Unfortunately, most of us know someone who has suffered from or is still suffering from breast cancer. Breast cancer, after lung cancer, is the second most commonly diagnosed malignancy in women in most countries around the world. In 2007, about 1.3 million occurrences of breast cancer were diagnosed worldwide and 400,000 cases led to the death of a patient. In fact, breast cancer patients account for about 34% of all women living worldwide with cancer, and this number continues to steadily rise. In the United States alone, about 1 in 8 women (~12%) will develop invasive breast cancer over the course of her lifetime. This phenomenon is believed to result from reduced physical activity1, reproductive changes2, and the widespread use of hormone replacement therapy3.
The Mediterranean diet, which is the traditional dietary pattern of people living in Mediterranean countries, is considered one of the healthiest, nutrient-rich diets. This diet, comprised primarily of fresh fruits and vegetables, fish, legumes whole grains, herbs and extra virgin olive oil, contains high levels of antioxidants and shows anti-inflammatory properties that are crucial in the prevention of breast cancer. Focus has recently been placed on extra virgin olive oil, the predominant fat in the Mediterranean diet, in the prevention of the disease. The natural antioxidants in extra virgin olive oil, including phenols, sterols, carotenoids, tocopherol, and squalene, can protect the body from adverse effects caused by free radicals, unstable biological molecules that can be toxic to the body4. Vitamin E, naturally abundant in extra virgin olive oil, can further protect the body against the accumulation of free radicals and lipid peroxidases – products of the chemical damage done by free radicals on cellular membranes. Lower concentrations of vitamin E can promote an increase in the incidence of some cancers, because of a lowered antioxidant potential5. Moreover, alpha-tocopherol, a form of vitamin E, can inhibit premalignant stages of breast cancer in women6.
The most significant study to date on the effect of extra virgin olive oil on breast cancer was observed in a cohort of women in Spain from 2003 to 2009. The study involved 4282 women aged 60 to 80 years who were at a high risk of cardiovascular disease6. They were randomly assigned to three groups: 1) the Mediterranean diet with the addition of extra virgin olive oil, 2) Mediterranean diet supplemented with a variety of nuts or 3) control diet with a reduced fat content. After a follow-up of 4.8 years, 35 confirmed cases of breast cancer were identified. There were 63% more cases reported in group 2 (nuts) compared to the diet with increased amount of extra virgin olive oil; and 163% more cases in the control group compared to the olive oil group. This was the first randomized controlled trial showing the effect of long-term dietary modification on the incidence of breast cancer. The results suggest a beneficial effect of Mediterranean diet with the addition of extra virgin olive oil in primary prevention of breast cancer.
In a more recent clinical trial performed at Piacenza Hospital in Italy, women who were in remission from breast cancer were tracked for a period of three years7. One group of 199 women were asked to eat a Mediterranean diet rich in extra virgin olive oil, while another group of 108 women were asked to eat their normal diet, with input from a dietician. The results showed that during that time, 11 patients suffered cancer again who were following their normal diet, while no women in the Mediterranean diet group experienced a relapse7. Although the study had a limited sample size and short follow-up time, the results are telling and highlight the need for further research. More work must be done to determine the long-term effects of the Mediterranean diet on breast cancer in women of various ethnic backgrounds, as well as on the specific mechanism(s) by which extra virgin olive oil and other dietary components may exert their protective effects on the disease.