Soy has been associated with several health benefits, including promoting heart health, reducing menopause symptoms, and potentially lowering the risk of specific cancers. However, its long-term effects on growth, digestion, sexual maturation, thyroid health, and breast cancer risk also warrant consideration. Indeed, soy stands out as one of the most debated topics in nutrition.

On one side of the spectrum, soy is packed with essential nutrients, and diets incorporating soy are often linked to various health advantages, such as reduced blood sugar levels, enhanced cardiovascular health, alleviation of menopause symptoms, and possibly a decreased risk of certain cancers. Conversely, there are apprehensions regarding the health implications of a soy-rich diet. Some individuals worry that excessive soy consumption could elevate breast cancer risk, impair thyroid function, or lead to feminizing effects in men, among other concerns.

This article aims to explore the most recent scientific findings to assess whether the consumption of soy is more likely to yield beneficial or detrimental effects on health.

Rich in Nutrients

Soybeans are a powerhouse of nutrition, naturally abundant in protein and providing all essential amino acids necessary for optimal bodily function. In addition to their protein content, they are loaded with healthy plant fats, dietary fiber, and a range of vital vitamins, minerals, and beneficial phytochemicals. There is a wide array of products derived from soybeans, and below is a detailed comparison showcasing the nutrient profile of several popular choices per 100-gram serving:

Note: A hyphen in the table signifies that the nutrient data is not available in the FoodData Central database. Nevertheless, the food item may still contain that nutrient.

Beyond their impressive vitamin and mineral profile, soybeans are also a natural source of polyphenols, a category of antioxidants known for their potential to safeguard the body from cellular damage and various health issues, including cardiovascular diseases. Particularly noteworthy are the isoflavones found in soybeans, a specific type of polyphenol recognized as phytoestrogens due to their ability to bind to and activate estrogen receptors in the human body.

The health benefits associated with soy-based foods are often attributed to these soy isoflavones. Boiled soybeans can provide between 90 and 134 mg of isoflavones per 100 grams, depending on the soybean variety used. Due to their structural similarities, soy isoflavones are frequently thought to imitate the hormone estrogen. However, research indicates that soy isoflavones and estrogen differ significantly, each exhibiting distinct effects on human physiology.

In summary, soy and its derivatives are typically abundant in protein, fiber, vitamins, minerals, and antioxidants, alongside soy isoflavones, which are believed to confer an array of health advantages.

Potential Health Benefits of Soy-Rich Diets

Incorporating soy into your diet can lead to various health advantages that are worth exploring.

Cholesterol Level Management

Numerous studies have indicated that consuming soy-based foods might effectively lower LDL (bad) cholesterol while increasing HDL (good) cholesterol levels. A recent review highlighted that a daily intake of approximately 25 grams of soy protein could potentially decrease total and LDL cholesterol levels by about 3%. It is suggested that the reductions could be more significant when individuals swap out animal protein for soy protein, though further studies are needed to solidify this claim.

Another review noted that a diet rich in soy may lead to a reduction of total and LDL cholesterol levels by 2% to 3%, alongside a potential 3% increase in HDL cholesterol and a roughly 4% decrease in triglyceride levels. Notably, individuals with risk factors for heart disease, including high cholesterol, obesity, or type 2 diabetes, seem to experience the most benefits from consuming soy. Furthermore, whole, minimally processed soy foods like soybeans (soya), tofu, tempeh, and edamame appear to enhance cholesterol levels more effectively than their processed counterparts and supplements.

Heart Health Protection

Legume-rich diets, particularly those including soy, are associated with a reduced risk of heart disease. The isoflavones found in soy are believed to help diminish inflammation in blood vessels and enhance their elasticity, both of which are essential for maintaining heart health. A recent review connected soy-rich diets with a 20% lower risk of stroke and a 16% reduction in heart disease risk. Moreover, some studies propose that these diets might decrease the risk of mortality due to heart disease by up to 15%.

Blood Pressure Regulation

Foods derived from soybeans are abundant in arginine, an amino acid known for its role in blood pressure regulation. Additionally, soybeans are a good source of isoflavones, which may contribute to lowering blood pressure. One specific study showed that consuming 50 grams of soy nuts daily could reduce diastolic blood pressure in certain women by about 8%. Other research correlates daily intakes of 65 to 153 mg of soy isoflavones with reductions in blood pressure of 3–6 mm Hg among individuals with hypertension. However, it remains uncertain if these modest benefits extend to those with normal or slightly elevated blood pressure levels, necessitating further investigation into this area.

