HEALTH MYTHS ABOUT SOY: IS SOY GOOD FOR YOU? (PART 1)
Medically Reviewed by Dr. Rosmy Barrios - September 16, 2024
Soy is a widely consumed legume that originated in Asia and has been a staple part of oriental diets for thousands of years. During the course of the industrial era, soy has become a widespread food used as a common source of protein in many mass-produced goods. Due to its high protein content and flavor profile, soy products are among the most popular meat and dairy substitutes for vegetarians worldwide.
Over the last several decades, the use of soy in mass production has raised considerable doubt about whether soy is truly beneficial for health or not. Conflicting data has given rise to both skepticism and optimism regarding its properties. The following discussion aims to dispel a few myths that have plagued soy’s reputation and shed light on its optimal use as part of a healthy diet.
Nutritional Composition of Soy
The composition of soy has been studied in depth, particularly for mass food production.
Several soybean cultivars have been genetically modified to increase the yields of certain nutrients and enhance the production value of soy. As a result, different extractions of soy tend to retain different levels of nutrients compared to natural soybean cultivars and products.
Proteins
- Soy averages 24-36.49 grams of protein per 100 grams on average.
- Compared to other legumes, soy yields approximtly 50% more protein, even by comparison to green peas.
The protein content of soy mostly consists of glycinin and beta-conglycinin, which is known to be cross-reactive with casein. The proteins present in soy have proven to lower cholesterol, reduce inflammation, and stabilize blood sugar levels.[1]
The amino acid score of soy is nearly identical to that of beef on average, with slightly enhanced digestibility and better bioavailability. The protein quality of soy is similar to that of egg and milk, revealing that soy products are able to meet dietary protein requirements in a similar fashion.
Carbs
- Soy consists of 30.16 to 45 grams of carbohydrates per 100 grams on average.
- Approximately 9.3 to 100 grams of this constitutes fiber, while the rest consists of sugar.
- Soy has around 25-50% less carbohydrates than other legumes and less fiber.
- Processing, soaking or fermentation substantially lowers the carbohydrate content of soy.
The carbohydrate portion of soy contains several types of monosaccharides and polysaccharides. Monosaccharides are simple sugars that are quickly digested. Of these, soy includes small amounts of fructose, galactose, sucrose and glucose.
Polysaccharides are complex sugars that promote the health of the microbiome. Raffinose and stachyose are the main polysaccharides in soy, both of which are associated with improved gut health as well as digestive trouble in sensitive individuals.
In spite of increasing flatulence and potential discomfort, the health benefits of these complex sugars suggest that they may reduce the incidence of gut lesion formation and inflammation. Increases in beneficial bacteria such as Lactobacillus, Bifidobacterium, and Akkermansia species were noted in response to these two sugars.[2] [3] Furthermore, they are associated with reducing the risk of cancer, improving immune function, and improving mineral absorption.[4]
Micronutrients
The micronutrients in soy vary depending on processing methods. Traditional fermented soy products increase the content and quality of micronutrients, improving their absorption in the gut.
Soy micronutrients consist of:
Trace Minerals. Like all legumes, soy contains decent amounts of essential trace minerals, including calcium, zinc, phosphorus, potassium, iron, and magnesium. Of these, soy contains almost double the amount of calcium, magnesium, and iron compared to many other bean varieties. While not at the highest end of the spectrum, potassium and phosphorus levels are noteworthy in soy.
Vitamins. As with most legumes, the levels of vitamins are very low. Nonetheless, soy contains quite a high trace amount of vitamin K comparatively and minimal levels of B vitamins (B1, B2, B3, B6).
Saponins. Soy consists of roughly 0.17-6.16% saponins, which are known to possess health promoting effects. These include lowering inflammation, reducing cancer risk, inhibiting a variety of harmful microbes, and being both heart and liver protective.[5] The bioavailability of these compounds is very low and may be increased with dietary fats and fermented soy products[6].
Isoflavones. Isoflavones are a type of plant-based chemical that resemble estrogens, known as phytoestrogens. Soy contains roughly 1.2-4.2mg per gram of isoflavone when dry, however the content varies greatly across soy products[7]. They have been researched in depth for their health promoting properties. Due to their hormonal effects, there has been much debate over whether they are suitable for everyone. Isoflavones are discussed in more detail in the next section (see 7 Myths about soy that proved untrue).
