Soy is arguably one of the more controversial nutrition topics. On the plus side, soy is rich in nutrients, and diets containing it seem to provide health benefits, such as lower blood sugar levels, improved heart health, fewer menopause symptoms, and perhaps even a lower risk of certain cancers.
On the other hand, some people are concerned about soy-rich diets being truly healthy, and in fact, perhaps even being bad for your health. For instance, some fear that eating too much soy may increase the risk of breast cancer, hinder thyroid function, or have feminizing effects in men, to name a few. Furthermore, any soy you get in the US is most certainly a GMO (94 percent of the soybean crops in the United States were genetically modified to be herbicide-tolerant), which has implications for your health (think Glyphosate and Leaky Gut Syndrome leading to chronic inflammation).
This article reviews the latest scientific evidence to determine whether eating soy is more likely to positively or negatively affect your health.
Where Is Soy in our Diet?
As a food additive in our diet, soy appears most often broken down into isolated components: soybean oil, soy protein isolates, soy isoflavones, and soy lecithin are just some examples, but these examples are quite commonly found in much of our processed foods. You may think you don’t eat a diet heavy in soy, especially if you are not a vegetarian. But once you start looking under the surface, soy is hiding in many processed foods and in places you would find highly unlikely. You will find soy in meats (yes, meats — as a filler), salad dressings, low-carb versions of high-carb foods, cereals, and many other processed foods.
Beyond mysteriously occurring in one way or another in so many of our processed foods, many soy-based products are part of our regular diets such as tofu, soy sauce, soy milk, and soybean oil. There are so many more that we may or may not be familiar with:
Soy Products
The historical reason for this east Asian native legume being so commonly used in so many Asian preparations is that it is easy to grow, harvest, and store, it is nutritious and incredibly versatile.
The reason is it so common most recently in our Western diet is that soy is an extremely cheap and abundant source of protein. Second, only to corn, soy is one of the largest crops produced by the United States.
In the 1950s, the food industry had a waste problem (or opportunity) on their hands. While soy oil was used extensively in processed foods, it left the remaining components of the soybean, namely the protein, as a waste byproduct. Being efficient and profit-minded, food processors began to aggressively market soy protein as a healthy, vegetarian substitute for meat and dairy to those that were health-conscious or concerned about animal cruelty.
Soybeans (a legume) are related to clover, peas, and alfalfa. They are incredibly versatile as a food, but they are also used in thousands of products such as soaps, cosmetics, plastics, clothing, inks, glues, lubricants, coatings, and insulation.
The consistency of soybeans allows them to be transformed into oils and flours, as well as dairy and meat substitutes. Importantly, isolated soy proteins are used to emulsify fat and bind water, which keeps many products’ moistness without affecting other ingredients.
Soy lecithin is often used in chocolate, margarine, and cheeses to keep their ingredients from separating and clumping. The isolates can also be used to give an elastic gel texture, which can make drinks such as soy lattes seem more creamy or full-bodied.
Besides possessing remarkable flexibility, soybeans are also one of the most inexpensive crops to grow. Additionally, they can thrive in a wide variety of climates. These factors explain why they are so desirable for a range of industries. Although the plant originated in Asia, the vast majority of the world’s supply is currently grown in the United States and South America.
Not all soy-based foods are the same
It’s worth mentioning that not all soy foods are equally nutritious or beneficial.
Generally, the less processed soy food is, the more vitamins, minerals, and beneficial compounds it may contain. On the other hand, the more processed soy food is, the more salt, sugar, fat, and unnecessary additives and fillers it likely contains.
That is why minimally processed soy foods, such as soybeans, tofu, tempeh, edamame, and unsweetened soy milks and yogurts, are considered, from a health perspective, to be superior to soy-based protein powders, mock meats, energy bars, or sweetened soy-based milk products.
