Are Soy Products Bad For Your Health?
What is it about soy that makes it so controversial? It's an important crop in the United States and enjoys a generally healthy reputation, less so in Britain.
Although soy has become more familiar here (soymilk sales have soared with increased adoption of free-from foods, and edamame beans are a staple of urbanites' takeaway lunchtime choices) there is more than a whiff of caution about it.
The original and populist view was that soy was involved in some forms of cancer, especially breast cancer, and so the early collective received wisdom was always to exclude it. This is largely outdated now yet still some of the bad reputation lingers.
And of course, nutrition isn't black and white. Although we might want to be told that we can or can't eat a food, things are rarely that simple.
The nutritional facts
But here's what we do know: soy is very much a wholefood as it ticks most nutritional boxes. It's a complete protein (containing all the amino acids necessary for the human diet), offering 36g per 100g along with 9g fibre plus omega 3 and 6 fatty acids and a wide range of minerals and vitamins. It is also remarkably versatile and can be consumed in many ways; aside from tofu and edamame, there's miso, tempeh, soy sauce, soy nuts, soy cheese, soy yogurt and soy milk. Soy is also used in various forms as a food additive, found in everything from stock cubes to chocolate so you may already be eating it more often that you think.
The hormone question
But the controversy surrounding its health claims are due to chemicals within soy which are similar to female hormones. Most legumes (foods like beans and pulses) contain plant compounds called isoflavones, although three types, diadzein, glycitein and genistein are especially concentrated in soy. The chemical structure of these specific isoflavones is coincidentally similar to that of oestrogen and as such they can mimic the effects of the hormone. Therefore it is possible that any health issues related to hormones can – in theory – be influenced by these substances in soy.
This is especially true of breast cancer, linked to the activity of oestrogen, which can prompt cancer cell proliferation in vulnerable tissue.
But while the action of the isoflavones is similar it is not identical to human oestrogen and this makes a big difference to the way tissue responds to the hormone. Breast tissue holds several receptors that interact with various forms of oestrogen, and it is the alpha-receptors that are most likely to be linked to cancerous cells. Oestradiol, the human form of the hormone, binds to both the alpha and beta type of receptors, whilst isoflavones, the plant version, bind to the beta-receptors that can, in turn, reduce the activity of the cancer-stimulating alpha-receptors. This was highlighted in a recent study which discovered soy is safe to eat, and might even be beneficial for breast cancer survivors.
So in broad terms, isoflavones can offer a degree of protection against breast cancer but there is a proviso. It seems that the protective potential comes from consuming isoflavones as part of the diet, not by taking them in isolation in supplement form. Furthermore the benefits of dietary isoflavones start in childhood as consuming soy in early life can help reduce the incidence of breast cancer later in life, even in post-menopausal women who are the most at-risk group (77% of breast cancer cases occur in women over 50).
Can soy be used as HRT?
Many symptoms associated with the dramatic drop in oestrogen during the menopause may in some cases be alleviated by dietary isoflavones, although, it seems, only to a small degree. Studies show that hot flashes, night sweats and mood swings can be reduced by isoflavones but it should be remembered that taking isoflavones in supplement form, such as in black cohosh and red clover, could have complications as aside from the temporary relief from symptoms. Studies show that one of the isoflavones, genistein, encouraged cancer cell proliferation in mice when administered in isolation so caution is advised.
But eating soy or any legume doesn't always mean that we can benefit as some populations process them more efficiently than others. It is estimated that people of Asian descent extract twice as much of the favourable isoflavones than white people although why this is so is not fully understood. It could be linked to gut bacteria.
Soy has health benefits in other areas too. For example, it offers a degree of protection against prostate cancer and can protect against cardiovascular disease partially by swapping animal protein for plant derived ones such as soy (leading to reduced overall cholesterol and triglycerides).
This may seem like a glowing reference for soy but of course that would be too simplistic. However, you needn't avoid the tofu unless, of course, you want to.