Olives and olive oil are recommended for breast cancer
Olive oil is a major source phytochemicals, including single phenols, phenolic acids, lignans, flavonoids, and secoiridoids, some of which have been found to be chemopreventive. Olive oil is a major dietary source of oleic acid (a monounsaturated fatty acid) and also contains squalene, lupeol and melatonin. When isolated from olive oil, oleic acid has been shown to have chemopreventive effects but it has also been shown to promote the growth of breast cancer cells in the laboratory. Olive oil has been shown to reduce oxidative DNA damage and improve coronary heart disease by reducing blood pressure, low-density lipoprotein (LDL) cholesterol, and inflammation. Olive oil consumption was shown to be significantly related to less cognitive decline in one study of 8,028 French subjects aged 65 years and over, and has been shown to reduce pain and disability in those with arthritis. Olive extract has been shown to inhibit proliferation and induce cell death of gastric cancer, lung cancer, and leukemia cells. Olive oil consumption also has been associated with lower risks of colon and ovarian cancer.
Breast cancer-related effects of consuming olives and olive oil
A number of studies have found that olive oil consumption (and monounsaturated oil consumption generally) is associated with a lower risk of breast cancer. For example, a prospective Swedish study found a lower risk of breast cancer for women after 50 with a high intake of monounsaturated fat compared to consumption of other types of fat. A study of women in the Canary Islands found a lower risk of breast cancer for women in the highest quintile of monounsaturated fat consumption and even lower for those consuming mostly olive oil. Italian and Greek studies have also found that olive oil consumption is associated with a lower risk of breast cancer. Oleic acid has been shown to increase the effect of the chemotherapy drug Taxol (paclitaxel) against breast cancer.
Numerous studies have found that extra virgin olive oil inhibits proliferation of and induces apoptosis of HER2 overexpressing breast cancer cells. These effects appear to be due to olive lignans and secoiridoids rather than olive phenols and phenolic acids. In fact, some observers have concluded that the protective effect of olive oil against breast cancer is mostly confined to the HER2-positive breast cancer subtype, with no significant influence on the occurrence of HER2-negative breast cancers.
Additional comments
Oleic acid has been shown to increase the bioavailability of beta-carotene in the diet, which may help explain why the high raw vegetable/high olive oil dietary pattern appears to be protective against breast cancer. Emphasizing monounsaturated fats in the diet is thought to have a positive effect on health in part because it will help reduce the relative proportions of saturated fats, trans fatty acids and omega-6 fatty acids in the diet. Adding olive oil to the typical American diet by using it to fry with or to make marinades or pasta sauces is unlikely to have as much positive impact on breast cancer risk as would using olive oil in salad dressings and to prepare dishes with a high proportion of vegetables.