Women who eat the so-called Mediterranean diet supplemented with the purest forms of olive oil enjoy a reduced risk of developing breast cancer, a Spanish study has revealed.
Although diet has been widely studied as a modifiable risk factor in the development of breast cancer, the epidemiologic evidence on the effect of specific dietary factors remains inconsistent, the researchers say.
Dr Miguel A Martinez-Gonzalez, of the University of Navarra in Pamplona and CIBEROBN in Madrid, analysed the effects of two interventions with the Mediterranean diet – supplemented with "extra virgin" olive oil or nuts – compared with advice to women to follow a low-fat diet.
A total of 4,282 women, aged 60 to 80 and all at high risk of cardiovascular disease, took part in the study between 2003 and 2009.
They were randomly assigned to the two dietary groups, with 1,476 having their Mediterranean diet supplemented with extra virgin olive oil, while 1,285 had their diet supplemented with nuts. A control group of 1,391 was given advice on how to reduce their dietary intake of fat.
Study participants in the two intervention groups were given one litre of extra virgin olive oil a week for them and their families to consume or a selection of mixed nuts that comprised 30 grams per day: 15 grams of walnuts, 7.5 grams of hazelnuts and 7.5 grams of almonds.
Women who ate a Mediterranean diet supplemented with the extra virgin olive oil showed a 68% (multivariable-adjusted hazard ratio of 0.32) relatively lower risk of malignant breast cancer than those allocated to the control diet.
The women whose diet was supplemented with nuts showed an insignificant risk reduction compared with women in the control group.
Writing in JAMA Internal Medicine, the authors write: “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 centres 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 admit that there were a number of limitations in their study, including the fact that breast cancer was not the primary end point of the trial; the number of observed breast cancer cases was low; and a lack of information whether and when women in the trial underwent mammography.
Katz M et al. Can Diet Prevent Breast Cancer? JAMA Intern Med. Published online 14 September, 2015.doi:10.1001/jamainternmed.2015.4838.
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