on in this Health Benefits section.) Equally important, soy protein is a plant protein. In broad studies of diet and bone health, plant proteins have a better track record in support of bone than animal proteins. Even though many controversies remain in the area of soybeans and bone health, we believe that your 4-8 cups of legumes each week (our World’s Healthiest Foods recommended intake level for legumes) should contain some whole food form of soybeans—and especially versions that have also been fermented.
Soybeans and Obesity
Increased protein intake has always been associated with suppression of appetite, and plant foods like soy that provide concentrated amounts of protein have a research-based ability to help suppress appetite. (Of course, our experience of appetite is very complicated, and there is no simple way to change our appetite exclusively through diet.) Some studies on unique peptides (protein-like components) in soy have shown the ability of this peptides to decrease synthesis of SREBPs (sterol regulatory element binding proteins), thereby helping decrease synthesis of certain fatty acids as well as depositing of these fatty acids in fat cells. This fascinating research on soyfoods and obesity is still in the early stages, however.
Soybeans and Type 2 Diabetes
A second area of potential health benefit is prevention of type 2 diabetes. In multiple animal studies, soy foods have been shown to lessen insulin resistance by increasing the synthesis of insulin receptors. However, this increased formation of insulin receptors only appears to occur in the presence of other dietary circumstances, like a moderate amount of polyunsaturated fat intake. High levels of total soy intake (approximately 200 grams per day) have also been associated with decreased risk of type 2 diabetes, but only in Asian populations thus far. We look forward to more research on human consumption of soy and prevention of chronic health problems related to insulin metabolism and blood sugar levels.
Soybeans and Vitamin K
Soybeans of all kinds qualify as a good source of vitamin K based on our food-nutrient ranking system. However, your vitamin K benefits from soybeans may be increased in the case of certain fermented soy foods. By far the most famous micro-organism used in fermentation of soybeans is the koji mold, Aspergillus oryzae. (Aspergillus oryzae can also be called a fungus, since molds are simply a special type of fungus called filamentous fungus.) Koji mold is a key to many of the unique qualities of many soy pastes, as well as soy miso and soy sauce. However, other micro-organisms may also be used to help ferment soybeans, and one is the bacterium Bacillus subtilis. The use of Bacillus subtilis in soybean fermentation is especially important in production of the fermented soy food, natto (and (Bacillus subtilis var. natto is one special variant (strain) of Bacillus used in natto production.) Natto is a sticky and stringy form of soybeans in which you can still see the individual beans. It has a distinctly pungent aroma, and it has been widely enjoyed in Asia cuisines for several thousand years, and especially in Japanese cuisine. However, Bacillus bacteria are also sometimes used in the production of other fermented soy foods, including soy pastes (especially Chinese soy pastes) and soy miso. Korean-style soy sauce may also be fermented with the help of Bacillus bacteria.
From a health standpoint, one of the reasons that Bacillus bacteria are so interesting is their ability to create a form of vitamin K called menaquinone-7 (MK-7). Vitamin K (in all forms) is an important nutrient for bone health. Sufficient intake of vitamin K is associated with decreased risk of osteoporosis, since this vitamin is involved with maintenance of bone mineral density and also with shaping of bone structure (through gamma-carboxylation). In the case of MK-7 (the form of vitamin K produced by Bacillus bacteria, and a member of the vitamin K2 menaquinone family), we know that higher levels of MK-7 in the blood correspond to lower risk of hip fracture in older Japanese women, and that higher MK-7 levels correspond to increased intake of soy foods that have been fermented with Bacillus bacteria. One fascinating aspect of Bacillus-fermented soy foods is the potential ability of these bacteria to stay alive in our lower intestine after these foods are consumed. We’ve seen one study in which 1.6-20 million Bacillus bacteria (per gram of feces) were found to remain alive up to 6 days following consumption of natto. If Bacillus bacteria from fermented soy foods can remain alive in our digestive tract, they may keep providing us with vitamin K benefits many days after their consumption.
