There is a robust amount of published research, including major clinical trials, on the ability of the Mediterranean diet (MeDiet) to protect against cardiovascular disease —now, according to results from the PREDIMED trial, it might also prevent breast cancer. One can easily read the specifics of the MeDiet on the internet and some excellent books, but this diet is basically an abundance of plant foods, fish, and olive oil. The PREDIMED study —was stopped early in 2009, due to the cardiovascular benefits of the MeDiet compared with a low-fat diet. A secondary outcome on breast cancer incidence how now been released. The results suggest that a benefit of the MeDiet supplemented with extra-virgin olive oil provides primary prevention of breast cancer. This is the first randomized trial to see the effect of a long-term dietary regimen on breast cancer incidence. In 4282 postmenopausal women, and with a follow-up of 4.8 years, the observed rates for breast cancer were 1.1 for those on the MeDiet supplemented with extra virgin olive oil (1 liter per week for the woman and her family), 1.8 for MeDiet with supplemented nuts (mixed nuts=walnuts 15 g, hazelnuts 7.5 g, and almonds 7.5 g), and 2.9 for those women on a low-fat diet. The risk for a malignant breast cancer was significantly 62% lower in women randomized to the MeDiet supplemented with extra-virgin olive oil compared to those randomized to the low-fat diet. The MeDiet supplemented with nuts was also associated with a lower risk, but it was not statistically significant, as was the diet with the extra virgin olive oil. While the number of breast cancer cases was small (35 confirmed cases out of those 4282 women, the results are statistically significant.
While the study has multiple limitations such as the women were not all screened for breast cancer with mammography, they were all Caucasian and postmenopausal, and they had to be at high risk for cardiovascular disease in order to be enrolled in the trial.
All types of olive oil contain a high supply of monounsaturated fatty acids, mainly oleic acid, as well as squalene, but extra virgin is a thinner, more viscous oil, and contains active compounds such as several polyphenols. It is thought that the olive oil is antiproliferative against cancer cells by affecting the expression of human oncogenes, and the MeDiet with its high amount of plant foods and fish oils, is anti-inflammatory and reduces DNA oxidative damage.
Reference: Toledo E, Salas-Salvado 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
JAMA Intern Med. Published online September 14, 2015. doi:10.1001/jamainternmed.2015.4838