Fats in Soy
- Soy consists of roughly 19.94-31 grams of fat per 100 grams.
- The PUFA content of soy is approximately 11.255 grams per 100 grams.
- Soy comprises of roughly 300 micrograms per gram of Vitamin E, making up roughly 1.5% of the oil component.
- Most of the isoflavone content is found in the fatty component of soybeans.
A rough indication of specific fatty acids found in soy is as follows:
- Palmitic acid 10% (Long chain saturated fat)
- Stearic acid 4% (Long chain saturated fat)
- Oleic acid 18% (Omega-9 fat)
- Linoleic acid 55% (Omega-6 fat)
- Linolenic acid 13% (Omega-3 fat, a portion of which constitute gamma-linolenic acid, an omega-6 fat)
All the above amounts refer to the raw soybean. Most of the fats in soy are lost or altered during processing, as a result of heat. After heating, the oils in soy become partially hydrogenated, increasing the relative quantity of oleic and stearic acids.[8] Out of all the fats present in soy, the content of polyunsaturated fats drops from 56% to less than 18% during the heat-processing. Any remaining polyunsaturated fats typically oxidize, becoming rancid quickly and leading to a shorter shelf life.
Genetic modification of soy grown for the oil is aimed at increasing the quantities of oleic and stearic acids, while reducing the quantities of linolenic acid. This modification ensures a longer shelf-life and better product stability. Products higher in oleic acid are healthier for the heart, while those higher in stearic acid are best utilized in cosmetic products.
Even after processing, the level of omega-6 fats in soy is much higher than omega-3 fats. This indicates that the fat portion of soy may predispose individuals to obesity and vascular inflammation[9], unless consumed in tandem with other sources of omega-3 to balance the ratio. A small portion of the omega-6 fats in soy consists of heart-healthy gamma-linolenic acid, which would serve to offset the negative aspect of this ratio.
Studies on soybean oil are contradictory. Some sources indicate that soybean oil reduces cholesterol and does not promote vascular inflammation. Other sources suggest that soy is healthier in this respect than palm oil[10], yet more adverse than coconut oil or fructose[11].
7 Myths about Soy that Proved Untrue
The following 7 statements about soy have elicited caution regarding soy consumption amongst health enthusiasts globally. Through careful examination of the evidence, it has become clear that these claims have likely been overstated.
1. Eating Soy Promotes Hormonal Problems
The main worry with consuming soy products would be endocrine disruption attributed to the consumption of isoflavones.
Isoflavones are phytochemicals (plant-based nutrients) that are known to have both estrogenic and anti-estrogenic properties. These components of soy interact with estrogen receptors through their structural similarity to estradiol, either inhibiting or enhancing their activation.
In high concentrations, estradiol has been known to disrupt hormones in both men and women. However, many studies have proven that Isoflavones do not possess very strong estrogenic properties by comparison to endogenous estrogen[12]. Some sources indicate that Isoflavone’s action on estrogen receptors is roughly 100 times weaker than estradiol[13].
Moreover there are two estrogen receptors: alpha (ERa) and beta (ERb). Estradiol is a very potent activator of ERa. When overactive, this interaction leads to endocrine disruption in both men and women. ERb activation inhibits ERa activation, serving to regulate this endocrine pathway. Studies have proven that Isoflavones have a higher preference for ERb than ERa, indicating that they would be able to regulate the action of estrogen as opposed to disrupting it.
It ought to be noted that while soy is one of the richest sources, it’s not the only food that contains isoflavone. Other examples include cauliflower, broccoli, barley, fava beans, kudzu, lupine, and red clover.
2. Men Should Not Consume Soy
Fear of the estrogenic effects of soy has purported the idea that it is safer for women to consume it than men. While it is true that too little testosterone and/or too much estrogen can disrupt male reproductive function, soy does not possess enough of an estrogenic impact to castrate healthy men outright!
Most reports that reveal negative results of soy on male reproductive function are based on animal studies[14]. These studies highlight that soy can alter male reproductive function, either by itself or in combination with other endocrine disruptors. Human studies have not reported adverse effects in healthy subjects and when soy is consumed in moderation within the context of a balanced diet plan.
