(Is soya bad or good for your hormones?)

One of the most popular wellness trends of the past year, which will only become more and more popular is a plant-based diet. Consuming primarily plant-based food promises you a healthier version of yourself and our planet. However, blindly following the mainstream without educating yourself first about the nutritional needs of your body can leave you with a greater chance of ending up consuming processed vegan products like soya meat.

Soy products are indeed one of the pillars of a modern plant-based diet. They are amazingly diverse, rich in protein and a seemingly ethical way to break up with the notorious livestock industry. Manufacturers have found a way to turn soy into milk, burgers, hot dogs, ice cream, yoghurt and more. Despite the accessibility and abundance of soy products, this food category remains highly controversial.

There are a few myths and accusations floating around soya: it can negatively affect the hormonal balance in both men and women or even provoke the development of cancerous tumours. Luckily, soy has been on the market for a while and it is one of the most studied plant foods in recent decades. A good number of reputable studies allow us to look at real data and disseminate some of the misconceptions.

Nutritionally speaking, soy is one of the few plant sources of complete protein and contains all the essential amino acids. In addition, soybeans are rich in vitamins B1, B2, B3, B5, B6, B9, and C, minerals (calcium, phosphate, magnesia, magnesium, potassium, and zinc), omega-3 and omega-6 essential fatty acids and many other phytonutrients.

One serving of soy is roughly equivalent to 1 cup soy milk or 1/2 cup tofu, tempeh, soybeans, or soy meat. This is about 8 to 10 g of soy protein and 25 mg of isoflavones.

 So where is the problem, you might ask? The root of the controversy around soy is the fact that it contains a uniquely high amount of isoflavones  - hormone-mimicking compounds.  These substances belong to the group of phytoestrogens and their structure is similar to the hormone oestrogen. Isoflavones can partially act like oestrogen, however, in a less targeted and active way. Nonetheless, if consumed in high concentrations, isoflavones can alter the natural hormonal balance.



Soy contains phytoestrogens or plant-derived oestrogens. They are naturally present in many other food groups in lower amounts, including lentils, oats, peanuts and beer. Phytoestrogens have been part of our traditional diet for a long time, so our bodies are adapted to them. Phytoestrogens can help regulate and metabolize estradiol – the strongest form of oestrogen. For example, phytoestrogens buffer oestrogen receptors and promote natural oestrogen detoxification. In the presence of high estradiol, phytoestrogens have a net antiestrogenic effect. They make women's cycles easier and improve symptoms of excess estrogen such as PMS and heavy periods. Phytoestrogens are also commonly prescribed as supplements during menopause to support a drop in hormones and naturally stimulate the activity of oestrogen receptors.  


The thyroid gland produces hormones such as triiodothyronine (T3) and thyroxine (T4), which regulate metabolism. Iodine is essential for the proper production of these hormones. Studies have shown that the isoflavones in soy can block thyroid peroxidase (TPO), an enzyme involved in the synthesis of thyroid hormones. However, this mostly occurs when the patient is deficient in iodine. Left unaddressed, this fact can lead to hypothyroidism and even an enlarged thyroid gland, known as a goitre (an overgrowth of the thyroid gland).

Almost anyone who has a reliable source of iodine in their diet (iodine is found in many plant foods, especially seaweed and iodized salt) can safely consume soy without the risk of thyroid problems.



Although the compounds in soy products have been compared to less active forms of female hormones, a meta-analysis based on more than 50 groups of men found that neither soy products nor soy isoflavone supplements in normal doses (less than 200 mg/day) had an effect on testosterone levels and may even help prevent prostate cancer. An analysis of studies published in the American Journal of Clinical Nutrition found that increased soy intake resulted in a 26% lower risk of prostate cancer. Some animal studies suggest that abnormally high levels of processed soy consumption (more than 12 portions per day) can affect male fertility, but this data can’t be applied to humans. More research is needed in this area to understand better the long-term effects of soy product consumption and isoflavones supplements.   



The vast majority of studies agree that soy is either harmful to or protective against breast cancer. These data mainly refer to soy consumption in amounts of two servings per day or less. In January 2008, researchers at the University of Southern California found that women who consumed an average of one cup of soy milk or half a glass of tofu daily had a 30% lower risk of developing breast cancer, compared with women who consumed less or no soy. However, women who are already diagnosed with breast cancer should consume soy with care as it may increase the activity of mutated receptors.



A 2009 meta-analysis found that women with higher soy intake (about one serving a day) had a reduced risk of endometrial and ovarian cancer compared to women with lower soy intake. Two other studies that lasted three years found that soy isoflavones at 70, 80 and 120 mg/day did not adversely affect the endometrium. However, one study using 90mg of isoflavones for five years (equivalent to 3.5 servings of soy per day) found endometrial cell growth (though not cancerous) in some subjects. Women at risk for endometrial cancer may need to be careful about eating more than one serving of soy per day. For the most part, research indicates that diets containing lower levels of soy, such as 1-2 servings per day (as part of a well-balanced diet), should not adversely affect ovarian function in terms of ovulation.

When we talk about the need for soy in general, it is important to remember the presence of diversity in the diet. Studies mostly agree that moderate soy consumption is safe unless you have a medical condition, which requires extra attention for hormone-mimicking compounds. Whether you follow an animal-based or plant-based diet, make sure you don’t overconsume any groups of products and maintain a healthy balance and diversity of nutrients on your plate.




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