HEALTH MYTHS ABOUT SOY: IS SOY GOOD FOR YOU? (PART 2)
Medically Reviewed by Dr. Rosmy Barrios - September 16, 2024
The following article forms part 2 of a discussion on the health effects of soy and whether soy is good for you or not. Health benefits, safety, contraindications and considerations with regard to soy products are detailed below.
Are There Health Benefits to Consuming Soy?
When prepared in a way that conserves soy’s nutritional profile, soy has been proven to offer numerous health benefits. Long-term consumption in moderation appears to promote the following effects on health[1]:
- Bone. Through their estrogenic effects, Isoflavones may help in preventing osteoporosis particularly in postmenopausal women.[2]
- Cognition. Soy products appear to improve cognition in women, and have a varying impact on cognition in men[3]. The Isoflavones in soy may reduce the risk of Alzheimer’s disease in women. Very high consumption of non-fermented soy products is associated with reduced cognition in Asian populations over the age of 65.[4] These products have a low isoflavone content, suggesting that Isoflavones are the main neuro-protective factor in soy foods. Indeed Isoflavones have been shown to protect against age-related neuronal loss.
- Lipid metabolism. Soy appears to increase HDL cholesterol and reduce LDL cholesterol in those with very high levels. In those with healthy cholesterol levels, soy did not unbalance cholesterol levels. Furthermore, it has been shown that isoflavones prevent the oxidation of LDL cholesterol by incorporating themselves inside LDL molecules, thus protecting against vascular inflammation and heart disease.[5]
- Vascular. Soy Isoflavones have been shown to increase vasodilation, thereby promoting optimal circulation[6]. The lipid regulating functions of soy components also serve to reduce vascular inflammation, thereby improving vascular function.
- Immune Function. The proteins present in soy have been shown to enhance natural killer cell function, regulate inflammation and promote phagocytosis.[7] Isoflavones have been noted to increase many immune-boosting antioxidant compounds in the body such as glutathione and superoxide dismutase.
Soy has been shown to be protection against a number of health conditions, including:
Type 2 Diabetes. Compared to other legumes, soy has a very low glycemic load, likely due to the high fat and protein content. [8] Coupled with the isoflavone and protein content, soy products have been shown to lower the risk of type 2 diabetes. These affects pertain to lowering inflammation, regulating insulin secretion and protecting pancreatic beta cells. Soy oil may increase the risk (see below).
- Cancer. Aside from breast and prostate cancer, soy consumption is inversely associated with lung cancer[9].
- Chronic infection. Soy Isoflavones possess antimicrobial effects against certain antibiotic-resistant infections, including staphylococcus aureus and enterococcus strains[10].
- Cardiovascular disease. Soy isoflavone, in combination with taurine from fish, were shown to contribute towards the low rates of coronary heart disease observed in the Japanese population.[11] This is attributed towards increased HDL cholesterol and folate levels.
- Muscle Wasting. Soy protein glycinin may protect against muscle atrophy induced by nerve damage, as evidenced in animal studies.[12]
- Anxiety. While the effects are likely to be minimal, soy protein contains a fraction of opioid peptides with anxiolytic actions[13]. If not absorbed into systemic circulation, these peptides serve to relax the digestive tract, suppress appetite, and slow transit time.
Safety Profile of Soy
Soy is generally regarded as safe to consume; particularly as no adverse effects have been reported in Asian populations where soy has been a staple food for thousands of years. For much of its history, soy was prepared using traditional methods, such as fermentation, which enhances its nutritional profile.
Processing soy with heat is known to have an impact on the nutritional value of the final product. No adverse effects have been associated with soy products made using traditional heat-processing methods, such as traditional tofu and tempeh.
Other refined soy products may pose a risk to health over time due to confounding variables, such as Bisphenol-A packaging (estrogenic plastic pollutant), additives, low nutrient density, and poor digestibility. Examples include mass-produced tofu, protein isolates, and soy milk. Additionally, soybean oil may promote inflammation due to being overly oxidized during the extraction process.
Does Soy Have Contraindications?
