Soy has been associated with several potential health benefits, including promoting heart health, alleviating menopause symptoms, and possibly reducing the risk of certain cancers. However, it is crucial to consider that soy may also exert long-term effects on growth, digestion, sexual maturation, thyroid function, and breast cancer risk. This makes soy one of the most debated topics in nutrition.

On the positive side, soy is packed with essential nutrients, and research suggests that incorporating it into your diet may be linked to various health advantages, such as lower blood sugar levels, enhanced cardiovascular health, reduced menopause symptoms, and possibly even a decreased risk of some cancers. Conversely, there are valid concerns regarding the health implications of a diet high in soy. Some individuals worry that excessive soy consumption may elevate breast cancer risk, impair thyroid function, or lead to feminizing effects in men, among other issues.

This article aims to review the most recent scientific findings to assess whether the consumption of soy is more beneficial or harmful to your health.

Rich in Nutritional Value

Soybeans are a powerhouse of nutrition, naturally abundant in protein and providing all the essential amino acids that our bodies require. They boast a high content of plant fats, dietary fiber, and a variety of vital vitamins, minerals, and beneficial phytochemicals. There are numerous products made from soybeans. Below, you will find a comparison of the nutrient profiles of several widely consumed varieties, presented per 100 grams (3.5 ounces):

Apart from their rich vitamin and mineral composition, soybeans are also a natural source of polyphenols—antioxidants that may protect the body from cell damage and conditions such as heart disease. They are particularly abundant in isoflavones, a subtype of polyphenols known as phytoestrogens, which can bind to and activate estrogen receptors within the body.

The health benefits attributed to soy-based foods are thought to stem largely from soy isoflavones. Boiled soybeans have been found to contain between 90 and 134 mg of isoflavones per 100 grams, depending on the specific variety. Due to their structural similarities, soy isoflavones are often considered to mimic estrogen. However, research indicates that they differ from estrogen in various significant ways, each exerting unique impacts on the human body.

Potential Health Benefits of Soy-Rich Diets

Incorporating soy into your diet may offer a variety of health advantages worth considering.

May Aid in Lowering Cholesterol Levels

Numerous studies indicate that a diet abundant in soy foods can significantly decrease LDL (bad) cholesterol while boosting HDL (good) cholesterol levels. A recent meta-analysis revealed that consuming a median of 25 grams of soy protein daily could lower total and LDL (bad) cholesterol by roughly 3%. Furthermore, researchers believe that these reductions could be even more pronounced when individuals substitute soy protein for animal protein, although further studies are needed to validate this assertion.

Another review highlights that soy-rich diets might reduce total and LDL (bad) cholesterol levels by 2-3%, while also increasing HDL (good) cholesterol by approximately 3% and lowering triglyceride levels by nearly 4%. Individuals with existing risk factors for heart disease, such as elevated cholesterol, obesity, or type 2 diabetes, seem to gain the most from incorporating soy into their diets. Moreover, whole soy foods like soybeans, tofu, tempeh, and edamame tend to yield more favorable cholesterol results compared to processed soy products and supplements.

May Promote Heart Health

Incorporating legumes into your meals, particularly soy, may lower the risk of developing heart disease. Soy isoflavones have been shown to reduce inflammation in blood vessels and enhance their flexibility, both of which are vital for maintaining heart health. A recent review connects soy-rich diets to a 20% reduced risk of stroke and a 16% decline in heart disease risk. Additional research suggests that consuming soy foods might lower the likelihood of dying from heart disease by as much as 15%.

May Contribute to Lower Blood Pressure

Foods derived from soy, including soybeans, are generally rich in arginine, an amino acid known to help regulate blood pressure. Additionally, soy is packed with isoflavones, which are thought to provide blood-pressure-lowering effects. In a specific study, participants consuming about 43 grams (equivalent to 1/2 cup) of soy nuts daily experienced an approximate 8% reduction in diastolic blood pressure among some women. Other research indicates that daily intakes of 65-153 mg of soy isoflavones can lead to reductions of 3-6 mm Hg in individuals with hypertension.

Nonetheless, it remains uncertain whether these modest blood-pressure benefits extend to those with normal or mildly elevated blood pressure levels. While some studies suggest both groups may gain from soy's effects, others indicate that only individuals with high blood pressure may notice improvements. More research is essential to clarify this topic, as the current findings indicate that any blood-pressure-lowering effects of soy may be relatively minor.

