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Nutrition
Soy eating is safe through all life stages for babies, kids and adults, both among women and men. It has significant health benefits and advantages.
A new formal position paper of the Israel Ministry of Health. May 2017
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What’s New and Beneficial About Soybeans
World’s Healthiest Foods – health-promoting foods that can change your life. www.whfoods.com
We recognize that soybean consumption is a matter of much current debate. There has been much written about it on the Internet, with claims that eating soybeans can endanger your health.
To provide you with a comprehensive perspective on this topic, we have reviewed the research on soybeans. Throughout this food profile we have addressed the key controversial issues, focusing on them especially in our Health Benefits and Individual Concerns sections.
Researchers have recently asked a very simple question about soybeans: what would happen in terms of nutrition if U.S. citizens replaced their current intake of meat and dairy products with soy?
Using previously collected information on the U.S. population and average U.S. dietary intake, these researchers determined that replacement of meat and dairy with soy would result in significantly improved intake of folate and vitamin K; larger amounts of calcium, magnesium and iron; and 4 additional grams of fiber per day. At the same time, replacement of all meat and dairy with soy would lower average cholesterol intake by 123 milligrams per day and lower average saturated fat intake by 2.4 grams per day.
Protein would decrease somewhat (by approximately 8 grams per day, or 9% of average protein intake).
Given the relatively high average daily intake of protein in the U.S. (which in some cases, is nearly double the Dietary Reference Intake level), this 9% decrease in total protein intake does not seem problematic to us—making this “soy substitution” seem like good nutritional trade-off.
We’re not advocating replacement of all meat and dairy foods with soy! High-quality meat and dairy foods can play a very supportive role in many diets. But alongside of the many controversies swirling around soybeans and health, we think it’s important not to lose sight of the strong nutritional value of this legume.
Soybeans have long been recognized as a plant food that, when compared with other plants, is relatively high in protein.
Protein is the reason that soybeans have historically been called “meat of the field” or “meat without bones.” But only recently have researchers taken a very close look at the protein content of soybeans and arrived at some fascinating conclusions.
Even though soy protein is a plant protein and typically lower in certain amino acids (protein building blocks) than animal proteins like those found in chicken eggs or cow’s milk, once adjustments have been made for digestibility and other metabolic factors, soybeans turn out to receive a protein quality rating that is equal to the ratings for egg or cow’s milk.
When we think about antioxidant foods, the first foods that come to mind are usually vegetables. But recent research on soy has underscored many of the impressive antioxidant benefits that we get from this legume. No phytonutrient in soy has received more widespread attention than genistein—an isoflavone that has been extensively studied in relationship to cancer risk.
Yet, genistein is a soy component that could easily be singled out for its antioxidant properties! Increased activity of antioxidant enzymes—including superoxide dismutase, glutathione peroxidase, catalase, and glutathione reductase—has now been linked to intake of genistein from soy.
Another group of antioxidant phytonutrients called phenolic acids has also been recently investigated in soybeans. When we enjoy this antioxidant-rich legume, we also benefit from its phenolic acids, including caffeic, coumaric, ferulic, and sinapic acid.
WHFoods Recommendation
When including soybeans, try to stick with the whole food forms, and also consider giving preference to fermented versions like tempeh, fermented tofu, and soy miso.
Unfortunately, in the United States, we seldom consume soybeans in their whole natural form (either fresh or dried). Instead, we process soybeans by using hexane or other solvents to remove the oil (which can be sold as cooking oil or oil to be added to other processed foods), and then we take what’s left over (defatted soy flour) and either (1) combine it with other proteins to make animal feed or (2) wash it with water to create soy protein concentrate.
Soy protein concentrate becomes the source for two forms of soy that are even more processed: TVP, or textured soy protein that can be produced through a process called extrusion, and SPI (soy protein isolate), which can be produced by making the soy protein concentrate more solubilized. SPI is used in many low-fat soy milks.
All of the above processing steps create a soy product that is very different from the soybeans’ whole food form. A full-fat soy milk, for example, can be made by simply cooking whole soybeans in water and using a cloth to strain the soymilk (liquid) from the fibrous part of the cooked beans.
Tofu can be made from full-fat soy milk by using salts or acids to coagulate the milk into curds that can be pressed into “cakes.” (Tofu can be further preserved through fermentation.) Natto is another good example of a whole food form of soybean. Natto can be made by taking whole soybeans, adding a bacteria called Bacillus subtilis, and giving the bacteria time to ferment the beans. Natto, tofu, and full-fat soymilk are whole food forms of soybean that stand in sharp contrast to processed forms like TVP and SPI.
Since genetically modified (GM) soybeans have reached 90% market penetration in the United States select organically grown soy products to avoid GMO.
Public Health Recommendations Many public health organizations—including the American Diabetes Association, the American Heart Association, and the American Cancer Society—recommend legumes (the category in which soybeans are classified) as a key food group for preventing disease and optimizing health.
The 2005 Dietary Guidelines for Americans developed by the U.S. Department of Health and Human Services (USDHHS) and the U.S. Department of Agriculture (USDA) recommends 3 cups of legumes per week (based on a daily intake of approximately 2,000 calories). Because 1 serving of legumes was defined as 1/2 cup cooked, the Dietary Guidelines for Americans come very close to this as they recommend of 1/2 cup of cooked legumes on a daily basis. Based on our own research review, we believe that 3 cups of legumes per week is a very reasonable goal for support of good health. However, we also believe that optimal health benefits from legumes may require consumption of legumes in greater amounts. This recommendation for greater amounts is based upon studies in which legumes have been consumed at least 4 days per week and in amounts falling into a 1-2 cup range per day. These studies suggest a higher optimal health benefit level than the 2005 Dietary Guidelines: instead of 3 cups of weekly legumes, 4-8 cups would become the goal range.
Remember that any amount of legumes is going to make a helpful addition to your diet. And whatever weekly level of legumes you decide to target, we recommend inclusion of soybeans among your legume choices.
SoyBean Health Benefits - 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
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.
Metabolic differences
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.
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
daidzein
genistein
malonylgenistin
malonyldaidzin
Phenolic Acids
Caffeic acid
Coumaric acid
Ferulic acid
Gallic acid
Sinapic acid
Phytoalexins
glyceollin I
glyceollin II
glyceollin III
Phytoalexins
glyceollin I
glyceollin II
glyceollin III
Phytosterols
beta-sitosterol
beta-stigmasterol
campestrol
Proteins and Peptides
defensins
glycinin
conglycinin
lunacin
Saponins
soyasaponins (group A and group B)
soyasapogenols
Cardiovascular Benefits
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
TIncreased 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!)
What’s New and Beneficial About Soybeans
World’s Healthiest Foods – health-promoting foods that can change your life. www.whfoods.com