One study took a look at 99 subfertile males that consumed varying amounts of soy in their diets. Those that consumed a very high amount had roughly 41 million less sperm per ml than those that didn’t consume any soy at all.[15] The effects were most pronounced in overweight and obese men, in whom estrogen excess and testosterone depletion are already known to be common factors. Therefore, soy is unlikely the main culprit causing infertility but may contribute towards a pre-existing health problem in large quantities.
Healthy men produce roughly between 40 to 200 million sperm per ml of ejaculate[16]. Anything lower than that is considered subfertile. Therefore, men who have hormonal or reproductive issues with a low sperm count may want to cut soy out of their diet until the problem is corrected. Healthy men may experience a minor reduction in sperm count temporarily after ingesting large quantities of soy. However, in the long run, the effects are typically negligible.
3. Soy Causes Cancer
The main concern here is that soy could promote reproductive cancers in both men and women through its estrogenic effects, namely prostate and breast cancers. The vast majority of studies have shown that soy protects against a wide variety of cancers (both hormonal and non-hormonal cancers[17]) through multiple mechanisms.
General Anticancer Potential of Isoflavones
Isoflavone has been shown to possess potent antioxidant properties that can serve to reduce the risk of cancer through inhibiting inflammatory pathways (NFkB and Akt). Further anticancer benefits include promoting healthy apoptosis (cell death) and autophagy (cell repair), allowing for optimal cellular turnover.[18]
This data is confirmed in Asian populations that consume a lot of soy products and have a very low incidence of cancer, particularly breast and prostate cancer.
Breast Cancer
There is good evidence to prove that soy makes for a great complementary intervention for those with estrogen and progesterone negative cancers, particularly breast cancer. Very few studies suggest that soy Isoflavones may promote the growth of estrogen and progesterone receptor positive cancers[19]. Contrary to these observations, long-term, low-dose amounts of isoflavone inhibited the formation of estradiol-induced breast cancer in vitro.[20]
Furthermore, the fact that soy isoflavones inhibit tyrosine kinase (a chemodrug target) suggests that even if it promoted the growth of hormone-positive cancers in some rare instances, it would then serve to inhibit them later on in the process; thus cancelling out any supposed “deleterious” endocrine effects.
The elderly are at an increased risk of contracting cancer, partly owing to the higher number of senescent cells in the aging body. Soy isoflavone is being studied as a complementary intervention in order to enhance estrogen levels in postmenopausal women. The results have shown that soy improves the hormonal profile of postmenopausal women without promoting the incidence of breast cancer.
Prostate Cancer
Similarily, Isoflavones were shown to cause prostatic cancer cells to die off, as well as enlarged prostate cells. Soy products with a low isoflavone content did not target enlarged prostate cells, yet still promoted death in prostatic tumor cells in vitro[21]. This highlights that the proteins in soy, aside from isoflavones, also convey anticarcinogenic properties, as supported by multiple studies. Nevertheless, it is the isoflavone content that appears to be the most potent in this regard[22].
Other studies suggest that some soy foods including soy milk, miso and natto, did not affect the risk of prostate cancer either negatively or positively.[23] Soy proteins are structurally similar to the dairy protein casein, which is known to promote the growth of prostate cancer cells.[24] Therefore, men may wish to moderate the consumption of soy protein isolates.
4. Soy Promotes Bodily Inflammation and Allergy
Soy foods are routinely excluded from many health programs as they have been associated with inflammation and allergy. While it’s true that soy is a known allergen in sensitive individuals, it’s not guaranteed that all soy products will cause inflammation and allergic reactions.
Proteins in soy are known to cross-react specifically with casein, promoting allergy in those with casein intolerance. [25] However, intolerances are often changeable, depending on the genes, diet, and lifestyle of the individual.
Intolerance to a food generally means that the individual lacks an enzyme capable of digesting the food in question, resulting in gastric upset. After many decades of research, it is quite clear that human digestive enzymes are rather limited and that most of our digestive capacity rests with our gut microbes. Many food intolerances have been treated using probiotic and prebiotic foods that encourage a healthy balance of gut bacteria.
