Nutrition profile of soy
Soybeans are members of the pea (legume) family of vegetables. Eating soybean-based foods may reduce the risk of a range of health problems, including coronary heart disease. More research is needed, but the evidence so far suggests that it is wise to include whole soy (or soya) foods in your daily diet.
Soybeans contain hormone-like substances called phytoestrogens that mimic the action of the hormone oestrogen. The health benefits of soy for menopausal women could include fewer hot flushes, protection from coronary heart disease (CHD) and lowered risk of osteoporosis.
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Soy is a high-quality protein. It is one of only two known plant foods (the other is amaranth seed) to contain all the essential amino acids, similar to those found in meat.
Some soy products are sources of calcium and iron, such as Chinese tofu or tempeh (made with a calcium coagulant) and calcium-fortified soy drinks. The soybean is:
- high in fibre
- high in protein
- low in saturated fat
- cholesterol free
- lactose free
- a good source of omega-3 fatty acids
- a source of antioxidants
- high in phytoestrogens.
The soybean needs further research before its health benefits are conclusively known.
Possible health benefits of whole soy foods not already mentioned include:
- lowered blood pressure
- improvements to blood vessels, such as greater elasticity of artery walls
- reduced risk of osteoporosis
- protection against various cancers, including those of the breast, colon, prostate and skin
- management of endometriosis
- anti-inflammatory effects.
Genetically modified soy products
Some people do not wish to eat genetically modified (GM) foods. Soy products imported from the United States are the main source of GM ingredients in food sold in Australia. Some soybean crops have been genetically modified to be resistant to herbicide, but they are otherwise identical to non-GM soybeans.
Genetically modified soy is found in primary soy products, such as tofu or soy flour, but it can also be found in a wide range of other foods such as chocolates, potato chips, margarine, mayonnaise, biscuits and bread. It is mandatory in Australia for foods to be labelled as ‘genetically modified’ if they consist of more than one per cent (by weight) of an approved GM ingredient.
Soybeans and coronary heart disease
Oestrogen may protect women against coronary heart disease (CHD) during their reproductive years, but rates of CHD increase remarkably after menopause. Soybeans have been shown to lower total cholesterol and LDL cholesterol levels, both known risk factors for CHD.
A meta-analysis (an analysis of multiple studies on a topic) of 41 clinical trials found that 20 g to 61 g of soy protein can significantly reduce total blood cholesterol levels, LDL (bad) cholesterol levels and triglycerides. The results also showed that soy protein supplementation slightly increased HDL (good) cholesterol levels. This amount of soy protein is found in two to three serves of soy products.
It is not known whether the phytoestrogens or the soy proteins (or both, working in combination) or the other characteristics of soy (including high-fibre content and low saturated-fat content) are responsible for these health benefits. However, studies have shown that eating soy protein without isoflavones results in only small cholesterol reductions and isoflavone supplements alone have minimal cholesterol lowering effects.
The cholesterol-lowering benefits of eating soy foods may be improved if the total diet is high in carbohydrate. This seems to help with the breakdown of the isoflavones.
Tips for increasing soy intake
If you want to increase your intake of soy:
- Choose whole soy foods like soy milk, soy yoghurt, soy bread and tofu.
- Check ingredient lists to make sure that the soy foods you buy are made from whole soybeans and not soy isolates.
- Make sure that products such as cereals contain soy protein and not just added isoflavone.
