A Mediterranean diet boosted by additional olive oil may protect against breast cancer, research has shown.
Scientists compared the effect of an olive oil-rich "healthy" Mediterranean diet with simple advice to cut down on fat in a group of 4,282 Spanish women.
Over a period of about five years, participants on the Mediterranean diet supplemented with extra virgin olive oil (Evoo) were 68% less likely to develop breast cancer than those given health advice.
The classic Mediterranean diet is characterised by an abundance of plant foods, fish and olive oil.
Two varieties of the diet were studied, one supplemented by a weekly litre of extra virgin olive oil and the other by 30g a day of mixed nuts.
The nut-supplemented diet had a non-significant effect on breast cancer risk, highlighting the importance of olive oil.
Dr Miguel Martinez-Gonzalez, from the University of Navarra in Pamplona, Spain, led the Predimed trial researchers whose findings appear online in the journal Jama Internal Medicine.
They wrote: "The results of the Predimed trial suggest a beneficial effect of a MeDiet (Mediterranean diet) supplemented with Evoo in the primary prevention of breast cancer.
"Preventive strategies represent the most sensible approach against cancer. The intervention paradigm implemented in the Predimed trial provides a useful scenario for breast cancer prevention because it is conducted in primary health care centres and also offers beneficial effects on a wide variety of health outcomes. Nevertheless, these results need confirmation by long-term studies with a higher number of incident cases."
Dr Mitchell Katz, deputy editor of Jama Internal Medicine, pointed out that only 35 cases of breast cancer were seen during the study and the women were not blinded to the type of diet they were receiving.
But he added that the Mediterranean diet was known to reduce the risk of heart disease and was safe.
"It may also prevent breast cancer," said Dr Katz. "We hope to see more emphasis on Mediterranean diet to reduce cancer and cardiovascular disease and improve health and well-being."
Katie Goates, senior research communications officer at the charity Breast Cancer Now, said: "Although these results raise an interesting question about the role of the Mediterranean diet and olive oil in reducing breast cancer risk, they don't add anything more concrete to our understanding of diet and breast cancer.
"We already know that maintaining a healthy diet might help to reduce your risk of breast cancer, but without more evidence about the role of specific foods on breast cancer risk, clearer guidelines are some way off."