Another interesting piece of information about vitamin K and fermented soy foods involves regulation of health claims on food products in Japan. The Foods for Specified Health Uses, or FOSHU system does not currently allow for bone-related health claims for natto in the Japanese marketplace, even though this food is an approved FOSHU product recognized as containing MK-7. The reason for disallowed health claims is the lack of vitamin K deficiency in Japan, not lack of data to support a possible MK-7 benefit. (In other words, the Japanese population may already be taking good advantage of fermented soy foods and their potential vitamin K benefits!)
Other Areas of Potential Health Benefit
Other areas of active research on soy and health include chronic obstructive pulmonary disease (COPD), periodontal disease, and neurodegenerative disease.
While not the most widely cultivated of all beans (that distinction goes to Phaseolus vulgaris, also know as the “common bean”), soybeans are a traditional part of diets in China, Japan and Korea and are currently grown in countries across the world including Brazil, Argentina, India, Paraguay, Canada, and the United States. At present, the United States plants and produces more soybeans than any other country in the world—approximately 83 million metric tons grown on 75 million acres of land. However, nearly 99% of all soybeans grown in the U.S. are processed for production of soil meal (to be used in animal feed) and soy oil. In countries where soybeans are consumed in whole food form rather than undergoing processing into meal and oil, these legumes often serve as an important and relatively inexpensive source of protein.
Like their fellow legumes, soybeans are actually seeds of a plant. In the case of soybeans, the plant is Glycine max. (The soybeans we find in the grocery store have already been removed from the pod and dried out.) We’re accustomed to seeing dried soybeans in their light tan or pale yellow color, but mature dried soybeans can actually be found in a variety of different colors including black, brown, and blue. Fresh (undried) soybeans, however, are always green in color and when carefully cooked—either in the pod or after being removed from the pod—can turn an even richer and brighter shade of green. Although you will find some websites referring to green soybeans as “immature soybeans,” that term isn’t always accurate. Soybeans could be harvest at an immature stage, but many green soybeans available for purchase in the grocery store are mature when harvested—just not dried. Edamame (which means “stalk beans” or “branch beans” in Japanese) is a term that you will often see used to describe fresh green soybeans that may be available either individually or still inside the pod and may either be raw or already boiled or steamed. In all cases, the major difference is that edamame have not been dried. It’s worth noting that in recent research studies, edamame have been shown to contain a similar level of isoflavonoids as cooked soybeans that were prepared from dry form.
Other whole food forms of soy include full fat soy milk, tofu, natto, and miso. Processed forms of soy such soybean oil, defatted soy flour and soy protein concentrates such as TVP (texturized soy protein and SPI (soy protein isolate) abound. We always recommend whole food forms of soy (for more detail on these different forms of soy see WHFoods Recommendations above).
Soybeans have been cultivated in China for thousands of years, and they also became popular in other Asian countries (especially Japan and Korea) over a thousand years ago (as early as the third and fourth centuries AD). Thanks to their origins in Asia, we continue to use three Japanese words – “tofu” (itself from the Chinese word “doufu”), “natto,” and “edamame” (meaning “branch bean” or “stalk bean”) to refer to various forms of this wonderful legume.
Many countries in the world depend on soybeans and other legumes as key sources of dietary protein. However, for the past 30-35 years, soybeans have seldom been produced in the United States for the purpose of being consumed in whole food form by humans. Instead, a $20 billion industry has grown up around the cultivation of soybeans as an “oilseed” crop that can be traded alongside of other interchangeable commodities like rapeseed, sunflowerseed, and cottonseed. Even though the United States has become the world’s larger grower of soybeans (producing approximately 83 million metric tons of soybeans on 75 million acres of land), these soybeans are not being cultivated for human food use but for other purposes (their extractable oil and their processing into animal feed). This historical trend has given rise to a whole new classification of soybeans as an “oilseed crop” or “oilseed commodity.” When economists talk about soybeans that are intended to be consumed in whole food form by humans, they use the terms “vegetable soybeans” or “garden soybeans” or “edible soybeans” to describe this food.
