Eating a Mediterranean-style diet that emphasizes fish, vegetables and particularly olive oil, may lower women’s risk of breast cancer compared to following a low-fat diet, suggests a new study from Spain.
The Mediterranean diet is known for its abundance of plant foods, fish and especially olive oil. Read 8 tips to follow a Mediterranean-style diet.
In the five-year trial that randomly assigned women to different kinds of diets, those instructed to eat a Mediterranean-style diet with four tablespoons of extra virgin olive oil per day had about half as many breast cancer diagnoses as those on a low-fat diet.
The findings are based on a randomized trial, the gold standard of research.
Still, the authors caution in their report, the data come from a larger long-term trial whose primary focus is heart disease. And out of more than 4,000 women included in the breast cancer study, there were only 35 cases of breast cancer, a low number of total cases for statistical analysis. This and a lack of data about cancer-screening mammograms among the women limit the results.
Researchers from the University of Navarra in Pamplona and CIBEROBN in Madrid, Spain studied breast cancer outcomes in women participating in PREDIMED, a study of the Mediterranean diet’s protective effects against cardiovascular disease and a variety of other illnesses.
Between 2003 and 2009, a total of 4,282 women ages 60 to 80 years old with a high risk of cardiovascular disease were randomly assigned to a Mediterranean diet supplemented with extra virgin olive oil (EVOO), the same diet supplemented with nuts or to a comparison group that was told to reduce their overall dietary fat intake.
Those in the two Mediterranean diet groups were given either one liter (34 ounces) of olive oil per week or 30 grams (1 ounce) of nuts per day. The olive oil group was instructed to consume about 50 grams (4.2 tablespoons) per day, including in cooked foods and on salads or bread.
The women had quarterly sessions with dieticians, completing questionnaires that gauged how well they were following their assigned diet. There was no specific advice to reduce overall calorie intake or to increase physical activity.
Over the course of the study, there were 17 confirmed diagnoses of breast cancer in the low-fat comparison group, 10 in the Mediterranean diet with nuts group and eight in the Mediterranean diet with olive oil group, the researchers found.
Women eating a Mediterranean diet supplemented with EVOO showed a 68 percent relatively lower risk of malignant breast cancer than those allocated to the control diet. Women eating a Mediterranean diet supplemented with nuts showed a non-significant risk reduction compared with women in the control group. (A non-significant finding means it could have occurred by chance.)
There is some evidence with animal studies that extra virgin olive oil, which is rich in polyphenols, may induce programmed cell death or early cancer cells in the breast, the researchers noted.
The study had many limitations, but a Mediterranean diet is safe and has been found to reduce the risk of cardiovascular disease.
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