Monday Sept 14, 2015 (foodconsumer.org) -- Mediterranean diet supplemented with extra virgin olive oil may be protective against breast cancer, according to a new study published in JAMA Internal Medicine.  Extra virgin olive oil is full of naturally occurring antioxidative phenols, which may render this protective effect.

The study shows women aged on average at 67.7 years who followed a Mediterranean diet supplemented with extra virgin olive oil for five years were 68% less likely to be diagnosed with breast cancer, compared with those who ate an ordinary Mediterranean diet.   

Keep in mind that those women had an average body mass index of 30 kg/m2 and were considered at high risk for cardiovascular disease.  The study was designed to test the potential effect of dietary patterns on the risk of cardiovascular disease.  It is unknown how this diet would affect the breast cancer risk in women who had a normal body weight and were not at high risk for cardiovascular disease.

For the study, Dr. Miguel A. Martínez-González of the University of Navarra in Pamplona and CIBEROBN in Madrid, Spain and colleagues let 4,282 women use either an ordinary Mediterranean diet or a Mediterranean diet supplemented with one liter of extra virgin olive oil per week or a Mediterranean diet supplemented with 30 grams of nuts (15 grams of walnuts, 7.5 grams of almond and 7.5 grams of hazelnuts) per day.

The researchers found the Mediterranean diet supplemented with olive oil during a five-year intervention associated with a 68% lower risk for breast cancer while the Mediterranean diet supplemented with nuts was not associated with significantly reduced risk compared with the ordinary Mediterranean diet.

The study has its limitations.  The study was not designed to examine how the Mediterranean diet affects the risk of breast cancer.  And the number of observed breast cancer cases was only 35, which was small. 

Scientists believe that Mediterranean diet, which is full of plant-based foods such as vegetables and olive oil and beans, protects against breast cancer because it has a high total antioxidative capacity.   Antioxidants lower oxidative stress, which promotes the development of breast cancer.

The protective effect of the Mediterranean diet varies from person to person.  A new study published in European Journal of Nutrition shows that the diet was more protective against breast cancer in those Greek-Cyriot women who carried wild-type MnSOD or CAT SNPs.  (David Liu)

Maria G. Kakkoura, Christiana A. Demetriou, Maria A. Loizidou, Giorgos Loucaides, Ioanna Neophytou, Simon Malas, Kyriacos Kyriacou , Andreas Hadjisavvas, MnSOD and CAT polymorphisms modulate the effect of the Mediterranean diet on breast cancer risk among Greek-Cypriot women, 

European Journal of Nutrition, First online: 01 July 2015