May Help Regulate Blood Sugar

A comprehensive review encompassing 17 randomized controlled trials suggests that soy isoflavones might slightly decrease blood sugar and insulin levels in menopausal women. They may also improve insulin sensitivity, a condition that can lead to elevated blood sugar levels and potentially result in type 2 diabetes over time. Additionally, some evidence suggests that soy protein supplements could help lower blood sugar and insulin levels in individuals with type 2 diabetes or metabolic syndrome—a cluster of conditions that heighten the risk of type 2 diabetes, heart disease, and stroke.

However, findings on this topic are not unanimous, as several studies have failed to establish a strong connection between soy foods and blood sugar management in both healthy individuals and those with type 2 diabetes. Consequently, additional research is necessary before any definitive conclusions can be drawn.

May Enhance Fertility

Certain studies indicate that women consuming soy-rich diets may experience improved fertility outcomes. For instance, one study found that women with high soy isoflavone consumption were 1.3-1.8 times more likely to achieve pregnancy following fertility treatments compared to those with lower intakes. However, men may not experience similar fertility advantages. In another study, soy foods showed potential protective effects against bisphenol A (BPA)—a compound present in some plastics that is believed to negatively impact fertility.

Nonetheless, these supportive findings are not universally applicable. For example, a review noted that daily consumption of 100 mg of soy isoflavones could diminish ovarian function and reproductive hormone levels, both critical factors affecting fertility. Moreover, another review suggested that women consuming over 40 mg of soy isoflavones daily might face a 13% higher likelihood of fertility issues compared to those with intakes below 10 mg. However, most studies indicate that diets containing 10-25 mg—and potentially up to 50 mg of soy isoflavones per day—within a balanced diet do not seem to adversely affect ovulation or fertility, corresponding to approximately 1-4 servings of soy foods per day.

May Alleviate Menopausal Symptoms

Soy is rich in isoflavones, compounds known as phytoestrogens, which can bind to estrogen receptors in the body. During menopause, women's estrogen levels naturally decline, leading to symptoms like fatigue, vaginal dryness, and hot flashes. Soy isoflavones are believed to help mitigate the severity of these symptoms by interacting with estrogen receptors. Research suggests that soy isoflavones may decrease the intensity and frequency of hot flashes while also alleviating fatigue, joint pain, depression, irritability, anxiety, and vaginal dryness experienced during menopause and the preceding years.

May Support Bone Health

Low estrogen levels during menopause can lead to calcium depletion from bones, resulting in bone loss and increasing the risk of osteoporosis—a condition characterized by fragile bones. Some evidence indicates that daily intakes of 40-110 mg of soy isoflavones may help reduce bone loss and enhance bone health markers in menopausal women. To put this into perspective, this would equate to consuming approximately 140-440 grams (5-15.5 ounces) of tofu or 35-100 grams (1/3-1 cup) of cooked soybeans each day.

May Lower the Risk of Breast Cancer

Research has also associated soy-rich diets with a reduced risk of specific cancers. For instance, a recent review of 12 studies found that women with high soy intakes before their cancer diagnosis had a 16% lower risk of mortality from the disease compared to those with the lowest intakes. Additionally, high soy consumption before and after diagnosis may reduce the likelihood of breast cancer recurrence in postmenopausal women by up to 28%. However, this benefit does not appear to extend to premenopausal women.

Conversely, another study suggested that both pre- and postmenopausal women consuming soy-rich diets might experience a 27% reduced cancer risk. Notably, the protective benefits of soy were primarily observed in Asian women, with Western women showing minimal advantages. Collectively, these findings imply that some women following soy-rich diets may enjoy a lower risk of breast cancer, though more studies are warranted to identify which groups may benefit the most.

May Reduce the Risk of Other Cancer Types

Soy-rich diets may also contribute to a decreased risk of various other cancers. Research suggests that high soy isoflavone consumption may lower the risk of endometrial cancer by about 19%. Additionally, some studies have linked soy-rich diets to a 7% reduced risk of cancers in the digestive tract and an 8-12% lower risk of colon and colorectal cancers, particularly among women. In contrast, men consuming soy-rich diets appear to have a lower risk of prostate cancer.

Lastly, a recent review encompassing 23 studies tied soy-rich diets to a 12% lower risk of cancer mortality, especially for cancers affecting the stomach, large intestine, and lungs. Overall, soy-rich diets may enhance heart health while lowering blood pressure, blood sugar, and cholesterol levels. They might also promote fertility, alleviate menopausal symptoms, and provide protection against certain cancers. However, further research is necessary to fully understand these effects.

