Dietary fat, both in terms of quantity and quality, has been implicated to
cancer development, either positively or negatively. The aim of this work was to evaluate whether
olive oil or monounsaturated fat intake was associated with the development of
cancer. A systematic search of relevant studies, published in English, between 1990 and March 1, 2011, was performed through a computer-assisted literature tool (i.e., Pubmed). In total 38 studies were initially allocated; of them 19 case-control studies were finally studied (13800
cancer patients and 23340 controls were included). Random effects meta-analysis was applied in order to evaluate the research hypothesis. It was found that compared with the lowest, the highest category of
olive oil consumption was associated with lower odds of having any type of
cancer (log odds ratio = -0.41, 95%CI -0.53, -0.29, Cohran's Q = 47.52, p = 0.0002, I-sq = 62%); the latter was irrespective of the country of origin (Mediterranean or non-Mediterranean). Moreover,
olive oil consumption was associated with lower odds of developing
breast cancer (logOR = -0,45 95%CI -0.78 to -0.12), and a
cancer of the digestive system (logOR = -0,36 95%CI -0.50 to -0.21), compared with the lowest intake. The strength and consistency of the findings states a hypothesis about the protective role of
olive oil intake on
cancer risk. However, it is still unclear whether
olive oil's
monounsaturated fatty acid content or its
antioxidant components are responsible for its beneficial effects.