An Olive Oil May Enhance Mediterranean Diet Gains in Older Women

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A new study suggests that incorporating additional extra virgin olive oil into the Mediterranean diet seems to reduce the risk of breast cancer in postmenopausal women.

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The Mediterranean diet has been espoused as the healthiest diet for avoiding all sorts of ailments, from heart disease to various types of cancer. This diet plan involves consumption of foods commonly eaten by populations around the Mediterranean Sea, which includes mostly fish, oils from nuts, olive oil, and fruits, beans, nuts and legumes. Red meat and sweets are eaten only rarely. A new study, just published in JAMA Internal Medicine, suggests that this diet might help prevent breast cancer in postmenopausal women especially when additional extra virgin olive oil (EVOO) is added.

A group of researchers, led by Dr. EstefanÃa Toledo from the University of Navarra School of Medicine, Navarra, Spain randomly assigned about 4,300 postmenopausal women (approximately 67 years of age) to one of three dietary groups: Group 1 -- consumed the Mediterranean diet supplemented by extra EVOO; Group 2 -- ate the Mediterranean diet supplemented by extra mixed nuts; Group 3 -- ate a control diet in which they were advised to restrict dietary fat.

All three groups were all given periodic education and were evaluated with respect to adherence to their assigned diets, and those receiving supplemental EVOO or nuts were provided with those items for free during the study. The women were all at increased risk of cardiovascular disease, and as such were enrolled in a study (the PREDIMED study) to examine the effect of these diets on the incidence of heart disease. Thus, the effect of the diets on breast cancer was a subsidiary, or secondary study. They were followed for a median period of about five years, and were evaluated for the occurrence of new cases of invasive breast cancer.

The researchers found that compared to Group 3 -- the control group -- those receiving the additional EVOO had a 68 percent lower risk of developing invasive breast cancer, a difference that was statistically significant, while the risk of the group eating additional nuts had a 41 percent lower risk (which was not statistically significant).

They concluded that the "results suggest a beneficial effect of a Mediterranean diet supplemented with extra-virgin olive oil in the primary prevention of breast cancer. These results come from a secondary analysis of a previous trial and are based on few incident cases and, therefore, need to be confirmed in longer-term and larger studies."

ACSH senior nutrition fellow Dr. Ruth Kava added that "these data certainly seem to support the value of the Mediterranean diet and olive oil in breast cancer avoidance, but as the authors stated, this study alone is not sufficient to change public policy." She added that "these results were obtained in older women, and it isn't clear to what extent they might also hold true for younger women. More studies are definitely needed to clarify these results."