Understanding the Concerns Surrounding Soy

Soybeans and their derivatives have been integral to human nutrition for centuries. However, various apprehensions exist regarding soy consumption, which can be summarized in several key areas:

• Estrogen-like Properties. Soy isoflavones are frequently believed to imitate the female hormone estrogen. While their structure resembles that of estrogen, these isoflavones exhibit weaker and slightly different effects compared to the hormone.
• Cancer Concerns. Some individuals fear that soy isoflavones might increase the likelihood of breast or endometrial cancer. Yet, most research tends to show no adverse effects, and in some instances, may even provide protective benefits against certain cancers.
• Impact on Thyroid Health. Laboratory and animal studies propose that certain compounds in soy may impair thyroid function. Nevertheless, human studies typically indicate minimal to no negative effects, particularly among those with normal thyroid function.
• Effects on Male Hormones. There are worries that soy isoflavones could diminish testosterone production in men. However, human investigations reveal a weak association between soy intake and testosterone levels.
• Concerns for Infants. Some express anxiety that soy-based formula may adversely influence brain, sexual, thyroid, or immune development in infants. However, studies generally find no long-term negative impacts from soy formula in healthy, full-term infants.
• Genetic Modification Issues. Many soybeans are genetically modified (GMO). Such soy might have lower nutrient content and increased herbicide residues compared to conventional or organic varieties. Further research is essential to evaluate the long-term health implications of consuming GMO soy.
• Presence of Antinutrients. Soybeans contain substances that could hinder the body’s ability to absorb essential vitamins and minerals. Techniques such as soaking, sprouting, fermenting, and cooking can help mitigate these antinutrient levels.
• Potential Digestive Issues. Animal studies suggest that the antinutrients in soy may compromise gut barrier function, potentially leading to inflammation and digestive problems. However, additional human studies are required for confirmation.

It is important to recognize that while these concerns are commonly voiced, few are substantiated by robust scientific evidence. Moreover, when adverse effects are reported, they usually stem from the consumption of excessively large quantities of soy. For example, men who experienced feminizing effects from soy intake consumed amounts that were up to nine times greater than the average for individuals with soy-rich diets. Therefore, it would be quite challenging for most people to consume such high levels of soy daily.

Understanding the Varieties of Soy-Based Foods

It is essential to recognize that not all soy products offer the same nutritional advantages or health benefits. Generally speaking, the less processed a soy product is, the richer it tends to be in essential vitamins, minerals, and beneficial compounds. Conversely, soy foods that undergo extensive processing are likely to contain higher levels of salt, sugar, unhealthy fats, and unnecessary additives.

This distinction emphasizes the superiority of minimally processed soy foods—such as soybeans (soya), tofu, tempeh, edamame, and unsweetened soy milks and yogurts—over highly processed options like soy protein powders, imitation meats, energy bars, or sweetened soy products. Minimally processed varieties not only retain more nutrients but may also provide health benefits beyond their nutrient profile. For example, studies suggest that these foods are more effective in lowering blood sugar or cholesterol levels compared to their processed counterparts or supplements.

Moreover, fermented soy products, including soy sauce, tempeh, miso, and natto, are often regarded as having superior health benefits compared to non-fermented soy items. The fermentation process helps mitigate some of the antinutrients naturally present in soy, thus enhancing nutrient absorption in the body. Techniques such as cooking, sprouting, and soaking can also diminish antinutrient levels in soy products, improving their digestibility.

The Bottom Line

Soybeans are an abundant source of nutrients and valuable plant compounds. Diets incorporating minimally processed soy products can provide a range of health benefits, such as enhanced heart health, reduced symptoms during menopause, and a decreased risk of specific types of cancers. In various cultures, such as those in India and Japan, soy foods like tofu (??) and edamame are staples that contribute to balanced diets.

Despite these advantages, some individuals express concerns regarding potential downsides associated with soy consumption, including issues related to its genetically modified organism (GMO) content, possible estrogen-like effects, and its long-term impact on growth, digestive health, sexual development, thyroid function, and breast cancer risk. It is worth noting, however, that many of these worries lack substantial scientific backing. Nonetheless, further research is essential to fully understand these implications. For those looking to incorporate soy into their meals, opting for minimally processed alternatives, as seen in Australian and Canadian diets, is advisable over heavily processed varieties.