Blood Sugar Control

A systematic review, which included 17 randomized controlled trials—the gold standard in research—suggests that soy isoflavones may have a mild effect in lowering blood sugar and insulin levels specifically in menopausal women. These isoflavones might also assist in decreasing insulin resistance, a condition that can lead to elevated blood sugar levels and eventually contribute to type 2 diabetes. Furthermore, there is some evidence indicating that soy protein supplements could aid in slightly lowering blood sugar and insulin levels in individuals with type 2 diabetes or metabolic syndrome, characterized by a combination of conditions such as high blood sugar, elevated cholesterol levels, hypertension, and increased abdominal fat. However, results have not been consistent, and several studies have failed to establish a strong link between soy foods and blood sugar regulation in both healthy individuals and those with type 2 diabetes, highlighting the need for additional research.

Fertility Enhancement

Research suggests that women who consume soy-rich diets might experience improved fertility outcomes. One study indicated that women with higher intakes of soy isoflavones were 1.3 to 1.8 times more likely to conceive following fertility treatments compared to those with lower intakes. Interestingly, these benefits may not extend to men. Another study found that soy foods could provide some protection against bisphenol A (BPA), a chemical found in certain plastics that is believed to impair fertility. However, the evidence supporting fertility benefits from soy is not universally accepted. For example, one review suggested that consuming around 100 mg of soy isoflavones daily might negatively impact ovarian function and reproductive hormone levels. Furthermore, another review indicated that women consuming over 40 mg of soy isoflavones per day could face a 13% increased likelihood of fertility challenges compared to those with lower intakes. Nonetheless, most studies suggest that diets incorporating 10 to 25 mg—or even up to 50 mg—of soy isoflavones daily as part of a balanced diet do not adversely affect ovulation or fertility, equating to roughly 1 to 4 servings of soy foods each day.

Menopause Symptom Relief

Soy is rich in isoflavones, a group of compounds that function as phytoestrogens or plant estrogens due to their capacity to bind to estrogen receptors in the body. During menopause, as estrogen levels naturally decline, women may experience various unpleasant symptoms like fatigue, vaginal dryness, and hot flashes. By interacting with estrogen receptors, soy isoflavones are believed to help mitigate the intensity of these symptoms. Research indicates that soy isoflavones may reduce both the frequency and severity of hot flashes. They also seem to assist in alleviating fatigue, joint pain, depression, irritability, anxiety, and vaginal dryness during menopause and the transition years leading up to it. However, findings are not universally consistent, indicating that further research is necessary before establishing definitive conclusions.

Bone Health Improvement

Low estrogen levels during menopause can lead to calcium depletion from bones, resulting in a condition known as osteoporosis, characterized by weak and brittle bones. Emerging evidence suggests that daily intakes of 40 to 110 mg of soy isoflavones may help mitigate bone loss and enhance bone health markers in menopausal women. To contextualize this, this level equates to consuming approximately 140 to 440 grams of tofu or 35 to 100 grams of cooked soybeans each day.

Breast Cancer Risk Reduction

High soy diets have been associated with a diminished risk of certain cancers. A recent review encompassing 12 studies revealed that women with elevated soy consumption prior to a cancer diagnosis may experience a 16% lower risk of mortality from the disease compared to those with lower intake. Additionally, high soy consumption before and after a diagnosis may lower the risk of breast cancer recurrence in postmenopausal women by up to 28%, although premenopausal women may not see similar advantages. Conversely, another study indicated that both pre- and postmenopausal women following soy-rich diets might enjoy a 27% reduction in cancer risk, although the protective effects of soy were predominantly noted in Asian women, while Western women seemed to gain little benefit. Hence, while a segment of women adhering to soy-rich diets may experience a lower risk of breast cancer, further studies are essential to identify which women could benefit the most.

Reduced Risk of Other Cancers

In addition to breast cancer, soy-rich diets may contribute to lowering the risk of other cancer types. Research indicates that high intakes of soy isoflavones could correlate with a 19% reduction in endometrial cancer risk. Moreover, certain studies have linked soy-rich diets to a 7% decreased risk of digestive tract cancers and an 8% to 12% lower risk of colon and colorectal cancers, particularly among women. On the other hand, men consuming soy-rich diets may also see a reduced risk of prostate cancer. Lastly, a recent review encompassing 23 studies found that diets abundant in soy foods were associated with a 12% lower risk of cancer-related mortality, particularly for stomach, large intestine, and lung cancers. Overall, soy-rich diets appear to promote heart health, lower blood pressure, blood sugar, and cholesterol levels, and may enhance fertility, alleviate menopause symptoms, and offer protection against specific cancers. However, further research is warranted to deepen our understanding of these benefits.

