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Is soy a healthy product or a hormone disruptor? Beneficial or risky?
The intake of plant- based diets has increased over the years, in part because of the supposed positive health effects compared to animal- based diets (How bad is eating meat?), and for environmental- related reasons. On the other hand, it is also supposed that plant products such as soy can cause hormone disruptions and other health risks such as cancer.[1] In this article we dive into health effects of plant- based products and in particular of soy. To soy or not to soy?
Our environment affects our health
Our environment affects our health in multiple ways. For example, when there are many fast food restaurants in the neighborhood (the physical environment), people are more likely to eat unhealthily. Or when friends and family (the social- cultural environment) are meat eaters and roast a pig every weekend, people are less likely to adopt a plant- based diet.
Food is also subject to the economic and political environment. For example national and international legislation regulates food safety. Some substances are allowed for human consumption and others are not because of adverse health effects. One example is legislation on Endocrine Disrupting Chemicals. These chemicals can disrupt human hormone system and can have adverse health effects. These chemicals are present in natural products such as in soy, and in human-made products such as in plastic.
Endocrine-disrupting chemicals
Endocrine-disrupting chemicals (EDCs) are human-made and natural chemicals that interfere with the body’s hormones. EDC’s can act in various ways in different parts of the body. They can:
- Mimic, or partly mimic, naturally occurring hormones in the body like estrogens, androgens, and thyroid hormones, potentially leading to hormone overstimulation;
- Bind to a receptor within a cell and block the naturally occurring hormone from performing. Examples of chemicals that block hormones are anti-estrogens and anti-androgens;
- Interfere or block the way natural hormones, or their receptors, are made or handled in the body, for example, by altering their metabolism in the liver.
Human- made hormone disruptors: Bisphenol A
One of the most common human- made endocrine disrupting chemical is Bisphenol A (BPA). This chemical is present in everyday products such as your plastic water bottle, food container, cosmetics and the receipt of your groceries. BPA is linked to adverse health effects such as weakening of immune system, hormonal disbalance and fertility problems in men and women, and early menopause. (How your everyday products can make you sick)
Natural hormone disruptors: Phyto- estrogens and soy
One of the most common natural endocrine disrupting chemicals are phyto-oestrogens, such as in soy. Natural EDC’s are naturally occurring substances with hormone-like activity found in some plants. Phyto- oestrogens are often linked to positive health effects but also to adverse effects.[2]
Phyto- oestrogens
What it is
Phyto- estrogens, also known as dietary estrogens, are naturally occurring substances with hormone-like activity found in plants. These substances have the structural similarity of endogenous human hormones with estrogenic activity and have the ability to mimic or interfere in the action of endogenous estrogens. Estrogens are essential for numerous processes in the body for example for reproductive processes, cardiovascular and metabolic systems and brain functioning.[3]
How it works
Phyto-estrogens are able to bind with receptors of estrogen and therefore have the potential to affect all processes influenced by estrogen such as reproductive processes, cardiovascular and musculoskeletal systems and brain functioning and central nervous system.[4]
Not all the biological effects of phyto- estrogens involve estrogen receptors. They can also activate other hormone receptors such as those of serotonin, insulin and those involved in immune system. Therefore, it is proposed that phyto- estrogens can effect multiple processes of the body.[5]
Phyto-estrogen products
Phyto- estrogens are found in over 300 different plant species and can be ingested in the diet through the consumption of plant- based products.[6]
Phyto- estrogens can be divided into four groups: Isoflavones found in soybeans, legumes, lentils and chickpeas; coumestans found in young sprouting legumes, clover, and alfalfa sprouts; lignans found in cereals, linseed, flaxseed, fruits, and vegetables; and stilbenes found in grapes and peanuts. A single dietary source often contains more than one group of phyto- estrogens and not all groups have the same estrogenic effect. The most widely studied group of phyto-estrogens are isoflavones, found in soy.[7]
Soy
Soy contains a high concentration of isoflavones, the group of phyto-estrogens similar in function to human estrogen but with a weaker effect. Soy isoflavones can bind to estrogen receptors in the body and can cause weak estrogenic or weak anti-estrogenic activity.
