Mediterranean Diet and Breast Cancer Risk

In the past we've reported on the links (or lack thereof) between soy and breast cancer (good for breast cancer survivors [Bite 12/09/09], may help reduce overall risk [Bite 08/27/08]), calcium supplements and breast cancer (makes no difference [Bite 02/11/09]), red meat (may increase risk [Bite 11/15/06]), and grapefruit (does not increase risk [Bite 07/23/08]).

We know that following a Mediterranean style diet is linked with lower incidence of heart disease, high blood pressure, and cancers. Until recently, few studies have looked specifically at the Mediterranean Diet and the risk of breast cancer. Those studies that have been published have looked at only olive oil and breast cancer, or have taken place in the United States, where most people do not adhere to a Mediterranean Diet. What has been lacking has been a study focused on the Mediterranean Diet in a country where the Mediterranean Diet is the dominant style of eating. Fortunately, a study just published in the American Journal of Clinical Nutrition (2010;92(3):620-5) does just that.

Researcher Antonia Trichopoulou and her team made use of data gathered in the Greek portion of a large-scale European study known as EPIC (European Propective Investigation into Cancer and Nutrition). For their study, they focused on nearly 15,000 Greek women who joined the study when they were between the ages of 20 and 86.

At the start of the study, each woman answered a detailed food-frequency questionnaire that addressed their usual style of eating within the previous year. They also responded to questions about their lifestyle, including smoking status and amount of physical activity, and their reproductive history. Further, their Body Mass Index was calculated and recorded, and those with a history of cancer were excluded from the study.

Using the food-frequency questionnaire, the researchers were able to calculate each woman's adherence to the Mediterranean Diet by assigning a score ranging from 0 to 9. For those components of the diet that are frequently eaten, such as vegetables, legumes or fish, the women received a score of 1 if their intake was above average, and a 0 if their consumption was below average. Similarly, for those components that are less frequently eaten, such as dairy or red meat, those women who ate less than the average amount also received a 1, while those who ate more than the average received a 0. (This scoring system is a standard one used often in studies of The Mediterranean Diet.)

After an average follow-up of almost 10 years, the researchers compared the incidence of breast cancer with each woman's Mediterranean Diet score. After controlling for such variables as age, smoking status, physical activity, Body Mass Index and use of hormone replacement therapy, the researchers found that overall, there was no statistically significant link between higher Mediterranean Diet adherence and the risk of breast cancer.

But don't stop reading there - they then grouped the women in pre- and post-menopausal status at the start of the study and compared their Mediterranean Diet scores with their risk of breast cancer. And they found that for postmenopausal women, those who had high scores on the Mediterranean Diet adherence scale - that of a 6 to 9 - were 41% less likely to develop breast cancer than those whose scores were low - 0 to 3. In fact, an increase of just 2 points on the Mediterranean Diet scale decreased a postmenopausal woman's risk of breast cancer by 22%.

What this means for you

Dr. Trichopoulou and her team calculated that among this population, about 10% of all breast cancer cases could have been avoided if all women scored at least a 6 on the Mediterranean Diet scale. And this is among Greeks, who already tend to follow a Mediterranean Diet. It's easy to increase your adherence to the Mediterranean Diet and have a big impact on your risk of breast cancer: just look at the Mediterranean Diet section on this website and pick just two elements for you to get more of. Snack on more nuts, for example, and switch to olive oil instead of butter for frying. Little changes here can make a big impact.

First posted: September 15, 2010