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Soya: the health protector - The health effects of SoyaBreast CancerThere is some controversy about the possible role of soya in breast cancer. It has been suggested that the limited oestrogen-like effect of isoflavones may be detrimental for postmenopausal women whose oestrogen levels have dropped and have been diagnosed with hormone-sensitive (oestrogen-receptor or ER positive) breast cancer.
These types of study have produced mixed results and their relevance to human breast cancer patients is unclear. To date there have been only two human studies and these were also unclear (Petrakis et al., 1996; Hargreaves et al., 1999). There is, however, strong evidence that eating soya foods during adolescence reduces the risk of breast cancer later in life. One of the first studies to report this was the Shanghai Breast Cancer Study, the largest population-based study looking at lifestyle and breast cancer (Shu et al., 2001). It looked at 1,400 breast cancer cases in China and found that women If consuming phytoestrogens was dangerous for postmenopausal women with breast cancer, then you’d expect the medical profession to advise that they stop consuming all oestrogen too as it is far more potent (Coldham et al., 1997). This would mean recommending they avoid all cow’s milk and dairy products which account for 60-80 per cent of the oestrogen in the Western die (Hartman et al., 1998). The rest coming mainly from meat and eggs. Cow’s milk actually contains a cocktail of over 35 different hormones and 11 growth factors (Grosvenor et al., 1992). Furthermore, modern dairy cows (including organically farmed cows) are frequently impregnated while still producing milk (Webster, 2005). At least two-thirds of retail milk in the UK is taken from pregnant cows when the hormone level in the milk is markedly elevated (Danby, 2005). Some scientists are far more concerned about the effects of these hormones on human health. This is a much neglected area of research and there is a need to update the information we have about hormones in cow’s milk and dairy products (Jouan et al., 2006). For more information, see the VVF’s guide on breast cancer, A Fighting Chance who consumed the most soya as teenagers had half the risk of breast cancer as adults. A year later, over 1,000 Asian-American women, including 501 breast cancer patients, were asked how often they ate soya foods such as tofu, soya milk and miso. Results showed that those who consumed soya at least once a week during adolescence had a significantly reduced risk of breast cancer (Wu et al., 2002). More recently, a study of more than 1,500 Asian American women found that eating soya foods during childhood could reduce the risk of breast cancer by 60 per cent (Korde et al., 2009). The greatest protective effect was seen in those eating soya six times a month, compared to less than three, from childhood onwards. A further protective effect was also seen in those who ate soya during adolescence and adulthood. The protective effect of soya was recently shown to apply to women who have breast cancer too. The Shanghai Breast Cancer Survival Study looked at over 5,000 women (aged 20 to 75) previously diagnosed with breast cancer an average of four years earlier (Shu et al., 2009). Results showed that those who ate more soya foods (11 grams of soya protein per day, equivalent to one and a half servings of tofu or soya milk) were less likely to die from the disease and had a significantly lower risk of recurrence. The protective effectof soya applied to both premenopausal and postmenopausal women. The conclusion was that the prognosis for women with breast cancer was improved by eating soya foods. Taken together, these studies indicate that eating soya foods during adolescence reduces the risk of breast cancer and that the risk continues to fall if women carry on eating soya as adults. Furthermore, contrary to some unfounded reports, soya foods appear to protect against breast cancer in both premenopausal and postmenopausal women with the disease. This research should reassure women diagnosed with breast cancer that soya foods are safe and potentially beneficial. For those who are still concerned, a cautious approach would be for postmenopausal women at risk of breast cancer to limit the number of soya products they eat to three or four a week.
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The theory is that the weak oestrogen-like activity of soya isoflavones may stimulate the growth of those tumours which are sensitive to oestrogen. This is not a concern for premenopausal women who have much higher levels of circulating oestrogen. Again, these concerns are based largely on the results of in vitro (test tube) and animal experiments.
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