Furthermore, minimally processed soy foods may also offer benefits beyond those associated with their nutrient content. For example, they appear more effective at reducing blood sugar or cholesterol levels than processed soy-based foods or supplements (13, 20).
Additionally, fermented soy foods, such as soy sauce, tempeh, miso, and natto, are often considered more beneficial than non-fermented soy products. That is because fermentation helps reduce some of the anti-nutrients naturally found in soy foods (60).
Reducing some of the anti-nutirents found in soy can help improve your body’s ability to absorb those nutrients found in soy. Cooking, sprouting, and soaking are additional preparation techniques that can help reduce the anti-nutrient content of soy foods and enhance their digestibility (60, 61, 62, 63).
The Benefits of Soy
There list of benefits related to soy-based foods has much more substantiated body of scientific research to back it up. However, recall that there is a huge commercial impetus for funding this research, as there is a lot of money in this crop.
Contains various nutrients
- Soybeans are naturally rich in protein and contain all of the essential amino acids your body needs. They are also rich in plant fats, fiber, and several important vitamins, minerals, and beneficial plant compounds.
- In addition to their vitamin and mineral content, soybeans are a natural source of polyphenols, such as isoflavones, a type of antioxidant that may help protect your body against cell damage and conditions like heart disease (7, 8, 9, 10).
Contains polyphenols like isoflavones. Soybeans are especially rich in isoflavones, a subclass of polyphenols referred to as phytoestrogens due to their ability to attach to and activate estrogen receptors in your body (7).
- Soy isoflavones are believed to be one of the main reasons behind the many purported health benefits of soy-based foods. Boiled soybeans contain 90–134 mg of isoflavones per 3.5 ounces (100 grams), depending on the variety (7, 11).
- Due to their similarity in structure, soy isoflavones are often believed to mimic the hormone estrogen. However, research suggests that soy isoflavones differ from estrogen in many ways, with each having unique effects on the human body (12).
- Still, this is a good example of the pro and con nature of soy. There are as many, if not more, concerns about this estrogenic effect resulting from too much soy in our diet.
May help lower cholesterol levels. Several studies suggest that diets rich in soy foods may help lower LDL (bad) cholesterol and raise HDL (good) cholesterol (13, 14, 15).
- For instance, one recent review suggests that a median intake of 25 grams of soy protein per day may help reduce total and LDL (bad) cholesterol levels by around 3% (14).
- It could also be, in practice, that reductions may be larger when people eat soy protein instead of animal protein. However, more research is needed to confirm this (14). In addition, minimally processed soy foods, such as soybeans, tofu, tempeh, and edamame, appear to improve cholesterol levels more than processed soy products and supplements (13).
May help protect heart health.
- Diets rich in legumes, including soy, may help lower your risk of heart disease (16).
- It appears that soy isoflavones may help reduce inflammation in blood vessels and improve their elasticity — two factors believed to protect the health of your heart (17).
- A recent review further links soy-rich diets to a 20% and 16% lower risk of stroke and heart disease, respectively (18).
- Additional research suggests that diets rich in soy foods may reduce your risk of dying from heart disease by up to 15% (19).
May lower blood pressure.
- Soybeans and foods made from them are generally rich in arginine, an amino acid believed to help regulate blood pressure levels (20).
- Soybeans are also rich in isoflavones, another compound that is believed to offer blood-pressure-lowering benefits.
- In one study, eating 1/2 cup (43 grams) of soy nuts on a daily basis was found to reduce diastolic blood pressure (the bottom number of a blood pressure reading) by around 8% in some, but not all women (21).
- Other studies link daily intakes of 65–153 mg of soy isoflavones to blood pressure reductions of 3–6 mm Hg in people with high blood pressure (22).
May lower blood sugar.
- One review, including 17 randomized control studies — the gold standard in research — suggests that soy isoflavones may help slightly reduce blood sugar and insulin levels in menopausal women (24).
