Soy has been extensively flaunted as a 'miracle' food by many over recent times. While some have praised soy for its potential to reduce cholesterol and the risk of cardiovascular disease; others have asserted that soy can protect against certain cancers. Further still, soy products have been said to play a role in naturally alleviating menopausal symptoms, as well as reducing the risk of osteoporosis.
But what does the science say in regard to soy? Is it really a venerable super-food, or are the positive effects of eating it over-estimated and under-achieved? Moreover, do the potential risks of consuming soy outweigh the possible health benefits?
Dr Cassy Richmond discusses some of the latest soy information to help you decide whether it is wise to switch to soy milk once and for all.
What is soy?
Soy originally comes from the soya bean, which is a type of bean (legume) originally found in Asia but now also grown in many other places throughout the world. You have probably seen many soy-based foods at your local supermarket, such as soy milk, tofu (soybean curd), miso (soybean paste), and tempeh (fermented soybean).
What's all the fuss about?
There is little contention that soy foods contain several nutritional properties. For example, soy is a good source of dietary fibre, calcium and protein. In addition, soy is a source of plant sterols and isoflavones (which are plant-based hormones, with antioxidant properties). It is believed that these provide soy with many powerful health effects.
Soy and your heart
Over the past few decades, many studies have explored the effects of soy on blood cholesterol levels, and found that soy may reduce LDL cholesterol (the 'bad' cholesterol) by around five percent. Research has also shown that regular soy in the diet may help to lower blood pressure.
Moreover, a study conducted in Japan has found that women, who ate soy products more than five times a week, were 70 percent less likely to have a heart attack or stroke compared with those women who had a low soy intake.
Soy and menopause
Hot flushes are a well-characterised menopausal symptom that can be potentially embarrassing and debilitating. They occur in menopausal women when there is a drop in the production of certain female hormones, including oestrogen.
While as many as 80 percent of Western women experience hot flushes, this symptom only occurs in around 18 percent of Chinese women. It is believed that many Asian women are spared menopausal symptoms because they consume plentiful soy in their diets.
Soy is a rich source of phytoestrogens (which have oestrogen-like activity). In this regard, many women are choosing to trial soy foods as an alternative to hormone replacement therapy to treat their menopausal symptoms.
Soy and your bones
Studies have shown that oestrogen hormone is important for encouraging normal bone mass; and that women are at risk of bone loss and osteoporosis after menopause. However, a US study has shown that post-menopausal women, who consume soy each day, are less likely to have bone loss.
There is also some evidence to suggest that bone fracture risk is reduced in those post-menopausal women who regularly consume soy although more research is required in this area.
Soy and cancer risk
Population studies have shown that Asian women, who consume daily soy foods, also have low rates of breast cancer. This finding has prompted scientists to investigate whether there is a link between soy consumption and breast cancer protection.
While some animal studies indicate that frequent soy in the diet may have an anti-breast cancer effect, other studies suggest that the oestrogenic effect of soy may promote the development of certain breast cancers in some women.
According to Cancer Council NSW, this area requires further exploration. While moderate consumption of soy foods is unlikely to cause adverse effects in healthy women, it advisable for those with a history of breast cancer (particularly oestrogen receptor positive breast cancer) to discuss with their doctor whether soy consumption is safe for them.
To soy or not to soy?
Although soy has been hyped as a miracle food over the past decade, there has been a recent curtailing of this enthusiasm. While soy may have healthy effects for some, it may promote cancer development in a selection of others.
For the most part, however, it is believed that a moderate amount of soy in a well-balanced, varied diet is generally safe for healthy individuals and this may even confer some significant health benefits. Ah moderation... isn't it always key?