Regarding soy, it is now known that Asian populations that consume fermented soy products extensively maintain a microbiome capable of efficiently degrading and absorbing soy. This further enriches the capacity of these individuals to absorb soy Isoflavones, which have been garnering a reputation for being notoriously anti-inflammatory in non-allergic individuals. Animal studies have shown that other probiotic strains, such as lactobacillus rhamnosus, may lessen the consequences of soy-based allergic reactions.[26]
In a study on post-menopausal women aged 50-65, soy milk with added Isoflavones did not significantly affect markers of inflammation and may have helped to protect against DNA damage[27]. These women also conveyed higher B cell counts than the control group.
5. Soy products cause thyroid problems
Following on from the debate as to whether soy acts as an endocrine disruptor or not, there is conflicting evidence as to the impact of soy on thyroid function. Some studies indicate that long-term use of soy, particularly the isoflavone genistein, has the ability to increase thyroid stimulating hormone and potentially promote hypothyroidism onset[28]. The main mechanism of action is through the inhibition of tyrosine kinase[29], which is an essential enzyme required to utilize thyroid hormones, as well as the neurotransmitters dopamine and serotonin.
Hypothyroidism is known to diminish the production of reproductive hormones[30], such as estradiol in women and testosterone in men. Theoretically, this could increase the anti-estrogenic effects of soy in women and the pro-estrogenic effects of soy in men.
Nevertheless, this effect is minimal in most studies[31], with a more pronounced effect being noted with the intake of soy protein isolates and related products (e.g. soy milk). Asian populations that consume the highest amounts of soy products do appear to have an increase in thyroid problems compared to Western populations[32]; however this increase is minimal and has been noted to co-arise with other diseases that have an additive detrimental effect on thyroid function (e.g. diabetes[33], lymphocytic thyroiditis[34]).
Tyrosine kinase inhibitors also happen to be a prime class of chemodrug, used to prevent the growth and spread of tumors. Hypothyroidism is a well-known side effect of such drugs as well. Soy offers a very mild form of the same class of drugs and therefore can be used as an effective anticancer food when incorporated into a healthy diet and lifestyle that supports thyroidal function.
6. Vegetarians are undernourished on soy products
The classic argument against going vegetarian would be a lack of essential protein and B vitamins, especially vitamin B12.
Many vegetarians have taken to soy as their main source of protein, due to its similarity to meat products in terms of flavor and texture. Indeed, this similarity reflects in the protein composition of soy, which mirrors that of beef. Unlike most other plant-based proteins, soy contains all essential amino acids in decent quantities and is therefore a great option for substituting protein while on a plant-based diet.
In spite of its wonderful protein profile, soy does not compare with meat in terms of offering adequate vitamin B12. However, the concept of vitamin B nutrition has been evolving over the last several decades highlighting the role of the gut microbiome as a major source of B12 production. In spite of this, most vegetarians are noted to be deficient across studies. This can be a result of consuming unbalanced vegetarian diets that do not emphasize probiotic foods, prebiotic fibers, or a reduction in toxins (including pesticides) that may prevent a healthy gut ecology.
Fermented soy products, such as soy yoghurt[35] and tempeh[36], have been shown to possess a higher vitamin B12 content compared to other vegetarian products. Soy milk and other soy products are often fortified with B12 to compensate for the lack seen in vegetarian diets.[37]
NOTE: Research in this field is still relatively new and it is inconclusive as to whether the gut microbiome can produce enough B vitamins to sustain our nutritional requirements. If you are consuming a vegetarian diet, it’s best to monitor your B vitamin status to ensure adequate intake and to take a supplement if necessary.
7. Soy-Based Infant Formula Promotes Deformity
Animal studies highlight that severe endocrine disruption, particularly caused by hypothyroidism, is capable of delaying puberty and promoting developmental defects[38]. Exogenous estrogens in high quantities are also capable of causing developmental abnormalities, particularly in infants.[39] Soy formula used to feed animal offspring has been shown to promote these adverse effects.
In human follow-up studies, the majority of healthy infants supplementing with soy formula do not suffer any adverse effects. However, soy formula rich in isoflavone may pose risks in infantile development[40]. Furthermore, infants with pre-existing health conditions such as congenital hypothyroidism[41], fragile X syndrome[42], autism, epilepsy[43], or gastrointestinal issues are known to experience worsening symptoms linked to soy or cow milk formulations.
To Be Continued
Health benefits, safety, contraindications, and considerations regarding soy products are further detailed in part 2 of this discussion.
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