Scientists have discovered why eating a Mediterranean diet rich in fruits, vegetables and particularly olive oil can help to protect women from developing breast cancer.
The key is oleic acid, the main component of olive oil.
Dr Javier Menendez, of Northwestern University in Chicago in the United States, said oleic acid blocks the action of a cancer causing oncogene called HER-2/neu.
HER-2/neu is found in about 30 per cent of breast cancer patients.
"We have something now that is able to explain why the Mediterranean diet is so healthy," Dr Menendez said.
Doctors and researchers had been aware that eating a Mediterranean diet reduced the risk of breast cancer and other illnesses, such as heart disease.
But until now they did not know how.
Dr Menendez and his colleagues in the United States and Spain studied the impact of oleic acid in laboratory studies of breast cancer cells.
"We are able to demonstrate that the main component of olive oil, oleic acid, is able to down regulate the most important oncogene in breast cancer," Dr Menendez said.
"The most important source of oleic acid is olive oil."
They found that oleic acid not only suppressed the action of the oncogene, it also improved the effectiveness of the breast cancer drug Herceptin.
Herceptin is a targeted therapy made by Swiss drug maker Roche that works against the HER-2/neu gene.
"There is no evidence at all that olive oil is toxic," Dr Menendez said.
"It is totally safe to consume olive oil."
Dr Menendez stressed that although the laboratory results are promising, more research is needed.
His findings were published in the journal Annals of Oncology.
More than one million cases of breast cancer are diagnosed worldwide each year.
