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Researchers reveal soya’s effects on breast tissue

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by Cancer Research UK | News

5 July 2002

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Eating a diet rich in soya products such as tofu can affect the make-up of breast tissue, potentially reducing the risk of breast cancer, according to a new study1 from Cancer Research UK.

Scientists have previously suggested that soya intake might contribute to the low rates of breast cancer in countries like China and Japan but research has proved inconclusive.

However, the new findings from a collaborative study involving scientists from the National University of Singapore, Cancer Research UK and the US National Cancer Institute add weight to the theory and point to a possible mechanism for this protective effect.

The researchers combined data from two studies of women living in Singapore in order to analyse in detail the effects of diet on women’s breast tissue.

The first study focused on women’s eating habits, including their intake of soya, while the second used mammograms to classify women according to the density of their breast tissue. Previous research has shown that dense tissue, which can be observed with a breast X-ray, is associated with an increased risk of breast cancer.

By identifying a group of 406 women who took part in both these studies the researchers were able to see how diet affected breast tissue and tell who was most likely to develop breast cancer.

They found that women who ate the most soya were 60 per cent less likely to have ‘high risk’ breast tissue than women with the least soya in their diet.

The study’s co-author, Dr Stephen Duffy of the charity’s Mathematics, Statistics and Epidemiology Department in London says: “There has always been a question mark over a connection between soya and breast cancer – some studies have suggested a link but others haven’t.

“This research shows for the first time how the amount of soya a woman eats may have a affect on breast tissue and in turn may potentially reduce her risk of breast cancer.”

Scientists think that the active ingredient in soya is isoflavone – a chemical that mimics the action of the female sex hormone oestrogen. However, these ‘plant oestrogens’ are not as strong as the oestrogen produced by the body.

Exposure to these plant oestrogens seem to lengthen a woman’s menstrual cycle. Previous research has suggested that the fewer menstrual cycles a woman goes through in her lifetime, the lower her risk of breast cancer.

Sir Paul Nurse, Interim Chief Executive for Cancer Research UK says: “Breast Cancer now affects nearly 40,000 women in the UK every year making it the most common form of cancer. That’s why it’s vital that we find new ways of preventing the disease.

“These findings make an important contribution towards our on going studies on the relationship between diet and cancer and may eventually point to new ways of preventing breast cancer.”



  1. Cancer Epidemiology, Biomarkers and Prevention11 (7)