`Med Diet with Extra Virgin Olive Oil Reduces Incidence of Invasive Breast Cancer


Med Diet with Extra Virgin Olive Oil Reduces Incidence of Invasive Breast Cancer

Feb. 24, 2016
Jedha Dening

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For women, breast can­cer is the most fre­quently diag­nosed malig­nant tumor and is the lead­ing cause of death among women. Since 2008, breast can­cer inci­dence world­wide has increased by more than 20 per­cent and mor­tal­ity from breast can­cer has increased by 14 per­cent.

His­tor­i­cally breast can­cer rates have been lower in North­ern or Cen­tral Euro­pean coun­tries where the Mediter­ranean diet (Med­Diet) is com­monly con­sumed. The Med­Diet is char­ac­ter­ized by an abun­dance of plant foods, fish, and the con­sump­tion of extra vir­gin olive oil (EVOO). Numer­ous prospec­tive cohort stud­ies have eval­u­ated the asso­ci­a­tion between the Med­Diet and breast can­cer risk, but results have often been lim­ited and con­flict­ing. Until recently (Sept 2015) there has never been a ran­dom­ized con­trol trial to help estab­lish more solid evi­dence.

The study by Toledo and Col­leagues, pub­lished in JAMA Inter­nal Med­i­cine, was con­ducted in the frame­work of the Pred­imed trial. The Pred­imed trial was a Span­ish mul­ti­cen­ter ran­dom­ized sin­gle blind con­trolled trial.

The sub­analy­sis done by Toledo and Col­leagues took 4,282 post­menopausal women out of the 7,447 par­tic­i­pants in the Pred­imed trial. Women were aged 60 to 80 years and 4,152 of the 4,282 had no pre­vi­ous his­tory of breast can­cer. There were three lines of ran­dom­ized dietary rec­om­men­da­tions, a Med­Diet sup­ple­mented with EVOO, a Med­Diet sup­ple­mented with nuts and a con­trol group fol­low­ing gen­eral low-fat dietary advice.

Accord­ing to Hoff­man and Schwing­shackl, pro­vid­ing com­men­tary on the Toledo trial in Evi­dence Based Med­i­cine, Inva­sive breast can­cer was pre­spec­i­fied as a sec­ondary out­come.” There was an aver­age fol­low-up of 4.8 years with 35 new cases of malig­nant breast can­cer iden­ti­fied by med­ical records or death cer­tifi­cates.


Incred­i­bly, the results of the sec­ondary analy­sis revealed that the risk of inva­sive breast can­cer was reduced by 68 per­cent in those that con­sumed the Med­Diet sup­ple­mented with EVOO. Whereas, there was no such reported effect for the Med­Diet sup­ple­mented with nuts or the con­trol group. It was estab­lished that every addi­tional 5 per­cent of calo­ries con­sumed from EVOO reduced risk of inva­sive breast can­cer by approx­i­mately 28 per­cent.

Accord­ing to Hoff­man and Schwing­shackl, although there is ample evi­dence around the ben­e­fi­cial effects of olive oil for can­cer pre­ven­tion, much of the research is obser­va­tional evi­dence. Hoff­man says, a dis­tin­guish­ing fea­ture of the study by Toledo and co-work­ers is the fact that it is a ran­dom­ized con­trolled trial (RCT). More pre­cisely, it is the first RCT demon­strat­ing the ben­e­fit of a MedD pat­tern on breast can­cer inci­dence.”

One lim­i­ta­tion is that breast can­cer was not a pri­mary out­come of the Pred­imed trial. How­ever, given the large sam­ple size, the ran­dom­iza­tion was able to pro­vide well-bal­anced and com­pa­ra­ble groups, even larger in num­ber than many other tri­als based on mea­sur­ing spe­cific pri­mary out­comes. If any­thing the authors sug­gest that the results of their sub­analy­sis are under­es­ti­mated, sug­gest­ing that the low rate of breast can­cer inci­dence in the Pred­imed trial over­all could, in fact, be attrib­uted to the con­sump­tion of a Med­Diet.

One other thing that is not clear, which would be ben­e­fi­cial to explore in fur­ther research, is whether the observed ben­e­fi­cial effect was attrib­ut­able mainly to extra vir­gin olive oil or to its con­sump­tion within the con­text of the tra­di­tional MeDiet.”

Given the nature of this being a ran­dom­ized trial, one of the most pow­er­ful forms of evi­dence, what this research sug­gests is that con­sum­ing a Med­Diet sup­ple­mented with EVOO could pro­vide a favor­able effect, not just in reduc­ing risk as other stud­ies have shown, but in the pri­mary pre­ven­tion of can­cer, espe­cially breast can­cer.

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