Study shows that diet heavy on olive oil cuts breast cancer risk by 62%.


Breast cancer, the most frequently diagnosed malignant tumor and the leading cause of cancer death among women, has increasing incidence rates. In 2012, 1.7 million women received a diagnosis of breast cancer. Since the 2008 estimates, breast cancer incidence has increased by more than 20% worldwide, while mortality has increased by 14%.

Diet has been extensively studied as a modifiable component of lifestyle that could influence breast cancer development. Epidemiological evidence on the effect of specific dietary factors is still inconsistent, and the only convincing evidence relates to an increased risk in women with high alcohol consumption.   Now, a study from researchers at the University of Navarra has shown that a Mediterranean diet reduces the risk of developing breast cancer by two thirds.  The team state that it is the first scientific study that demonstrates the preventive value of the Mediterranean diet against breast cancer with randomized trials.  The opensource study is published in the Journal American Medical Association (JAMA).

Previous studies have targetted the Mediterranean dietary pattern because, historically, breast cancer rates have been lower in Mediterranean countries than in Northern or Central European countries or the United States.  The Mediterranean diet is characterized by an abundance of plant foods, fish, and especially olive oil. In the Lyon Diet Heart Study, participants allocated to a cardioprotective Mediterranean-type diet showed a 61% lower risk of cancer (all subtypes) than those participants allocated to a control diet close to the step 1 American Heart Association prudent diet.  The lab note that earlier studies to evaluate the association between a Mediterranean diet and breast cancer risk were not randomised.  The group state that to their knowledge their’s is the first scientific study that demonstrates the preventive value of the Mediterranean diet against breast cancer with randomised trials. 

The current study observed 4,282 women over an average of 4.8 years.  The participants followed three types of diets, a Mediterranean diet rich in extra virgin olive oil, a Mediterranean diet with the addition of nuts, and a diet low in fat to function as a control group.   The women were an average age of 67.7 years old, had an average body mass index of 30.4, most of them had undergone menopause before the age of 55 and less than 3 percent used hormone therapy. During a median follow-up of nearly five years, the lab identified 35 confirmed incident (new) cases of malignant breast cancer.

Results showed that in the first two groups, the results from the participants confirm that they had one third of the incidence of the disease as compared to the control group.  Data findings show that the high consumption of virgin olive oil in the Mediterranean diet explains in large part the protection against breast cancer. The researchers note that even though the control group also followed a diet that is considered healthy, the results could have been even more significant if they had compared those following a normal diet in western, not Mediterranean countries.

Data findings show that women eating a Mediterranean diet supplemented with extra virgin olive oil showed a 62% relatively lower risk of malignant breast cancer than those allocated to the control diet. In contrast, women eating a Mediterranean diet supplemented with nuts showed a nonsignificant risk reduction compared with women in the control group.

The team note a number of limitations in their study including that breast cancer was not the primary end point of the trial for which the women were recruited; the number of observed breast cancer cases was low; the lab do not have information on an individual basis on whether and when women in the trial underwent mammography; and the study cannot establish whether the observed beneficial effect was attributable mainly to the extra virgin olive oil or to its consumption within the context of the Mediterranean diet.

The researchers surmise that their study shows that dietic intervention could have especially valuable results because it can be used in primary care centers and, in the case of the Mediterranean diet, can contribute to other benefits that have already been shown such as the prevention of diabetes type 2, cardiovascular disease and obesity. For the future the lab will conduct further randomized clinical studies to validate their findings.

Source: University of Navarra

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