Soy - Fab or Fad?

Soybeans have been used in parts of Asia for thousands of years. The first foods made from the legume were products of fermentation, including miso, soy sauce and tofu. Soy was introduced in the West in the 17th century, when soy sauce became a popular item in East-West trade.

Today soybeans are also used to make a wide range of food and drinks offering a protein-rich alternative to dairy products and meat, including soy flour, grits, textured vegetable protein, yoghurt and milk. Soybeans and whole soy foods are high in fibre and have a low glycemic index (GI). They are low in saturated fat, contain no cholesterol, are a source of omega-3 fatty acids, and contain minerals and vitamins, including some B-vitamins, zinc, potassium and magnesium.

Soy is also one of only two known plant foods that contain all the essential amino acids, similar to those in meat, so it’s a good substitute for animal proteins. The Dietitians Association of Australia recommends including soy foods as part of a healthy eating plan.

The case for soy

Some formal medical studies have reported various health benefits of consuming whole soy foods, including lowered blood pressure, reduced risk of osteoporosis and cardiovascular disease, and management of endometriosis.

Also, it seems a soy-rich diet may help to reduce menopausal symptoms such as hot flushes. Soy is high in phytoestrogens, also known as isoflavones, which are compounds that can bind to the body’s oestrogen receptors. Depending on the physiological environment, these compounds may exert either oestrogenic or anti-oestrogenic effects on the cells. It is thought that in menopausal women, the phytoestrogens provided by a soy-rich diet act like a mild form of hormone-replacement therapy.

Lower rates of breast and prostate cancers in some Asian countries have led scientists to investigate a possible link between eating soy foods and protection against these forms of cancer. Overall, in large studies, the results support the theory that a high consumption of soy foods may lower the risk of breast and prostate cancers. However, the Cancer Council Australia points out that it’s important to remember people in these countries may have different risks for these cancers because of genetic factors, and their overall diets differ from ours too – e.g. they eat more vegies and fish, and less meat.

So far, most soy research has focused on the protein and phytoestrogen content of the bean; soybeans are comprised of many additional nutrients, and some researchers believe it is a combined action of all these components that are responsible for the benefits.

Many experts agree that further research is required before the health benefits of soybeans will be conclusively understood.

...and the case against

There is evidence that soy may adversely affect thyroid function in some people – soy is a mild goitrogen, which means it inhibits the uptake of iodine necessary for thyroid function. Also, soy-based foods contain high levels of oxalate, a compound that can increase the risk of developing kidney stones in those who are susceptible.
Some animal studies have raised concerns that soy consumption may increase breast cancer risk. Scientists induced breast cancer in rats that had their own oestrogen removed; when the rats were given isoflavones, growth of oestrogen-sensitive tumours was accelerated. But, says Dr Peter Clifton from CSIRO’s Human Nutrition division, there’s no need for consumers to be concerned about eating normal soy-containing foods.

“Most soy products, whether it’s soy milk or soy burgers, usually contain very little of these isoflavones or phytoestrogens],” he says. “Most of the time, the processing of the soy removes the isoflavones.”

The Cancer Council’s view is that soy foods, like all legumes, can be beneficial as part of a healthy diet, provided they’re eaten in moderation. However it does not recommend the consumption of concentrated products like soy supplements (which may contain soy protein isolates) as a preventive measure for cancer, and also warns women who have, or have had, breast cancer to be cautious about consuming such products as high doses of soy could potentially interfere with some drug treatment, or may stimulate tumour growth.

Smart soy tips

• Eat soy as part of a healthy diet – for example, combine soy flour with wheat flour when baking, make sandwiches with soy bread, or add soybeans to casseroles. “Try adding tofu to a fresh green salad for lunch,” suggests Slimplicity Coach of the Year Dianne Webb from Fernwood, Petrie, Qld. “Eighty grams equals one serve of protein.”
• Check food labels – ensure products are made from whole soybeans, are low in sugar, and do not contain soy protein isolates (which are highly processed, refined and concentrated).
• Choose calcium-fortified soy milk and soy yoghurt – “If you heat soy milk before adding it to your coffee or tea, it won’t curdle,” says Dianne.
• For soy sauce, try tamari – it’s naturally fermented, made from whole soybeans and contains less salt than other soy sauces.
• Avoid soy supplements – they’re not a good alternative to eating whole food and contain high doses of isoflavones.

What about GM soy?

Soy products imported from the USA are the main source of genetically modified (GM) ingredients in food sold in Australia. GM soy is found not only in obvious soy products like soy flour, but can also be present in foods like chocolate, potato chips, mayonnaise and biscuits. If you’re worried about eating GM foods, check all product labels – food regulations require foods that contain GM ingredients to be labelled.