This new interest in soybeans as an oilseed crop has also been accompanied by widespread genetic engineering of the legume. Nearly 90% of all soy products in the U.S. marketplace now come from soybeans that have been genetically engineered (GE), making them one of the world’s top foods in terms of genetic modification. Genetic engineering of soybeans began as early as 1998 with the introduction of soybeans into the marketplace that had been modified for better resistance to the commercial herbicide glufosinate ammonium. Since 1998, at least eight other GE patents have been granted for use on soybeans, most of them involving better resistance to pesticides and herbicides. If you are trying to avoid consumption of GE soy in your diet, your best bet is to purchase certified organic soybeans and soy products, since genetic engineering is not allowed under federal organic regulations.
How to Select and Store
Dried soybeans are generally available in prepackaged containers as well as bulk bins. Just as with any other food that you may purchase in the bulk section, make sure that the bins containing the soybeans are covered and that the store has a good product turnover so as to ensure its maximal freshness. Whether purchasing soybeans in bulk or in a packaged container, make sure that there is no evidence of moisture or insect damage, and that the beans are whole and not cracked.
Canned soybeans (dried beans that have been cooked for you by the manufacturer) can be found in many markets. Unlike canned vegetables, which can lose much of their nutritional value, there is typically less loss of nutrient richness with the canning of soybeans. Canning lowers vegetables’ nutritional value since they are best lightly cooked for a short period of time, while their canning process often requires a longer cooking time and/or higher cooking temperatures. By contrast, dried beans require a longer cooking time whether they are cooked by the manufacturer and then canned for your convenience, or whether you purchase them in dry form and cook at home yourself. Therefore, if enjoying canned beans is more convenient for you, by all means go ahead and enjoy them. We would suggest looking for those that do not contain extra salt or additives. (One concern about canned foods is the potential for the can to include a liner made from bisphenol A (BPA). To learn more about reducing your exposure to this compound, please read our write-up on the subject).
Of course, another alternative for soybeans is to purchase them in their fresh green form before they have been dried. Edamame (fresh green soybeans that may be raw or may already have been boiled or steamed either individually or in the pod) should be deep green in color and if purchased in the pod should come from pods that are firm and unbruised. Edamame can be found in many supermarkets as well as in natural foods stores and Asian markets. It is usually available in the frozen food section, although during its peak season you can find it the produce aisle of many natural food stores and Asian markets.
Remember to stick with the whole food forms of soy, and also consider giving preference to fermented versions like tempeh, fermented tofu, and soy miso.
Store dried soybeans in an airtight container in a cool, dry and dark place where they will keep for up to 12 months. If you purchase soybeans at different times, store them separately since they may feature varying stages of dryness and therefore will require different cooking times. Cooked soybeans will keep fresh in the refrigerator for about three days if placed in a covered container.
Fresh edamame should be stored in the refrigerator and eaten within two days. Frozen edamame will keep fresh for a few months.
Tips for Preparing and Cooking
Tips for Preparing Soybeans
Before washing dried soybeans, spread them out on a dark colored plate or cooking surface to check for and remove small stones, debris or damaged beans. After this process, place the beans in a strainer and rinse them thoroughly under cool running water.
To shorten their cooking time and make them easier to digest, dried soybeans should be presoaked. There are two basic methods for presoaking. For each, start by placing the beans in a saucepan and adding two to three cups of water per cup of beans.
The first method is to boil the beans for two minutes, take pan off the heat, cover and allow to stand for two hours. The alternative method is to simply soak the beans in water for eight hours or overnight, placing pan in the refrigerator so that the beans will not ferment. Before cooking the beans, regardless of method, drain the soaking liquid and rinse the beans with clean water.
The Healthiest Way of Cooking Soybeans
To cook soybeans, you can either cook them on the stovetop or use a pressure cooker. For the stovetop method, add three cups of fresh water or broth for each cup of dried beans. The liquid should be about one to two inches above the top of the beans. Bring the beans to a boil and then reduce to a simmer, partially covering the pot. If any foam develops, simply skim it off during the simmering process. Soybeans generally take about one to one and one-half hours to become tender using this method. They can also be cooked in a pressure cooker where they take about 40 minutes to prepare. Regardless of cooking method, do not add any seasonings that are salty or acidic until after the beans have been cooked since adding them earlier will make the beans more tough and will also increase the cooking time.