Opinions on whether soy is a healthy addition to the diet are very split. Even within the medical and naturopathic world, colleagues often disagree as to whether soy should be included in the diets of men or women with a history of estrogen positive breast cancer. There is currently a huge arrangement of soy products available including miso, tofu, tempeh, soy beans (edamame), soy flour, soy milk, soy yoghurt and even soy cheese. Whether these products are beneficial or detrimental to health is dependant on many factors.

Traditional Asian cultures that regularly eat fermented soy products show lower incidence of hormonally derived cancers and cardiovascular disease. These epidemiological findings have prompted clinical trials to try and understand why.

Amongst other ingredients soy contains active constituents such as phytoestrogens and genistein. It’s the phytoestrogen component of soy which triggers the most debate. Phytoestrogens are plant based chemicals which behave similarly to estrogen in the body as they appear to compete with estrogen for the same receptor sites. Therefore if there is an otherwise low level of estrogen in the body and phytoestrogens are present, it is proposed that they fill otherwise empty estrogen receptor sites and have an estrogen like affect in the body. 

It is proposed that phytoestrogens are ‘trophorestorative’ or have a ‘normalising’ or balancing effect of estrogen in the body. Even though there is an estrogen-like effect, phytoestrogens are not as strong as estrogens produced in the body. Therefore phytoestrogens can also have an estrogen lowering effect in the body if the weaker phytoestrogens occupy the receptor sites of the otherwise stronger estrogen. 

A number of studies have indicated that the consumption of phytoestrogens during the menopausal phase can improve symptoms such as hot flushes and vaginal dryness. It is important to acknowledge that food intake may require consistent consumption over a number of weeks or even months before results are observed, as it is a more gradual, building up approach rather than taking a quick fix (and possibly temporary fix ) pill. 1-2 tbl per day of freshly ground flaxseeds has been shown to improve symptoms of menopause. Flaxseeds contain isoflavones – a particularly beneficial phytoestrogen. There is also promising data suggesting an intake of soybean phytoestrogens (in particular the isoflavones) may be beneficial to maintain good long term bone density which can potentially become a health issue after menopause. 

There are also other sources of isoflavone phytoestrogens which are not soy derivatives such as the previously mentioned flaxseed, red clover, chickpeas, kidney beans, lima beans and parsley which may be nice inclusions to the diet of menopausal women if they can’t tolerate soy.

The phytoestrogen effect of soy contributes to one particular debate suggesting that if males consume soy, it will have an estrogenic or feminising effect on their hormonal status. This has not been scientifically verified. 

One of the other debates surrounding soy products is the potential impact on thyroid function. Soybeans contain chemicals called phytates which bind to minerals such as iron, zinc and iodine, and may potentially reduce the absorption of these nutrients in the body. There is particular question regarding the impact of consuming soy products and the interference with healthy thyroid function. Some health professionals recommend that people with hypothyroidism (underactive thyroid) are better to avoid soy products as some people have experienced a slightly inhibitory effect on thyroid function. The traditional fermented soy may be less of an issue and therefore the better choice if required rather than the highly processed options.

Men who regularly eat soy in their diet are shown to have a lower incidence of prostate cancer. One of the contributing factors to prostate cancer is an unhealthy derivative of testosterone called dihydrotestosterone (DHT), and soy has been shown to decrease the production of DHT. Therapeutic doses of zinc are also important to include in the diet of men with incidence of prostate cancer, or indeed to contribute as a protective nutrient.

There are some studies suggesting that consuming soy products may improve cardiovascular disease parameters. Most notably the impact that soy may have in reducing total and LDL cholesterol levels.

Dr Lise Alschuler (a medical doctor and breast cancer survivor) presented research in 2012 confirming that women who had been diagnosed with breast cancer, whether taking tamoxifan or not, increased their survival rates and reduced their incidence of recurrence if they consumed soy phytoestrogens.  Chemicals called ‘indoles’ (found in broccoli, cauliflower, cabbage etc) have also been shown to beneficially regulate estrogen responsive activity by decreasing the levels of the unhealthy estrogen metabolite (16alpha-hydroxyestrone) which is associated with increased reproductive cancer risk in females.

It is however very important to ascertain the best version of soy to consume. As with food generally, any GMO (genetically modified organism) soy products are best avoided and relying primarily on the traditional fermented versions of soy such as miso, tempeh, natto, tofu and beans is recommended. The more processed the soy, the less likely it is to be a healthy addition to the diet. An organic, non-genetically modified soy milk although somewhat processed has been shown to be beneficial to health. The more processed versions such as soy yoghurt and soy cheese are less likely to be beneficial. Always choose products from the fresh/refrigerated section as opposed to the long life options which are usually stored in aluminium lined containers. 

Unfortunately soy has also made the list for potential high allergens. Many people with a dairy intolerance turn to soy as an option however find that they are also intolerant to soy. For those that are dairy and soy intolerant, other options such as almond milk or rice milk can be used.