Soybean is the richest source of protein among plant sources. It contains around 35g of protein per 100g. It is said to be a complete protein as it has all 9 essential amino acids. It is also low on carbohydrates (12g/100g) and high in fibre (21g/100g). Then why is it that this superfood has become a topic of controversy in the recent times? Read to learn more about soy, its origin, uses, benefits and controversies surrounding it.
Soybean the “king of beans” serves as a key source of high quality protein among plant sources. Since the 1950s, global soybean production has increased 15 times over. The United States, Brazil, and Argentina together produce about 80% of the world’s soy. Soy which was traditionally consumed in Asian countries, is now consumed all over the world. It is very versatile and can be used to produce soy milk, tofu, tempeh, soy sauce, natto, soy chunks, etc. Soy and its benefits in chronic disease prevention have been researched upon for over 25 years now.
What is the connection between soy and Oestrogen?
Oestrogen is an important sex hormone, produced by the endocrine system, that is responsible for the development of female body and the secondary sexual characters. It is responsible for the growth of breasts, hips being wider in women than in men, regulation of menstrual cycle, among other functions. For this reason, it is termed as a “female sex hormone”. Men also have oestrogen receptors and oestrogen in their bodies but to a much lower extent compared to women.
Soy has a type of phytoestrogen called isoflavones (genistein and daidzein) that is similar to oestrogen in terms of chemical structure. Phytoestrogen can bind to oestrogen receptors in humans and can have a relatively weaker oestrogenic or anti-oestrogenic effect i.e. have an effect similar to but weaker than that of oestrogen or act against oestrogen. Due to this property of soy, it has become the topic of controversy with myths associating soy with disruptions in hormone levels in men, development of male breasts, etc. First let us look at the benefits of soy and then discuss the truth about these controversies.
Benefits of soy for women
- PCOS- Soy may be beneficial to women with Polycystic Ovarian Syndrome, commonly known as PCOS. It is a metabolic, endocrine and reproductive disorder seen in women of reproductive age. PCOS is characterized by a variety of signs and symptoms. Menstrual irregularities, obesity or excess androgen could be a sign of this disease. In a study that administered soy isoflavone to women with PCOS for a period of 12 weeks. Significant improvement was seen in insulin resistance, hormonal status, triglycerides level and biomarkers of oxidative stress in the women studied.
- Breast cancer– Oestrogen hormone stimulates the growth of secondary sexual characteristics including breasts in women. It also stimulates the growth of breast cancer cells. Some studies on soy consumption in women show a protective effect against breast cancer (due to the anti-oestrogenic effect of soy in premenopausal women).
- Menopause- It is a widespread belief that soy is beneficial to postmenopausal women and that the phytoestrogen in soy (which has weak oestrogenic effects in humans) helps in regulating oestrogen level after menopause as there is a decline in oestrogen production. Some studies have reported a reduction in the intensity and frequency of hot flashes during menopause in women given soy isoflavone supplements.
Other benefits of soy for all
- Cardiovascular diseases- Many studies have reported beneficial effects of the isoflavones in soy on blood pressure, glycemic control, obesity and inflammation. A study in which participants included soyfoods in their diet (total quantity corresponding to 30g/day protein) for 12 weeks, a significant improvement was observed in biomarkers associated with cardiovascular risk.
- Cholesterol- Soy protein has been proven to have a hypocholesterolemic effect in both normocholesterolemic and hypercholesterolemic people. It lowers LDL cholesterol level and is also associated with a significant decrease in the ratio of plasma LDL cholesterol to HDL cholesterol. Therefore, soyfoods are beneficial for lowering cholesterol levels.
Why men fear soy
It is a common misconception among men that eating soy-based foods will lead to lowered testosterone levels or gynecomastia which is the development of male breasts. This fear is rooted in the fact that soy contains phytoestrogen which is perceived as an equivalent of oestrogen, the “female hormone”. Therefore consuming soyfoods is associated with the fear of reduced masculinity in men. But studies conducted on humans have shown that this is not the case. The effect of eating soy in both groups were studied but there were no significant changes in Testosterone levels in men. Consumption of soybeans or soy-based products on a daily basis did not cause any compromise in the virility or reproductive health in men. Nor did it have any other feminizing effects on the men involved in the studies at an intake level that was equal to or even considerably higher than the amount typically consumed by Asians.
Soy and thyroid
Recent studies have found an association between soy and thyroid function. There is a lot of confusion surrounding this and whether consuming soybeans are safe or not as studies are yielding mixed results. Let’s take a look at the existing evidence we have so far.
Soy is suspected to interfere with thyroid function but in whom? Animal studies have shown that when animals with pre-existing compromised thyroid function (such as hypothyroidism) and/or low iodine intake consume soy foods, there could be some disruption in their thyroid function. The exact component in soy responsible for this goitrogenic effect is still unclear. However, studies done on humans have not observed the same effect and the result is still inconclusive as to whether people with impaired thyroid function should avoid soy. Therefore, it is suggested that people with an underactive thyroid and those taking thyroid medication consume soy with caution. It is advisable to get sufficient iodine through the diet if consuming soy products.
A healthy individual with an optimum thyroid function can consume soy products without any fear as long as the iodine intake is sufficient. It is important to meet your iodine requirement if you are consuming a lot of soy products.
- Effects of Soy Protein and Soybean Isoflavones on Thyroid Function in Healthy Adults and Hypothyroid Patients: A Review of the Relevant Literature
- Effects of soy isoflavones on estrogen and phytoestrogen metabolism in premenopausal women.
- Goitrogenic and estrogenic activity of soy isoflavones.
- Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence
- Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis.
- The Effects of Soy Isoflavones on Metabolic Status of Patients With Polycystic Ovary Syndrome.
- Effect of soy on metabolic syndrome and cardiovascular risk factors: a randomized controlled trial.