Soybeans and soy products (tofu, tempeh, soy drink and other soy foods) are the nutritional powerhouse of the legume family. A staple of Asian diets for thousands of years, they have long been a mainstay of vegetarian and vegan diets. They are an excellent source of protein, and rich in fibre, iron, zinc and B vitamins. They are lower in carbohydrate and higher in fat than other legumes, the majority of the fat is polyunsaturated.
On the whole, soy foods have not played a major role in the typical Western diet. In contrast, soy is regularly consumed by many Asians at all stages of life from weaning to old age. It’s this difference in levels of soy consumption that got the ball rolling in soy research says Dr Joanna McMillan. “Scientists found that levels of heart disease and many cancers, including breast cancer, were far lower in these soy-eating Asian countries, compared to levels in the West. Numerous studies followed to try to identify what it was about soy that might be protective,” she says.
“Research has centred on two aspects of soy – soy protein and compounds found in soy called isoflavones. Isoflavones are phytoestrogens (meaning ‘plant oestrogen’) and are similar in structure to the hormone oestrogen. These phytoestrogens can act in two ways:
- They can act like oestrogen. This may be beneficial during menopause for example, when natural oestrogen levels are dropping. Theoretically consuming sufficient phytoestrogens-rich soy at this time can reduce menopausal symptoms.
- They can block the action of oestrogen. This is potentially beneficial in for example breast tissue where oestrogen stimulates growth of both normal and cancerous cells. At least one of the isoflavones in soy, called genistein, has been shown in animal studies to inhibit the development of breast cancer.
Additionally, isoflavones have been shown to be powerful antioxidants and may in this way contribute to protection against diseases including cancer and heart disease,” says Dr Joanna. “However, I don’t recommend consumption of highly processed soy foods, such as those made from soy protein extract. Consuming these processed foods may have different effects to consuming the wholefood soy products traditional in Asia.” (see Read More below for the link in her blog on soybeans).