Most of the data supports that soy is safe to consume for the majority of the population. Individuals with the following conditions may want to restrict soy intake:
Diabetes
Soy may be contraindicated for young men with type 1 diabetes[14]. A study highlighted how a 19-year old man suffered decreased free testosterone, hypogonadism, and erectile dysfunction while consuming a vegan diet high in soy products. These conditions often occur secondary to diabetes, which suggests that consuming a high-soy diet may exacerbate symptoms of diabetes.
These effects may depend on the type of soy product consumed. Soy protein, Isoflavones and tofu were associated with a reduced risk of type 2 diabetes, however whole soy is not[15].
Those with fatty liver disease, obesity, and conditions prone to chronic pain may want to moderate their consumption of unmodified soy oil due to the high concentration of omega-6 fatty acids. Modified soy oil comprises of far less omega-6 fats. The majority of other soy products contains little to no oil and are therefore not as much of a concern in this regard.
DHEAS Deficiency
A daily dose of 15g soy protein with extra Isoflavones served to reduce androstenedione and DHEAS (minor forms of testosterone) in postmenopausal women over the course of 6 months. These results were not reflected in male participants, nor the control group that consumed soy protein without isoflavones. Levels of adrenal hormones, normal testosterone, and estradiol were unaffected in all participants.[16]
Glutamate Sensitivity
Soy sauce, soy protein isolate, and many other soy products are known to contain high levels of free glutamate. Glycinin in the soybean comprises of between 21-35% free glutamate. Free glutamates are present in multiple different forms, each with different effects on human health.
Monosodium glutamate (MSG) is one form of glutamate that is associated with adverse long-term health outcomes. While it is known to enhance the flavor of foods, it promotes obesity[17], neuronal excitotoxicity, and immune dysfunction (especially known to affect white blood cells in the spleen). Those who are sensitive to MSG may want to avoid soy-based products or consume them in strict moderation to avoid ingesting MSG. This includes obese individuals, hyperallergenic individuals, and those with mood disorders[18], heart conditions, liver disease, or neurological conditions.[19]
Casein Allergy
Those with digestive issues, reduced digestive enzymes, allergies and food sensitivities may want to cut soy out of their diet along with grains, nuts and seeds until digestive function has been restored. Those who are allergic to casein may be similarly allergic to soy.
Whey Protein and Dairy Products
Studies carried out on the processing of soy proteins in combination with dairy products suggests that soy is capable of increasing the amount of free kappa-casein and beta-lactoglobulin in dairy products[20]. Both of these have been detected in the breast milk of women who consume dairy products[21]. Kappa-casein is implicated as a tumor marker in early stage breast cancer[22], however the usual levels found in cows milk are negligible (10% vs 55% in human milk). Soy proteins may marginally increase the risk in this regard.
Beta-lactoglobulin is a known food allergen that occasionally is expressed in the milk of mothers consuming dairy. It is a prime constituent of whey protein. Some infants and individuals are allergic to beta-lactoglobulin. Thus, these individuals and breast-feeding mothers may want to avoid consuming dairy products and whey protein, particularly those enriched with soy proteins. Commercial mass-produced chocolate, energy bars and protein shake powders are common examples of food enriched with both types of protein.
Endocrine Disorders
There have been a few scarce case reports of women suffering dysmenorrhea and symptoms of endometriosis due to soy consumption[23]. Symptoms did not fully abate when soy was removed from the diet, however they improved, suggesting a pre-existing endocrine condition for which soy is contraindicated. Thyroid disorders are closely associated with dysmenorrhea and reproductive diseases[24]. Thus, it is recommended to limit the intake of soy if suffering from a thyroid condition.
Benefiting Optimally from Soy Products
While soy is generally associated with many health promoting effects, various preparations of soy may be more suitable for health depending on the circumstance. The following highlights a few known differences between types of soy products.
Soy Processing
As highlighted above, the antinutrients in soy products are predominantly what brought it disrepute, while the nutrients promote optimal health and well-being for most individuals.
Consuming minimally refined soy products appear far more beneficial than soy extractions, particularly for cholesterol and fat metabolism.[25] These products typically have a higher nutrient content, which means they tend to convey more benefit to health overall. Some processing techniques have begun to remove most of the antinutrients from soy products, enhancing the isoflavone content and minimizing potential harm from chronic consumption.
