Diet With Extra Olive Oil May Lower Risk of Breast Cancer

Olive Oil

A study to test the effects of the Mediterranean diet on the prevention of cardiovascular disease yielded an unexpected result—the Mediterranean diet supplemented with extra virgin olive oil (EVOO) lowered the risk of breast cancer in older women by 68%.

The study, published online by JAMA Internal Medicine, was a secondary analysis of the PREDIMED trial, which involved 4282 women in Spain aged 60 to 80 and at high risk of cardiovascular disease.

From 2003 to 2009, the women were randomly assigned to eat the Mediterranean diet supplemented with EVOO (n = 1476), the Mediterranean diet supplemented with 30 g per day of mixed nuts, including walnuts, hazelnuts, and almonds (n = 1285), or the control diet with advice to reduce daily fat intake (n = 1391). Participants in the Mediterranean group with EVOO were given 1 liter per week.

The women were an average age of 67.7, had an average BMI of 30.4, most were postmenopausal, and less than 3% used hormone therapy.

After a median follow-up of nearly 5 years, researchers identified 35 confirmed new cases of malignant breast cancer. They found that the women eating the Mediterranean diet supplemented with EVOO had a 68% (multivariable-adjusted hazard ratio [HR], 0.32) relatively lower risk of malignant breast cancer than those on the control diet (95% CI, 0.13-0.79).

“The results of the PREDIMED trial suggest a beneficial effect of a MeDiet (Mediterranean diet) supplemented with extra virgin olive oil in the primary prevention of breast cancer,” the authors concluded. “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 centers and also offers beneficial effects on a wide variety of health outcomes.”

Women eating the Mediterranean diet with nuts did not show significant risk reduction compared to those on the control diet (HR, 0.62 [95% CI, 0.29-1.36]).

The authors noted several limitations with the study, including that breast cancer was not the primary endpoint of the original trial which the women were recruited for and that the study did not establish if the reduced risk of breast cancer was attributable to EVVO or its consumption along with the Mediterranean diet.

“Of course, no study is perfect. This one has a small number of outcomes (only 35 incident cases of breast cancer), the women were not all screened for breast cancer with mammography, they were not blinded to the type of diet they were receiving, and all were white, postmenopausal and at high risk for cardiovascular disease,” JAMA Internal Medicine deputy editor Mitchell H. Katz, MD, wrote in an editor’s note on the study findings.

“Still, consumption of a Mediterranean diet, which is based on plant foods, fish, and extra virgin olive oil, is known to reduce the risk of cardiovascular disease and is safe. It may also prevent breast cancer. We hope to see more emphasis on Mediterranean diet to reduce cancer and cardiovascular disease and improve health and well-being.”

The results of this secondary analysis need to be confirmed in longer-term, larger studies, the authors noted.

Toledo E, Salas-Salvadó J, Donat-Vargas C, et al. Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial: A Randomized Clinical Trial [published September 14, 2015]. JAMA Intern Med.