Soy foods are rich in nutrients such as B vitamins, fiber, potassium, magnesium, and high-quality protein. Compared to other plant- based sources, soy protein is a complete protein. Soy contains all nine essential amino acids that the body cannot make which must be obtained from the diet. (Animal or Plant- based protein, which is better?).[8]
Health effects of phyto- estrogens
For many people, natural and plant- based products are instinctively healthier than artificial and animal- based products. Whether this is justified cannot be stated with certainty based on scientific research. However, this assumption can lead to unjustified or unsubstantiated attribution of positive properties to plant- based or natural products or overestimation of properties and downplaying of negative effects.
Unique individual response to soy
Research suggests that phyto- estreogens such as soy may have an effect on hormones and health, although the results are unclear ,as explained later. Soy phyto- estrogens can behave as an estrogen, androgen, or progestin, or have no effect at all. The effects of dietary phyto- estrogens on the body depend on numerous factors such as the phyto- estrogen type (group); the combination with other foods it is eaten with; and the health status of the consumer. For example, how the body responses to soy depends on:
- The type of soy product eaten
Is it a whole soy product such as tempeh, a processed soy product such as a veggie burger, how is the product stored; is it a fermented version (it seems fermenting soy increases its digestibility and absorption) or a liquid version (liquid food is absorbed faster than solid food)?
- How well the body can absorb soy
Only 30to 50% of people have specific gut bacteria that can process soy isoflavones into compounds with esterogen- like effects. This percentage is higher amongst Asian populations (Your poop tells it all). Race, genetics and composition of the gut are relevant. People of Asian race can convert these substances better than the Western population. (How your genes determine what your best diet is).
- Current hormone levels
Premenopausal women have much higher estradiol levels compared to post- menopausal women, and as a result they respond differently to soy.[9]
Inconclusive results
Research results on the health effects of phyto- estrogens and soy are not fully conclusive and results are sometimes conflicting. According to some soy is not the healthiest, according to others it is. Some researchers suggest that phyto- estrogens may lower the risk of osteoporosis, cardiometabolic diseases, cognitive dysfunction, cancer, and menopausal symptoms, and the consumption of phyto- estrogens such as soy could be helpful in the prevention and treatment of several diseases. However, other researchers describe phyto- estrogens as endocrine disruptors and believe their beneficial effects are overestimated. [10]
This apparent disagreement could be partially due to the variability and incomparability of studies. For example, studies examine different types of soy products; studies are conducted among different groups of people with different hormonal status; or studies are conducted on animals and finding may not be applicable to human.[11] Much research has been done on the impact of phyto- estrogens and soy on a number of health conditions, as discussed below:
Phyto- estrogens and chronic diseases
Research shows a lower incidence of chronic diseases in East Asian people who consume soy, compared to Western populations who experience more chronic disease and eat less soy. The strength of the presumed association between soy and a lower incidence of chronic diseases is unclear.[12]
Phyto- estrogens and menopause
There are mixed results on the effects of phyto- estrogens and soy on menopausal women. Some studies report indications that isoflavones intake can help to reduce menopausal symptoms caused by a decrease in the production of endogenous estrogen, such as hot flashes, mood swings and fatigue and can help to lower blood pressure, even accounting for placebo effect.
Some studies claim that soy isoflavone supplements, derived by extraction or chemical synthesis, are significantly more effective than placebo in reducing the frequency and severity of hot flashes. Some studies claim 100mg of isoflavones per day in post- menopausal women can reduce menopausal symptoms, with less health risks regarding breast, endometrium and the risk of blood clotting compared to hormone replacement therapy.
Some studies report beneficial health outcomes but also mention it is too difficult to come to conclusions considering the lack of standardized research protocols.
Other studies refer to placebo- effects.[13]
Regarding post- menopausal women, numerous studies report that phyto- estrogens do not affect estrogen or progesterone concentrations Reported effects may be due to genes that influence diet effects.[14]
Phyto- estrogens and cancer
The use of isoflavones since adolescence is associated with a reduced risk of breast cancer compared to this risk with hormone replacement therapy. There are also studies showing an association between phyto- estrogens and an increased risk of breast cancer.