Fermentation is optimal
Soy products that have been processed using a high moisture content and low temperature tend to retain a lot of the nutritious components of soy. Fermented soy products that have been prepared in the absence of heating or prior processing are thus optimal.
Soy sauce, tempeh, traditional tofu and miso are examples of soy ferments that are usually processed in this manner. However, some producers may still boil the contents beforehand in order to speed up production. Traditionally fermented soy products have the highest nutritional content and are fermented for longer times, serving to enzymatically degrade the antinutritional components before consumption.
Agricultural Variance
The nutrient content of soy is not constant across all strains and countries where the crop is cultivated. Studies indicate that soy produced in Korea and the US have the highest isoflavone content, with Japan, China and Australia being close contenders. Varieties from Europe, Brazil and Taiwan were considerably lower in isoflavone content.[26]
Other Soy Product Considerations
Due to the wide variety of soy-based products on the market, each product tends to have its own unique pros and cons. Here are some additional considerations to think of when evaluating soy products on the shelf:
- The majority of mass-produced soy products have a very low isoflavone content, often as a result of heat processing. Refined chocolate is a prime example.[27]
- Soybean oil ought to be consumed in moderation with other healthy plant-based oils to make the most of its health benefits and minimize potential consequences.
- Soy protein isolates are the highest in glutamate and are also the most difficult fraction of soy to digest. Nonetheless, they protect against muscle wasting, relax the gut, and can confer several cholesterol-regulating benefits.
- Protein from soy should not be mixed with milk protein, particularly during processing that involves heat as this may increase the release of carcinogenic compounds in the dairy fraction.
- Non-fermented soy products are high in soy protein and low in anti-inflammatory nutrients, however, they are likely more digestible than soy protein isolates due to the carbohydrate content.
- Soy kibe and soy sausage are known to have a higher isoflavone content on average compared to other purely soy-based foods. However, the amount of isoflavone in these products varies considerably and is still present in small quantities.
- Fermented products are the most bioavailable sources of soy nutrients.
- Fermented soy products such as natto and miso are fermented with beneficial molds and yeasts, which may be contraindicated in those with penicillin allergy or sensitivity to these organisms.
- Wheat is often added to fermented soy products like soy sauce, which increases the glutamate content and detracts from the nutritional content of soy.
- Liquid products are easier to absorb nutrients from than solid products, however, as many liquid products are often boiled during processing, they contain far less nutrients.
- Soy sauce is high in sodium, glutamate and monosodium glutamate (MSG). In some instances, MSG is added as an extra ingredient to enhance flavor.
- Soy milk and several processed soy products are packaged in plastic that may contain BPA. BPA has been shown to be an endocrine disruptor and may substantially enhance the hormonal actions of soy products.
Soy as Part of a Balanced Diet Plan
Just remember that one’s diet ought to be varied and not rely too heavily on any one given food!
In spite of their general safety and health benefits, soy products ought to be consumed in moderation, within the context of a balanced, healthy, and nutritious diet.
While many components of soy are easy to digest, soy contains two well-known protease inhibitors (lunasin and Bowman-Birk) which detract from protein digestion. As soy contains much higher protein than prebiotic fiber, it is likely best consumed as part of a plant-based diet rich in fiber and wholefoods containing digestive enzymes.
Whole grains, nuts and seeds also contain many protease inhibitors, thus combining soy with these foods demands special attention in this regard. In the case of wheat and other cereal grains, it is not advised.
Conclusion
Soy is a highly nutritious food, containing many compounds that have proven beneficial for health. Statements regarding the potential negative effects of soy products have been largely false when applied to healthy individuals. Just like any food, soy has some contraindications, most of which are rare and apply to specific states of disease. While soy-based preparations can benefit infants from a protein standpoint, it is not advised during these sensitive developmental years.
These concerns aside, the majority of people that consume it in moderation will only benefit. The proteins and nutrients in soy are known to improve cardiovascular health, lipid profile, lower inflammation, enhance mood, and support cognition. Lastly, soy products are not a substitute for a healthy diet overall and should be moderated within the context of a healthy, nutritionally-balanced diet plan.
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