Mediterranean diet plus olive oil associated with reduced breast cancer risk
The JAMA Network Journals
Breast
cancer is a frequently diagnosed cancer and a leading cause of death in women.
Diet has been extensively studied as a modifiable risk factor in the
development of breast cancer but epidemiologic evidence on the effect of
specific dietary factors is inconsistent.
The Mediterranean diet is known for its abundance of plant foods, fish and especially olive oil.
Miguel A. Martínez-González, M.D., of the University of Navarra in Pamplona and CIBEROBN in Madrid, Spain, and coauthors analyzed the effects of two interventions with the Mediterranean diet (supplemented with extra virgin olive oil [EVOO] or nuts) compared with advice to women to follow a low-fat diet.
Study participants in the two intervention groups were given
EVOO (one liter per week for the participants and their families) or mixed nuts
(30 grams per day: 15 grams of walnuts, 7.5 grams of hazelnuts and 7.5 grams of
almonds).
The
study was conducted within the framework of the large PREDIMED (Prevención con
Dieta Mediterránea) trial, which was designed to test the effects of the
Mediterranean diet on the primary prevention of cardiovascular disease.
From
2003 to 2009, 4,282 women (ages 60 to 80 and at high risk of cardiovascular
disease) were recruited. Women were randomly assigned to the Mediterranean diet
supplemented with EVOO (n=1,476), the Mediterranean diet supplemented with nuts
(n=1,285) or the control diet with advice to reduce their dietary intake of fat
(n=1,391).
The
women were an average age of 67.7 years old, had an average body mass index of
30.4, most of them had undergone menopause before the age of 55 and less than 3
percent used hormone therapy. During a median follow-up of nearly five years,
the authors identified 35 confirmed incident (new) cases of malignant breast
cancer.
The
authors report that women eating a Mediterranean diet supplemented with EVOO
showed a 68 percent (multivariable-adjusted hazard ratio of 0.32) relatively
lower risk of malignant breast cancer than those allocated to the control diet.
Women eating a Mediterranean diet supplemented with nuts showed a
nonsignificant risk reduction compared with women in the control group.
The
authors note a number of limitations in their study including that breast
cancer was not the primary end point of the trial for which the women were
recruited; the number of observed breast cancer cases was low; the authors do
not have information on an individual basis on whether and when women in the trial
underwent mammography; and the study cannot establish whether the observed
beneficial effect was attributable mainly to the EVOO or to its consumption
within the context of the Mediterranean diet.
"The results of the PREDIMED trial suggest a beneficial effect of a MeDiet [Mediterranean diet] supplemented with EVOO in the primary prevention of breast cancer. Preventive strategies represent the most sensible approach against cancer.
"The intervention paradigm implemented in the PREDIMED trial provides a useful scenario for breast cancer prevention because it is conducted in primary health care centers and also offers beneficial effects on a wide variety of health outcomes. Nevertheless, these results need confirmation by long-term studies with a higher number of incident cases," the authors conclude.