Research on the protective effect of phyto- estrogens on endometrial, ovarian and prostate cancer is inconclusive. Some studies suggest isoflavones are associated with an increased risk, others with a reduced risk. Research results may be conflicting partially due to factors such as dose, type, bioavailability, and current hormone levels of the consumer.[15]
Phyto- estrogens and bone health
Research results on the effects of dietary phyto- estrogen on bone health in premenopausal women are inconsistent.
In menopausal women the decrease of estrogen increases the risk osteoporosis. It seems the intake of isoflavones can help prevent bone loss in both menopausal and post- menopausal women. Although other studies mention that the efficacy of isoflavones such as in soy has not been proven.[16]
Phyto- estrogens and cardiometabolic health
Risk factors for cardiometabolic diseases are high blood pressure; obesity and low grade inflammation in fat tissue; diabetes type 2 and insulin resistance; and stress and high cortisol levels. Research on the impact of phyto- estrogens on cardiometabolic health seems inconclusive.
Some studies show the intake of phyto- estrogens is associated with a decrease in blood pressure, but do not show any effect on insulin levels. Other studies show the intake of phyto-estrogens is associated with both an increase and a decrease in insulin sensitivity.
Some studies show the intake of phyto- estrogen in obese post- menopausal women does not change hormone levels, but they report a decrease in insulin resistance in diabetic women who consume soy. No significant changes in cortisol are seen in healthy women or in those at cardiometabolic risk after consuming soy isoflavones.
There are studies showing phyto- estrogens can reduce total cholesterol and improve heart function, and isoflavones can reduce hypertension. There are also indications that eating more than 25 grams of a soy product every day can help to lower blood pressure during menopausal transition. But, the results on the effect of the intake of isoflavones alone seem inconclusive. [17]
Phyto- estrogens and diabetes
The intake of isoflavones seems associated with al ower risk of developing diabetes type 2, although the association between the intake of phyto- estrogens and insulin sensitivity is inconclusive as mentioned previously.[18]
Phyto- estrogens and inflammation/ immune system
Inflammation is related to an increased risk of cardiometabolic diseases such as stoke, cancer, and diabetes type 2. Research on the positive effect of isoflavones intake on inflammation are conducted on animals and show an anti- inflammatory effect. Furthermore, research shows phyto- estrogens might suppress the immune response.[19]
Phyto- estrogens and weight loss
Research shows phyto- estrogens can increase fat-free mass and reduce fat accumulation. Long-term isoflavone supplementation also seems to reduce visceral fat tissue, related to the risk of chronic disease such as obesity, diabetes type 2 and cardiovascular disease. [20]
Phyto- estrogens and brain function
Some research shows a positive influence of phyto- estrogens on cognitive brain function. Some studies report that younger post- menopausal women might derive more than older women on cognitive benefit from isoflavone therapy. [21]
Phyto- estrogens and skin health
Phyto- estrogens seem to be able to act as anti- aging in the skin. [22]
Health risks of phyto- estrogens
Concerns about the health risks of phyto- estrogens, and in particular of soy, are often based on the results of animal studies. It seems human research supports the safety and benefits of soy. Nevertheless, there are some indications of possible risks, discussed below.[23]
Phyto- estrogens and interference with current hormone levels
It seems uncertain if a phyto-estrogen-rich diet can trigger an imbalance of estrogen and progesterone concentrations or if it can affect thyroid hormone levels. Research shows that in women phyto-estrogens could disrupt the endocrine system by interfering with the hypothalamic–pituitary–gonadal axis, which controls estrogen secretion. Phyto- estrogens also seem to inhibit the synthesis of steroid hormones.
Some research shows a significant decrease in estrogen levels after the consumption of soy products in premenopausal women. As well as a decline in estrogens, a significant decrease in progesterone levels after phyto- estrogen consumption has been observed. Other studies do not report any modifications of sex hormones related to the consumption of soy.
In men, the influence of isoflavones on testosterone levels is inconclusive.
