Olive oil is a mostly unsaturated oil consisting primarily of oleic acid (an omega-9 monounsaturated fatty acid), linoleic acid (an omega-6 fatty acid), palmitic acid, and stearic acid. In addition, olive oil is a significant source of lupeol, luteolin, and oleanolic acid. 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. Oleic acid does not appear to account for its anti-cancer effects and in fact might promote breast cancer. While oleic acid has anti-inflammatory properties, it has also been shown to induce migration and proliferation of both hormone receptor positive (ER+/PR+) and triple negative breast cancer cells. These findings imply that the protective effect of olive oil are due to other components of the oil and not the direct effect of oleic acid. The findings also argue against using highly refined olive oil.
Extra-virgin olive oil contains at least 30 phenolic compounds, a diverse group of aromatic compounds. Included are some familiar flavonoids such as luteolin and phenolic acids such as caffeic acid, gallic acid, p-coumaric acid, vanillic acid, and ferulic acid. However, the most important phenolic compounds include the less familiar oleuropein, oleocanthal, hydroxytyrosol, and tyrosol. Black olives also contain rutin, which may reduce the cardiotoxic effects of Adriamycin, as well as cyanidin-3-glucoside, which has been shown to possess both chemopreventive and chemotherapeutic activity and to enhance the treatment effects of Herceptin. The phenolic compounds present in olive oil are strong antioxidants and free radical scavengers and have been shown to have anti-cancer effects in breast cancer cells. This again highlights the importance of using extra-virgin olive oil (from the first pressing) rather than later pressings or more processed and refined olive oil, which tend to have less or very little phenolic content.
Breast cancer-related effects of consuming olives and olive oil
Most population studies have found link between olive oil and lower breast cancer risk
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. A 2011 meta-analysis of data from 19 previous case-control studies found that the highest level of olive oil consumption was associated with approximately half the risk of developing breast cancer compared with the lowest intake level of intake. On the other hand, a large 2012 prospective study among women in Spain, Italy and Greece reported that women in the highest third of olive oil consumption had essentially the same risk of breast cancer as those in the lowest third.
Olive oil may reduce HER2+ risk preferentially
Numerous studies have found that extra virgin olive oil inhibits proliferation of and induces apoptosis of HER2/neu overexpressing (HER2+) 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+ breast cancer subtype, with no significant influence on the occurrence of HER2- disease.
Olive oil consumption may reduce aggressiveness of breast cancer that does develop
Consumption of olive oil reduces the aggressiveness of mammary tumors in animal models of breast cancer. One study compared induced tumors in rats that were fed high-fat diets — either olive oil or corn oil. The high corn oil diet clearly stimulated cancer development, resulting in the earliest appearance of tumors and the highest tumor incidence and yield, whereas the high extra-virgin olive oil diet appeared to have only a weak enhancing effect, primarily by increasing tumor yield compared to control animals fed a low-fat diet.
Laboratory studies have documented specific olive oil-induced molecular changes in cancer cells and tumors, including changes in the composition of cell membranes, signaling proteins and gene expression. These changes are likely to result in lower proliferation and more apoptosis (programmed cell death) of breast cancer cells, as well as enhanced protection against DNA damage.
Olive oil enhances treatment effects of aromatase inhibitors, Taxol, and Herceptin
Extra-virgin olive oil potentiates the effects of aromatase inhibitors in ER+/PR+ breast cancer cells by increasing programmed cell death. Oleic acid has been shown to increase the effect of the chemotherapy drug Taxol (paclitaxel) against breast cancer. Olive oil has also been shown to increase Herceptin effectiveness in treating HER2+ breast cancer and may counteract resistance to Herceptin.
Consumption of olive oil was associated with lower breast density, a strong breast cancer risk factor, in one study. 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 extra-virgin 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.
Below are links to recent studies concerning this food. For a more complete list, including less recent studies, please click on olives.