Understanding the Concerns Surrounding Soy

Soybeans, along with various products derived from them, have been integral to human nutrition for countless generations. However, some individuals harbor apprehensions regarding the incorporation of soy into their dietary habits due to several notable concerns:

• Estrogen-like effects. The isoflavones found in soy are frequently believed to replicate the female reproductive hormone estrogen. While structurally similar to this hormone, soy isoflavones exhibit weaker and somewhat distinct effects compared to estrogen.
• Cancer risk. There is a perception among some that soy isoflavones might elevate the likelihood of developing breast or endometrial cancer. Nevertheless, the majority of research indicates no adverse impact; in fact, they may offer protective benefits against certain types of cancer.
• Thyroid health. While test-tube and animal research indicates that specific compounds in soy might impair thyroid gland function, human studies generally reveal little to no negative consequences, particularly in individuals with intact thyroid health.
• Feminizing effects in males. Concerns have been raised that soy isoflavones could hinder testosterone production in men. However, scientific studies show only a tenuous link between the two.
• Impact on infants. There is anxiety surrounding the notion that soy-based formulas could adversely affect the development of the brain, sexual characteristics, thyroid function, or immune system in infants. Yet, research typically fails to demonstrate any lasting negative effects from soy formula in healthy, full-term infants.
• Genetically Modified Organisms (GMOs). A significant portion of soybeans available in the market is genetically modified. Such GMO soy may possess fewer nutrients and higher herbicide residue levels compared to conventional or organic soy varieties. More extensive research is necessary to ascertain the long-term health implications of consuming GMO soy.
• Antinutrients. Soybeans harbor compounds that may hinder the body's capacity to absorb their vitamins and minerals effectively. Techniques such as soaking, sprouting, fermenting, and cooking can significantly diminish these antinutrient levels in soy products.
• Digestive complications. Animal studies indicate that the antinutrients present in soy could potentially compromise the gut's barrier function, leading to inflammation and digestive challenges. However, further human research is essential to validate these findings.

It's important to acknowledge that while these concerns are prevalent, only a handful are backed by robust scientific evidence. Furthermore, instances where negative effects were noted often occurred following the consumption of extraordinarily high quantities of soy.

For example, men who reported experiencing feminizing effects attributed to soy had ingested amounts nearly nine times greater than the average intake observed in those with soy-rich diets. For most individuals, achieving such high levels of soy consumption daily would be quite challenging. The above concerns are frequently mentioned in discussions about soy. In general, few hold up against rigorous scientific scrutiny, and additional research is necessary to validate the remaining apprehensions.

Understanding the Varieties of Soy-Based Foods

It is essential to recognize that not all soy foods possess the same nutritional profile or health advantages. Generally speaking, the less processed a soy product is, the higher it tends to be in vitamins, minerals, and other beneficial compounds. In contrast, highly processed soy items often contain a greater amount of salt, sugar, unhealthy fats, and unnecessary additives.

This is why minimally processed soy foods, such as soybeans (???????), tofu, tempeh, edamame, and unsweetened soy milks and yogurts, are regarded as more nutritious compared to heavily processed options like soy protein powders, imitation meats, energy bars, or sweetened soy products. Furthermore, minimally processed soy foods may provide additional benefits beyond their nutrient density; for example, they tend to be more effective in lowering blood sugar or cholesterol levels than their processed counterparts or supplements.

Moreover, fermented soy foods like soy sauce (???? ???), tempeh, miso, and natto are often viewed as more advantageous compared to non-fermented soy varieties. This enhanced benefit can be attributed to the fermentation process, which helps to diminish some of the antinutrients that are naturally present in soy products. This reduction enhances the body’s ability to absorb the valuable nutrients found in soy.

In addition to fermentation, cooking, sprouting, and soaking are effective preparation techniques that can further lower the antinutrient content of soy foods, thus improving their digestibility. To summarize, minimally processed soy foods like soybeans (???????), tofu, tempeh, edamame, and unsweetened soy milks and yogurts are superior to their highly processed counterparts, with fermented soy foods offering even greater health benefits.

The Bottom Line

Soybeans are an excellent source of essential nutrients and beneficial plant compounds. Incorporating minimally processed soy foods into your diet may lead to numerous health advantages, such as enhanced heart health, reduced symptoms during menopause, and a decreased risk of certain types of cancers. For instance, in India, dishes like soybean curry highlight the versatility of soy, while in Australia, soy milk has become a popular dairy alternative.

Nevertheless, there are concerns regarding the potential drawbacks of soy consumption. Issues such as the presence of genetically modified organisms (GMOs), the possibility of estrogen-like effects, and the long-term implications for growth, digestion, sexual maturation, thyroid function, and breast cancer risk have been raised. However, it's important to note that currently, only a few of these worries are substantiated by robust scientific evidence. Continued research is essential to fully understand these concerns. For those interested in integrating soy into their meals, selecting minimally processed options over heavily processed alternatives is advisable to maximize health benefits.