The great soy debate
Soy is possibly one of the most widely misunderstood foods around. In the late 80s and early 90s, soy products grew in popularity as a low-fat, high protein alternative to animal products. But soy’s main selling point was that it was consumed regularly by the people of Okinawa, Japan, which was home to some of the healthiest and longest living people on earth.
As time went on, concerns emerged about the effects of soy on the hormonal system. Soy beans contain natural hormone-like substances called isoflavones, which mimic oestrogen in the body. Studies indicated that soy could disrupt the hormonal system, with implications for breast cancer, the menstrual cycle and thyroid function. The current research is conflicting to say the least – with some recent studies showing that regular consumption of soy is protective of breast cancer, and studies on soy and cholesterol show mixed results.
Whether soy is harmful or healthful remains a devisive topic, but there are a few things to consider when deciding whether to include it in your diet:
The first thing to understand is that soy products fall into two groups: fermented and unfermented. Fermented products include miso, natto and tempeh, and this is the form of soy eaten traditionally in Japan. Unfermented soy makes up the majority of processed products consumed in the UK, such as soy milk and the textured soy protein found in soy mince and vegetarian sausages. Tofu comes in both fermented and unfermented forms, although unfermented is far more common on the shelves.
So what difference does fermenting make? Soybeans naturally contain some undesirable substances - phytic acid which blocks absorption of minerals, and enzyme inhibitors which interfere with digestion. The fermentation process breaks down and deactivates these substances, removing the negative effects. Another benefit of fermentation is that it produces large amounts of beneficial bacteria (probiotics) which benefit digestion, immunity and cholesterol levels. These bacteria also produce a particular form of vitamin K, which is important for bone and cardiovascular health. All of these health benefits are not present in the unfermented bean.
Another factor when choosing soy is the possibility of genetic modification. Most soy is imported, and even though some supermarkets have non-GM policies they are often unable to say exactly where their ingredients come from. Organic brands are guaranteed to be GM-free and so are the safest choice.
There is also confusion about the ideal amount of soy to eat – with some sources saying that the Japanese eat relatively small amounts while others claim the opposite. The average consumption in Okinawa is estimated to be around 12g soy protein per day (equivalent to about 100g soybean); however there are large differences in the amounts consumed across different areas of Japan. In general, fermented soy like miso is consumed in far smaller amounts than unfermented forms like textured soy protein. Given that even fermented soy contains hormone-mimicking isoflavones, eating large amounts may not be advisable for those with hormonal sensitivities.
Taking everything into account, it seems that the best way to enjoy the benefits of soy is with a small but regular consumption of organic, fermented products like natto, miso and tempeh.