Soy, scientific name glycine max, is a plant of the Leguminosae family like beans, peas or lentils. The fruit of the plant are pods that have inside the seeds, the soy beans that we commonly find on supermarket shelves either in dried form or, after a manufacturing process, in form of milk, tofu, yogurt, tempeh or miso. Soy has been studied in recent years to verify its health properties, let's try to understand better what science says about it.
Soybean, nutritional properties
What emerges from the scientific studies is that soy is a precious source of easily digestible proteins, fats, of which 90% unsaturated fats, both of the omega 6 and omega 3 type, while it provides few carbohydrates when compared to other legumes such as lentils or beans (Messina et al, Nutrients, 2016). Not only that, soy is also one of the most important sources of calcium, whose degree of absorption is comparable to that contained in cow's milk, iron, which, being in the form of ferritin, is absorbed by the body, potassium, magnesium and phosphorus. Also valuable the intake of vitamins of group B but also of vitamins E and K (Messina et al, Nutrients, 2016).
Soy and phytoestrogens, are they bad?
Soy also provides isoflavones, especially genistein. Isoflavones are antioxidant substances that have the characteristic of being structurally similar to the body's estrogens, and this is also the reason why they are called phytoestrogens. Phytoestrogens have been at the center of a long debate to evaluate their efficacy and safety, especially in menopause. However, EFSA, the European Food safety authority, has established, after a long and detailed study, that even in post menopause phytoestrogens do not cause problems on the breast, on the thyroid or on the uterus. The North American Menopause Society also concluded that isoflavones do not carry risks (Messina et al, Nutrients, 2016). Indeed, it seems that isoflavones are even beneficial and that they perform an anticancer action. In fact, among the people from countries where soy is eaten daily, and therefore the Asian countries, there are fewer cases of breast cancer than among people from the countries with a Western diet. As a proof of this, breast cancer has also increased in cases where, in Asian countries, people started to adapt to the typical Western diet. According to scientific studies, it seems that this protective effect of soy on the breast occurs especially when its consumption begins already in adolescence (Messina et al, Nutrients, 2016). As for those who have already been affected by this tumor, the position of the American Cancer society and the American Institute for Cancer reasearch is that soy and its isoflavones are not a risk, indeed, as reported by World Cancer Research Fund International, it seems that soybean consumption improves prognosis (Rizzo et al, Nutrients, 2018). For what concerns men, isoflavones have been shown not to alter testosterone values (Hamilton-Reeves et al, Fertil Steril, 2010).
Soy and heart health
Soy protein has a cholesterol lowering action and the American FDA, Food and Drug Administration, has established that 25 grams of soy per day is the minimum limit to have this effect. This threshold can be reached during the day by mixing soy products of different origins, therefore milk, yogurt, bread, tofu, just to mention a few examples. Not only that, soy also protects the heart with its hypotensive effect, reduces the stiffness of the artery wall and helps to reduce the risk of type 2 diabetes. However, in this case the mechanism is still poorly understood (Pabich et al, Nutrients, 2019).
Soybeans, contraindications and warnings
Soy is therefore a healthy food that, if possible, should be included daily in your diet. However, some precautions should be taken, especially if you are taking thyroid medications. In fact, soy could interfere with some drugs such as levothyroxine used in case of hypothyroidism (Messina et al, Nutrients, 2016). As for the type of soybean, it is preferable to choose non-GMO organic soybean, since no conclusion has yet been reached regarding the safety of the genetically modified product and more long-term studies are needed to get an idea (de Vendomois et al, Int J Biol Sci, 2010).