Depending on who you listen to, soy beans are either a superfood with the potential to save the world or a bulking agent which presents a hazard to public health that could be playing havoc with our hormones and increasing the risk of breast cancer. Read on for the low down on the humble legume...
Soya beans originated in East Asia and many of us probably first came across them in condiment form, as soy sauce has been a fixture of Chinese restaurants in the UK for decades. It is valued for its high levels of protein and fibre and is particularly useful to vegetarians and vegans. Soya spread is a popular alternative to butter or sunflower spread, while soya milk is used in place of cow's milk.
Soya beans are rarely eaten as a discrete component of a meal, but are used to create many other products – including tofu, textured vegetable protein, tempeh and miso. Soy is also increasingly used in other processed foods such as ready meals. The majority of the global soy crop (75 per cent according to the WWF) is actually used for animal feed, particularly for chickens and pigs, so we may be indirectly consuming soy when we enjoy a plate of eggs and bacon in the morning.
As mentioned above, soy has remarkably high levels of protein and fibre for a vegetable – on par with eggs or milk. It is 30 per cent carbohydrate, 20 per cent fat and a whopping 36 per cent protein. It is low in saturated fat and contains significant levels of essential omega 3 fatty acids.
Soya beans also contain calcium and chemicals called isoflavones, both of which are useful in building stronger bones. This makes it a good option for those at risk of osteoporosis and for post-menopausal women. Other valuable vitamins and minerals include iron, magnesium, potassium, vitamins B6, E, K and folate. It also has a low glycemic index – meaning that it can help keep blood sugar steady by releasing energy slowly. There is also some evidence that soy can help lower levels of LDL "bad" cholesterol and also reduce hot flushes – though it's only been shown to have a slight effect in both cases.
The above information makes soya sound like a wonder food, which it arguably is, but there have also been concerns about both its safety as a human food.
Much of the negative press for the bean has focused on a link between the above-mentioned isoflavones and hypothyroidism. The chemicals are known to be able to oestrogen receptors and affect thyroid response. Studies suggest that most people will be at no risk, but that those with mild hypothyroidism might wish to avoid soya products.
There have also been studies on the relationship between soya consumption and breast cancer. Some research suggests a mild correlation with lower risk, but it has also been claimed that those isoflavones can "turn on" receptors that encourage cell growth in breast cancer.
The evidence does not seem to support this, however experts are not recommending increasing soy consumption in order to prevent the disease and sufferers are often advised to moderate their consumption of soy products.
Soy production has become big business and – like the palm oil industry – some activists have come to see it as a blight. Production has more than doubled since the mid-1990s and planting has been expanding most rapidly in South America – and Brazil in particular.
The big majority of soya bean crops are crushed to produce meal for animals or oil, which has become almost ubiquitous in processed food in the US.
The World Wildlife Fund highlights several areas in South America which have borne the brunt of the soy explosion. These include the Amazon, where soy farmers are pushing cattle rancher further into the forest, and the Cerrado savannah which covers one quarter of Brazil and is now claimed to be disappearing faster than the Amazon. As a result campaigners have been pushing for tighter restrictions on the expansion of soy cultivation.