Soy and your health

By Meeghan, 26 February, 2012

The popularity of soy-foods in the Western world is on the rise, with new soy products popping up all over our supermarket shelves. Much of this increased popularity is attributable to research demonstrating the health benefits of this unique food group, in addition to the fact that rates of chronic disease are significantly lower in populations that frequently consume soy foods (especially the Japanese). But is soy really all it’s made out to be? And how much is too much?

What are soy foods?

Soy-foods include soy milk, soya beans, soy nuts, soy cheese, soy yoghurt, soy infant formulas, tofu, edamame (green soybeans) and tempeh (chunky soybean cake). These foods are good sources of protein and plant-based compounds and biologically active compounds known as isoflavones. Isoflavones are similar in structure to the sex hormone oestrogen and are capable of mimicking the activity of this hormone in the body, which may assist in the prevention and management of chronic disease.

Do soy-foods help to protect against cancer?

Isoflavones have been shown to reduce tumour growth and the spread of cancerous cells in animal studies. Some studies in humans suggest that intake of soy-foods reduces the risk of the development of breast cancer, however this data is limited and therefore no conclusions can be drawn. Importantly, soy-foods are not recommended for individuals with existing breast cancer, as they have been shown to negate the effects of some anti-cancer medications.

Do soy-foods affect menopause symptoms?

Initially it was thought that isoflavones may help to reduce menopausal symptoms that occur due to the reduced levels of oestrogen, such as urinary tract infections, hot flushes and menstrual irregularities, however more recent research indicates that soy foods have little effect on these symptoms.

Do soy-foods affect fertility?

The evidence is not clear in this area. Intake of soy supplements may affect hormone levels in women of child-bearing age, leading to adverse affects on fertility, however this link has not been proven and intake of soy from common foods is unlikely to reduce fertility.

Is it safe to consume soy foods during pregnancy?

When taken in amounts found commonly in foods, soy is likely safe to consume during pregnancy . Soy or isoflavone supplements are not recommended during pregnancy as extremely high intakes may lead to abnormal foetal development.

Do soy-foods reduce the risk of developing heart disease?

Soy -foods are high in fibre, low in saturated or ‘bad’ fat and high in unsaturated or ‘good’ fat. Due to these properties, high intake of soy-foods may result in reduced LDL or ‘bad’ cholesterol in individuals with either high or normal cholesterol levels. As LDL cholesterol is associated with the development of heart disease, this reduction is favourable for heart health.

What affect do soy-foods have on thyroid function?

There is no reliable evidence to suggest that consumption of soy-products affects thyroid function in healthy adults. However, soy products may interfere with the absorption of some medications used to treat underactive thyroid, which could lead to alterations in thyroid function.

How much soy should I have?

In the United States, the Food and Drug Administration states that “25g of soy protein, along with a diet that is low in saturated fat and cholesterol, may help to reduce the risk of heart disease”. Based on this data, two to four servings of soy-foods per day is safe and sufficient to promote health benefits. Higher intakes are unlikely to lead to additional health benefits.

How much is a serve of soy?

    • ½ cup tofu or tempeh
    • 1 cup soymilk
    • 1 cup soy yoghurt
    • 1/2 cup cooked edamame
    • 1 soy pattie burger

Tips to increase soy intake

  • Use soy milk in sauces, gravies, mashed potato, puddings and cakes
  • Choose soy cheese and yoghurt in place of dairy varieties
  • Add tofu to stir fries, soups and pasta dishes
  • Add soy protein powder to smoothies, sauces and soups
  • Try soy meat alternatives such as soy burgers, hot dogs and nuggets

What does this mean for me?

All healthy people would benefit from the addition of soy-foods to their diet because they contain little or no saturated fat, high quality protein and dietary fibre, and may reduce the risk of heart disease and some cancers. Keep in mind that nearly all of the concerns regarding soy-food are based on animal studies which cannot be applied to humans. However, to be on the safe side, it’s probably best to keep soy intake to everyday foods and avoid soy or isoflavone supplements, unless directed otherwise by your doctor.

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