According to the European Food Safety Authority isoflavones do not adversely affect the breast, thyroid or uterus of post- menopausal women.[24]
Phyto- estrogens and pregnancy
The impact of phyto- estrogens on human development is not clear. It seems phyto- estrogens can have both beneficial and adverse effects. Some animal research shows that phyto- estrogens have the potential to act as endocrine disrupters during reproductive tract development in males and females and that phyto- estrogens could interfere with reproduction. The Dutch Health Council advices women to avoid phyto- estrogens (soy) before and during pregnancy.[25]
Phyto- estrogens and disease
Research links a higher than average intake of soy to an increased risk of Kawasaki disease (a disease mainly affecting young children). [26]
Phyto- estrogens and interference with medication
Isoflavones can interfere with certain medication such as for cysticfibrosis, kidney stones and hyperthyroidism.[27]
Phyto- estrogens and allergies/ side effects
Some people are allergic to soy. Others experience digestive problems and sleepiness after eating soy. It seems these side effects are more common in women over the age of 55, also Asian studies show higher rates than Western studies. [28]
The Dutch government agency responsible for registering adverse side effects to products reported 67 cases of adverse reactions to phyto- estrogens. These appear to be most frequently on silvercress (47.8%), hops (32.8%) and soy bean (22.4%). In the international VigiBase database with a total of 21,944 reports, this is soybean (71.4%), silvercress (11.6%) and Monk's pepper (6.4%). The side effects reported are mainly gastrointestinal complaints, skin complaints and symptoms such as vaginal bleeding and swollen breasts.[29]
Conclusion and Advice
To soy or not to soy?
Safe and no- regret
Soy and its estrogenic and anti-estrogenic effects on the body are widely studied. Results of recent population studies suggest that soy has either a beneficial or neutral effect on several health conditions. Soy is considered a safe source of protein for a healthy adult who does not deal with underlying medical conditions or pregnancy. It can be eaten several times per week and provides health benefits compared to eating red and processed meat as a protein source. (How bad is eating meat?)
Isoflavones dietary supplements are still under research. Eating a moderate amount of isoflavone-containing whole foods seems to be the safest.
Intake recommendation
There are only a few soy intake recommendations from independent health organizations, and its value depends on the underlying assumptions. For example, one basis for formulating an intake recommendation is to mimic the intake of regions that have traditionally consumed soy foods such as in Asia. Obviously, this may not represent optimal intake. Another basis is to consider the intakes associated with desirable health outcomes in observational studies or clinical trials.
According to the current state of science, the adult intake recommendation is 15–25 grams of soy protein per day, and 50 to 100 mg of isoflavones per day. (The amount of isoflavones needed to give health effects is around 40-70 mg/day or an average of 50 mg/day, depending on how well it is absorped).
Consuming amounts that exceed these recommendations is not associated with adverse effects. Nevertheless, given the dietetic principles of moderation and variation, and the benefit from consuming nutrients provided by other dietary sources of protein, it is reasonable to recommend that soy protein not account for more than 25 to 30% of total daily protein intake.
The average daily intake of phyto- estrogens in Asia is estimated to be between 20-50 mg per day. In the U.S. this is 0.15-3 mg per day, and in Europe around 0.49 to 0.66 mg per day. The average consumption of isoflavones in Asian society is 15-50 mg per day, while in Western countries only about 2 mg per day.[30]
The table below gives an indication of the content of plant- based products.[31]
Create your own health!©
References
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[16] Alexander V. Sirotkin, AbdelHalim Harrath, Phytoestrogens and their effects, European Journal ofPharmacology, Volume 741, 2014, Pages 230-236, ISSN 0014-2999, https://doi.org/10.1016/j.ejphar.2014.07.057.;Domínguez-López I,Yago-Aragón M, Salas-Huetos A, Tresserra-Rimbau A, Hurtado-Barroso S. Effectsof Dietary Phytoestrogens on Hormones throughout a Human Lifespan: A Review. Nutrients. 2020; 12(8):2456. https://doi.org/10.3390/nu12082456.;Michelle Mostrom, Timothy J. Evans, in Reproductive and Developmental Toxicology, 2011.Retrieved April 2024 via: https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/phytoestrogen.; NorthAmerican Menopause Society. The role of soy isoflavones in menopausal health:report of The North American Menopause Society/Wulf H. Utian TranslationalScience Symposium in Chicago, IL (October 2010). Menopause. 2011Jul;18(7):732-53. doi: 10.1097/gme.0b013e31821fc8e0. PMID: 21685820.; ZOE. Isoflavones and their healtheffects. Retrieved April 2024 via: https://zoe.com/learn/isoflavones.
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