You’re correct in believing that extra virgin olive oil is an essential part of the Mediterranean diet, which focuses on a composite of the traditional cuisines of Spain, southern France, Italy, Greece, Crete and parts of the Middle East. The diet emphasizes fish, nuts, legumes, fruits, vegetables and olive oil. The new finding that providing the women with a set amount of extra virgin olive oil to consume daily can reduce the risk of breast cancer comes from researchers in Spain who tested two versions of the Mediterranean diet and compared them to a low-fat diet. All told, 4,282 women whose average age was 68 participated. One group was asked to follow the Mediterranean diet, and each woman in the group was given one liter of extra virgin olive oil per week and instructed to consume four tablespoons per day. The second group followed the Mediterranean diet, but instead of the olive oil they consumed an ounce of mixed nuts a day, consisting of 15 grams of walnuts (about half an ounce) as well as 7.5 grams (about one-quarter ounce) of hazelnuts and 7.5 grams of almonds. The third group of women served as controls and was simply advised to reduce intake of fat.
Over the next 4.8 years, 35 of the women developed breast cancer. The researchers reported that those who were following the Mediterranean diet with extra virgin olive oil had a risk that was 68 percent lower than the women in the control group. There was no statistically significant reduction in breast cancer risk among the women whose diets were supplemented with nuts.
We know from earlier studies that the Mediterranean diet protects against heart disease, stroke and death from heart disease by as much as 30 percent, even among high-risk individuals. This latest study linking the Mediterranean diet with extra virgin olive oil to reduced breast cancer risk was very similar to a study published in 2013 that showed the 30 percent reduction in heart disease risk. In that study, there was also a control group following a low-fat diet, a group given extra virgin olive oil and told to consume four tablespoons per day and a group that ate the same amount of mixed nuts as the women in the breast cancer study.
We’ll need longer-term studies to confirm that adding an extra helping of extra virgin olive oil to the Mediterranean diet really does lower the risk of breast cancer, as well as research to determine what it is about extra virgin olive oil that might be responsible for the benefit.
Andrew Weil, M.D.
Miguel A. Martinez Gonzales et al, “Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial.” JAMA Internal Medicine, September 14, 2015, doi:10.1001/jamainternmed.2015.4838