Soya could lower breast cancer risk, say researchers

Women who eat a diet that is rich in soya products such as tofu may reduce their risk of breast cancer, research suggests today.

Women who eat a diet that is rich in soya products such as tofu may reduce their risk of breast cancer, research suggests today.

The plant proteins, dietary staples throughout Asia, appear to affect the make-up of breast tissue, according to scientists from Cancer Research UK.

They found that women who ate a lot of soya were much less likely to develop "dense" tissue associated with breast cancer. Low rates of breast cancer in countries such as China and Japan have for many years been thought to be related to the high intake of soybean foods.

But research had proved inconclusive until the latest work, by experts from the National University of Singapore, the US National Cancer Institute, and Cancer Research UK.

They used data from two studies of women living in Singapore, combined to analyse the effect of diet on their breast tissue.

One focused on women's eating habits, including their intake of soya. The other used mammograms to class women according to the density of their breast tissue.

The researchers identified a group of 406 women who took part in both studies. They found that women who ate the most soya were 60 per cent less likely to have "high risk" breast tissue than those who ate the least.

Dr Stephen Duffy, from 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 may potentially reduce her risk of breast cancer."

Scientists think the active ingredient in soya is isoflavone – a member of a family of plant chemicals called phytoestrogens that mimic that action of the female sex hormone oestrogen.

Many cases of breast cancer are largely caused by the way oestrogen acts on breast tissue. Isoflavone may block oestrogen in the breast, and its own action is weaker than that of the natural hormone. Exposure to phytoestrogens seem to lengthen a woman's menstrual cycle. Previous research suggested the fewer menstrual cycles a woman went through in her life, the lower the risk of breast cancer.

Sir Paul Nurse, interim chief executive of Cancer Research UK, said: "These findings make an important contribution towards our ongoing studies between diet and cancer, and may eventually point to new ways of preventing breast cancer."