What is soya?
Soy beans and foods made from soy beans are excellent sources of protein for people who follow a vegetarian diet. Soya (soymilk, soya nuts, soy beans, tofu and edamame [green soybeans]) is one of the few plant foods that contain a range of essential nutrients including high quality protein, fibre, unsaturated fats and a variety of vitamins and minerals.
Health benefits of soy
Soy foods contain isoflavones which are plant oestrogens. These are also known as phytoestrogens, a subclass of plant flavonoids. They have a similar but not identical chemical structure compared to the human hormone oestrogen.
Evidence based research have found that in combination with a healthy diet, isoflavones have beneficial effects including reducing the risk for diseases of lifestyle such as cardiovascular disease, cancer, osteoporosis, and for the treatment of menopausal symptoms.
Read: Soy isoflavones could improve mood
The proposed mechanisms is that isoflavones possess antioxidant, anti-inflammatory and anti-coagulative effects. These properties have been associated with the maintenance of blood vessel flexibility and the inhibition of rapid cell overgrowth, which generally occurs in cancer development.
Is it safe to consume soya beans and soya foods?
Soy and hormones
The notion that soy’s phytoestrogen intake may be harmful, especially to men and their maleness is often mentioned in the popular media. Studies however have shown that consuming soya foods, does not raise oestrogen levels, nor does it upset hormonal balance or reduce testosterone levels in men, and no studies have reported adverse effects on fertility or sexual health in men.
Read: Testosterone deficiency
Soy and breast cancer
In 2012, the American Institute for Cancer Research (AICR) reported that there was no indication that consuming soya and soya products placed anyone at increased risk of breast cancer. This applied to those at risk of breast cancer, to breast cancer patients and survivors of breast cancer. The AICR's latest review also mentions that in some cases soya isoflavones may in fact lower the risk of cancer.
Read: Soy may treat colon cancer
A few studies suggest that a constant intake of soya consumption and exposure to isoflavones, especially before and during puberty, may protect against the development of breast cancer. Other studies suggest that soya isoflavones may also lower the risk of recurrence in breast cancer survivors.
Soya and mineral absorption
Soya has been blamed for causing poor mineral absorption. Some plant chemicals found in soya beans such as oxalate and phytates have the potential to weaken the absorption of minerals such as iron, zinc and calcium. However, it depends on the amount and frequency of consumption and recent studies show these minerals are usually well absorbed from soya foods when eaten as part of a healthy diet that includes a variety of foods.
Soy and thyroid function
There are concerns about soy’s negative impact on thyroid health. Some soya foods contain goitrogens, substances that interfere with the production or utilisation of the thyroid hormone thyroxine. Foods that contain goitrogens include cassava, millet, and cruciferous vegetables.
Most of these goitrogens, however, are of no major clinical importance. Studies have confirmed that there is no harmful effect of soya food consumption in healthy humans with a normally functioning thyroid gland. However it is a concern for people with an underactive thyroid gland (hypothyroidism) as soya food consumption may require an increased intake of thyroid medication.
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This is because soya isoflavones can interfere with the absorption of synthetic thyroid hormones. A recent study has indicated that soya isoflavones may worsen the condition in individuals with a mildly underactive thyroid.
Our understanding of the effects of soy isoflavones on the human body and consequent health is evolving with ongoing research. The majority of current studies indicate that the typical amount of soy consumed in the western diet is safe, and even beneficial, for most people. Excessive consumption of soy, or soy supplementation, however, is not recommended.
It is recommended that we enjoy soya and soya products as an alternative to protein from animal origin combined with a diet high in fresh fruit and vegetables, plant oils and whole grains. As with most things in life, there are positive and negative aspects to foods, and the key to a healthy diet is balance, variety and moderation.
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Soy myths & facts. United Soybean Board website. http://www.soyconnection.com/sites/default/files/pictures/soy-myths-facts.pdf. Accessed January 22, 2014
The dietitians from Nutritional Solutions are Health24's expert team of registered dietitians.