OLIVE OILS AND HEALTH 174 14.3. Extra virgin olive oil in the prevention and fight against cancer In experimental studies, extra virgin olive oil (EVOO) has been shown to exert preventive effects on the three main diet-related cancers (breast, colorectal, and prostate), with breast cancer being the most extensively studied. The evidence suggests that an appropriate (non-excessive) consumption of EVOO, within the context of a healthy diet and lifestyle, favours prevention and acts against the development of these types of cancer. With respect to breast cancer, the “Multidisciplinary Group for Breast Cancer Studies” (GMECM, “Grupo Multidisciplinario para el Estudio del Cáner de Mama”, “Autonomous University of Barcelona”, Spain) has demonstrated in experimental models that diets in which extra virgin olive oil (EVOO) is the main source of fat slow down tumour cell proliferation and promote their death by apoptosis. Furthermore, when cancer has already developed, the tumours are more differentiated and of a lower degree of malignancy. In addition, when EVOO is a regular dietary habit from an early age, it exerts an effect on sexual maturation compatible with a protective action of the mammary gland against its later transformation into cancer. There is some evidence that this action may be mediated through neuro-endocrine mechanisms, which could also be related to its effects on maintaining body weight. In human studies carried out by the GMECM, there is also the possibility that EVOO exerts some of its favourable effects in women’s breast cancer through the maintenance of the epigenome, although this possibility has not yet been sufficiently demonstrated. These latest investigations have also been conducted in experimental tumours, obtaining a higher degree of scientific evidence. Other groups have later obtained similar results to those demonstrated by the GMECM in experimental cancer. In contrast, in these experimental studies by the GMECM, diets containing an excess of ω-6 lipids markedly stimulate breast cancer, and the resulting tumours are of a high degree of malignancy. Moreover, unlike EVOO, ω-6 fats can act as a co-carcinogen in the initiation of this cancer through xenobiotic detoxification pathways, causing damage to DNA. Other researchers have also reported that saturated lipids have a stimulating effect on this type of cancer. In isolated epidemiological studies, which usually involve a small number of participants, estimates of the beneficial effect of olive oil on breast cancer are not statistically significant, and the level of evidence is very low. However, in studies with a larger number of cases, or when combined in a meta-analysis, this beneficial association becomes evident. A reduction in the risk of breast cancer has also been
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