- Soy isoflavones may also help lower insulin resistance, a condition in which cells no longer respond to insulin normally. Over time, insulin resistance can result in high blood sugar levels and lead to type 2 diabetes (24).
- In addition, there’s some evidence that soy protein supplements may help slightly lower blood sugar and insulin levels in people with type 2 diabetes or metabolic syndrome (15).
May improve fertility. Some research suggests that women eating soy-rich diets may benefit from improved fertility.
- In one study, women with high intakes of soy isoflavones were 1.3–1.8 times more likely to give birth following fertility treatments than those with lower soy isoflavone intakes. However, men may not experience the same fertility-boosting benefits (28, 29).
- In another study, soy foods were found to offer some protection against the effects of bisphenol A (BPA), a compound found in some plastics believed to reduce fertility (30).
May reduce menopause symptoms.
- Soy is rich in isoflavones, which is a class of compounds, also referred to as phytoestrogens, or plant estrogens, due to their ability to bind to estrogen receptors in the body.
- During menopause, a woman’s estrogen levels naturally decrease, resulting in unpleasant symptoms, such as fatigue, vaginal dryness, and hot flashes. By binding to estrogen receptors in the body, soy isoflavones are believed to help somewhat reduce the severity of these symptoms.
May improve bone health.
- The low estrogen levels experienced during menopause may cause calcium to leach from the bones. The resulting bone loss may cause postmenopausal women to develop weak and brittle bones, a condition known as osteoporosis.
- Some evidence suggests that intakes of 40–110 mg of soy isoflavones per day may reduce bone loss and improve markers of bone health in menopausal women. However, more research is needed to confirm these findings (37, 38).
May reduce the risk of breast cancer. Diets rich in soy have also been linked to a lower risk of certain cancers.
- For instance, one recent review of twelve studies suggests that women with high soy intakes prior to receiving a cancer diagnosis may be at a 16% lower risk of dying from the condition, compared with those with the lowest intakes (39).
- High soy intakes pre- and post-diagnosis may also reduce the risk of breast cancer recurrence in postmenopausal women by up to 28%. However, and interestingly, this study alos suggests that premenopausal women may not experience the same benefit (39).
May reduce the risk of other types of cancer. Soy-rich diets may also help lower the risk of other types of cancer.
- For instance, studies suggest that high intakes of soy isoflavones may reduce the risk of endometrial cancer by around 19% (41, 42).
- In addition, some studies have linked soy-rich diets to a 7% lower risk of digestive tract cancers and an 8–12% lower risk of colon and colorectal cancers, especially in women (43, 44, 45). On the other hand, men eating soy-rich diets may benefit from a lower risk of prostate cancer (46).
The Concerns Related To Soy
Soybeans and foods derived from them have been part of the human diet for centuries. Nevertheless, some people worry about including soy in their diet due to the following areas of concern:
- Soy impacts our body’s ability to absorb critical vitamins and minerals.
- Soy contains trypsin inhibitors that inhibit protein digestion and affect pancreatic function;
- Soy contains phytic acid, which reduces the absorption of minerals like calcium, magnesium, copper, iron, and zinc;
- Soy increases our requirement for vitamin D, which 50% of American are already deficient in
- Vitamin B12 analogs in soy are not absorbed and actually increase the body’s requirement for B12
- Processed soy can contain toxins and carcinogens. Processing of soy protein results in the formation of toxic lysinoalanine and highly carcinogenic nitrosamines.
- Some soy contains MSG. Free glutamic acid or MSG, a potent neurotoxin, is formed during soy food processing, and additional amounts are added to many soy foods to mask soy’s unpleasant taste; and,
- Estrogen-mimicking effects. Soy isoflavones are often thought to mimic the female reproductive hormone estrogen. Although they’re similar in structure to this hormone, soy isoflavones have weaker and slightly different effects than estrogen (12).
- Soy can stimulate the growth of estrogen-dependent tumors and cause thyroid problems, especially in women.
