For years, scientists have thought that olive oil might help prevent breast cancer.
Now they may have discovered why.

In laboratory experiments, oleic acid, the main monounsaturated fatty acid in olive oil, suppressed one of the most important genes involved in breast cancer.

"This is the first molecular support for the Mediterranean diet," said study author Javier Menendez, a research scientist with the Evanston Northwestern Healthcare Research Institute in Illinois. The report appears in the Jan. 10 issue of the Annals of Oncology.

Others, however, urged caution in interpreting the findings.

"It's an interesting story, but it's all done in cell cultures and that's not necessarily how it will interact in the body," said Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in New Orleans.

"It certainly is very promising, but there is a very long way to go between doing this in an animal or human context versus doing it on cells in a test tube," added Dr. Marleen Meyers, a medical oncologist with the New York University Cancer Institute.

Epidemiological studies have reported lower rates of breast cancer in people from the Mediterranean region, where a lot of olive oil is produced and consumed. This has led to speculation that the diet, including olive oil, may be responsible.

No one knows, however, if the protective effect can be found in olive oil, or in another ingredient besides oleic acid in olive oil, or in another food or if it has nothing whatsoever to do with diet and instead can be attributed to genetics.

For this study, Menendez and his colleagues examined human breast cancer cells that had been grown for this research.