A study has found women who eat soya-rich diets have less "high risk" dense breast tissue.

It had been suspected that the high consumption of foods such as tofu and soya beans or milk in countries such as China and Japan contributed to the countries' low breast cancer rates.

But there had been no conclusive scientific evidence to back up the theory.

The amount of soya a woman eats may have an effect on breast tissue and in turn may potentially reduce her risk of breast cancer

Dr Stephen Duffy, Cancer Research UK

Researchers from Cancer Research UK, the National University of Singapore and the US National Cancer Institute looked at the results from two studies carried out in Singapore.

The first looked at the women's diet, the second used mammograms to asses the density of their breast tissue.

It has previously been shown that dense tissue is associated with an increased risk of breast cancer.

Tissue

Four hundred and six women took part in both studies.

The women who ate the most soya were 60% less likely to have the "high risk" breast tissue than women who had the least soya in their diet.

The benefit could from a chemical in soya called isoflavone which mimics the action of the female sex hormone oestrogen, though such "plant oestrogens" are not as strong as the oestrogen produced by the body.

Being exposed to the plant oestrogens appears to lengthen a woman's menstrual cycle.

Previous studies have indicated that the fewer menstrual cycles a woman has in her life, the lower her risk of breast cancer.

Dr Stephen Duffy of the Cancer Research UK's Mathematics, Statistics and Epidemiology Department in London said: "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 an effect on breast tissue and in turn may potentially reduce her risk of breast cancer."

Prevention

Sir Paul Nurse, Interim Chief Executive of Cancer Research UK said: "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.

He added: "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."