- “In 1992, the Swiss Health Service estimated that women consuming the equivalent of two cups of soy milk per day provides the estrogenic equivalent of one birth control pill. That means women eating cereal with soy milk and drinking a soy latte each day are effectively getting the same estrogen effect as if they were taking a birth control pill.”
- Soy phytoestrogens disrupt endocrine function and have the potential to cause infertility and to promote breast cancer in adult women.
- Some people believe that soy isoflavones may raise the risk of breast or endometrial cancer. Yet, most studies find no negative effect. In some cases, they may even offer some protection against certain cancers (12, 39, 40, 47, 48).
- Thyroid function. Test-tube and animal studies suggest that some compounds found in soy may reduce thyroid gland function. Yet, human studies find little to no negative effects, especially in humans with healthy thyroid function (49, 50, 51).
- Feminizing effects in men. Some worry that soy isoflavones may reduce the production of the male hormone testosterone. However, human studies find a weak link between the two (12, 52). “Perhaps most alarmingly, a study at the Harvard Public School of Health in 2008 found that men who consumed the equivalent of one cup of soy milk per day had a 50% lower sperm count than men who didn’t eat soy.”
- Danger to babies. Some fear that soy formula may negatively affect brain, sexual, thyroid, or immune development. Yet, studies typically fail to observe any long-term negative effects of soy formula in healthy, full-term babies (53, 54, 55, 56). “Babies fed soy-based formula have 13,000 to 22,000 times more estrogen compounds in their blood than babies fed milk-based formula. Infants exclusively fed soy formula receive the estrogenic equivalent (based on body weight) of at least five birth control pills per day.”
- GMOs. Soybeans are often genetically modified (GMO). GMO soy may contain fewer nutrients and more herbicide residues than conventional or organic soy. More research about the long-term health effects of GMO soy is needed (57, 58). But is is important to note that crops like soy are often heavily doused with the herbacide Round-up shortly after planting, in preparation for harvest, and most concerning as a descicant prior to storage. Glyphosate, the active ingredient in in Roundup, is believed to be a factor in Leaky Gut Syndrome.
- Anti-nutrients. Soybeans contain compounds that may lower the body’s ability to absorb the vitamins and minerals they contain. Soaking, sprouting, fermenting, and cooking are ways to reduce these anti-nutrient levels in soy (59, 60, 61, 62).
- Digestive issues. Animal studies suggest that the anti-nutrients in soy may reduce the gut’s barrier function, possibly resulting in inflammation and digestive issues. However, more human studies are needed to confirm this (63, 64, 65).
Keep in mind that while these concerns are common, generally speaking, the are not supported by scientific research at this time. Moreover, when negative effects have been observed, they often followed the consumption of very large amounts of soy (more on that in when we get to the Bottom Line).
For example, those men who reported experiencing feminizing effects from soy consumed amounts as high as 9 times larger than the average intake of men with soy-rich diets. so, while it is possible, in reality, would be difficult for most people to eat that much soy each day (12).
The Bottom Line
Soybeans are rich in nutrients and beneficial plant compounds. They offer a economical and highly versatile alternative for those choosing a plant-based diet. Diets rich in minimally processed or fermented soy foods may offer various health benefits, including improved heart health, fewer menopause symptoms, and a lower risk of certain cancers.
However, those that do research and try to be informed about thieir diet may worry about soy’s potential downsides, including possible toxins and carcinogens, its GMO content, possible estrogen-like effects, and long-term influence on growth, digestion, sexual maturation, thyroid health, and breast cancer risk.
Currently, much of the concerns raised regarding the potentially negative effects of soy in our diet still need further scientific research to substaintiate those concerns.
Like any alternative, such as sugar substitues, fat substitutes or even the birth control pill, any solution to one problem brings its own unique collection of pros and cons. At this time, the safe bet would seem to be to have well-rounded diet that does not include too much of any one thing including soy-based ingredients.