Researchers looked at data from the PREDIMED study of more than 4,000 women, originally designed to investigate the effect of a Mediterranean diet (MeDiet) on cardiovascular disease – but which also recorded incidences of cancer and other outcomes. Three groups of participants consumed a MeDiet with nuts, a MeDiet with extra-virgin olive oil (EVOO), or, for a control group, no specified diet, but with advice to reduce fat consumption.
15% of calories from EVOO
“In this secondary analysis of the PREDIMED trial, we found a significant inverse association between consumption of a MeDiet supplemented with EVOO and breast cancer incidence. A high consumption of EVOO (≥15% of total energy intake) seems to be instrumental for obtaining this significant protection,” wrote the authors of the new analysis, in a paper published in the journalJAMA Internal Medicine.
“Women allocated to the MeDiet supplemented with EVOO showed a 62% relatively lower risk of malignant breast cancer than those allocated to the control diet. Participants in the MeDiet supplemented with nuts showed a nonsignificant risk reduction compared with women in the control group,” they added.
However, as the PREDIMED trial only saw 35 confirmed instances of breast cancer, the study authors suggested their conclusions should be confirmed by long-term studies covering more incident cases of breast cancer.
EVOO, or just olive oil?
They also noted there is a scarcity of studies looking at the relationship between EVOO and cancers in general, including breast cancer. One meta-analysis does suggest olive oil consumption – including EVOO – is inversely associated with breast cancer incidence, but the researchers noted EVOO includes a number of compounds which might make it more effective at preventing cancer.
“Several biological mechanisms could explain the putative anticarcinogenic properties of EVOO. All types of olive oil provide a high supply of monounsaturated fatty acids, mainly oleic acid, as well as squalene, whereas EVOO also contains various biologically active compounds, such as the polyphenols oleocanthal, oleuropein, hydroxytyrosol, and lignans,” the authors wrote.
On the relationship between the MeDiet and breast cancer, they noted: “No prior nutrition intervention trial has addressed the effect of the MeDiet specifically on breast cancer. In the Lyon Diet Heart Study, a randomised trial, a protective effect of a cardioprotective Mediterranean-type diet against overall cancer incidence was observed, supporting the hypothesis of an anticancer effect of the MeDiet.
“The results of the PREDIMED trial suggest a beneficial effect of a MeDiet supplemented with EVOO in the primary prevention of breast cancer. Preventive strategies represent the most sensible approach against cancer,” the authors concluded.
Source: JAMA Internal Medicine
Published online ahead of print,doi:10.1001/jamainternmed.2015.4838
“Mediterranean Diet and Invasive Breast Cancer Risk Among Women at High Cardiovascular Risk in the PREDIMED Trial”
Authors: E. Toledo; J. Salas-Salvadó; C. Donat-Vargas; P. Buil-Cosiales; R. Estruch; E. Ros; D. Corella; M. Fitó; F. B. Hu; F. Arós; E. Gómez-Gracia; D. Romaguera; M. Ortega-Calvo; L. Serra-Majem; X. Pintó; H. Schröder; J. Basora; J. Vicente Sorlí; M. Bulló; M. Serra-Mir; M. A. Martínez-González