Olive trees (Olea europea) have been cultivated in the Mediterranean basin for thousands of years. Both the fruit and its oil have been highly valued as a source of food and wealth since ancient times.1

Mediterranean countries continue to be the largest producers of all olive products, with Spain leading the world and Italy close behind.1 As the main fat in the so-called Mediterranean diet, olive oil has come under intense scrutiny in the past decade as a potential reason for the lower incidence of cardiovascular (CV) morbidity and mortality in that region.2

Background

Olive plants vary from shrubs to small trees, and trees are most common for commercial purposes. They produce long clusters of flowers that give way to singlets of immature fruit, which start as dark green and ripen through purple to black. Depending on the desired product, the fruit is harvested by hand at different stages of ripeness.

Olive oil is best extracted from dark brown-black ripe fruit. After washing and cleansing of extraneous debris, the whole olive, including the pit, is ground into a paste and stirred. This process promotes seepage of the oil from the flesh.

The next step is separating the oil from the pulp mix. Modern methods employ either a mechanized press or high-speed centrifugation.3 The oil extracted by the first pass of pulp through the press or centrifuge is known as extra virgin olive oil. It contains more fatty acids and polyphenols when compared with other types of oil.4 Subsequent presses continue to yield food-grade oil, but they contain fewer of the fatty acids and phenols.

Evidence of effectiveness

Perhaps the best evidence of effectiveness is the FDA’s 2004 approval for labeling olive oil as a nonpharmaceutical product that reduces the risk of coronary heart disease.5

Chemically, olive oil is composed mostly of monounsaturated fatty acids (MUFAs).2,6 Research examining its potential CV benefits centers on comparing metabolism of MUFAs with polyunsaturated fats, which are more common in the Western diet.

One established risk factor for atherosclerotic disease is postprandial fat content in the blood. Olive oil has been shown in several studies to not only reduce this after-meal lipemia, but also to promote more rapid metabolism of the damaging, oxidative chylomicrons formed after eating fats.2,6 Not only does this process help to reduce the formation of LDL, but it increases production of HDL and reduces the cell-damaging oxidative process.2

This antioxidant property of olive oil gives rise to studies of other major diseases, including cancer. Once again, epidemiologic data tell us that the people of the Mediterranean basin have lower incidences of breast, skin, and colon cancers.4,7

Researchers have concluded that oxidative damage to proteins, DNA, and lipids is a major contributor to the development of malignant cell growth. Therefore, any food with antioxidant actions is of interest as a possible deterrent in this process. In addition to the MUFAs, another group of antioxidants found in olive oil is the polyphenols. Assays of extra virgin olive oil have shown phenolic contents to reach 500 mg/kg. These phenols act in vivo to inhibit angiogenesis and stabilize cell structure, both deterrents to neoplasmic activity.4

Olive oil also exerts antimicrobial activity on Helicobacter pylori in the duodenum.8 Again, this benefit appears to be based on the antioxidant and cellular stabilization capacities of olive oil. The phenols in the olive oil have been shown in vitro to actually diffuse into the gastric lining cells where it kills these bacteria.

Other studies regarding the potential of olive oil’s benefits on inflammatory conditions are examining rheumatoid arthritis. In 2005 researchers discovered that extra virgin olive oil  contains a compound known as oleocanthol, which exerts a COX-1 and COX-2 inhibitory effect similar to that of ibuprofen. Although chemically very different, the anti-inflammatory effect seems very promising.9

Safety and drug interaction

Because olive oil is a botanical product, allergic reactions are always a possibility. Skin-patch testing for individuals with significant atopic histories is advised. While there are no known drug interactions, highly antioxidant compounds can increase the potency of warfarin, so patients using this anticoagulant are advised to proceed with caution. 

Dose

 
Herein lies the question: Which kind of olive oil is best? Most studies are conducted with extra virgin olive oil using a daily intake of 1 to 2 oz, or 30 to 60 mL. This is the amount typically found in salad dressings, cooking, and spreads.

Multiple assays have verified that extra virgin olive oil contains the highest concentration of MUFAs and polyphenols,10 but it is also the most expensive type of olive oil. Other less costly grades are still quite healthful but less effective.

Summary

Considering the amount of attention that we as practitioners pay to lipid profiles and other forms of antioxidant protection in prescription pharmaceuticals, ignoring so readily available, tasty, and effective an alternative as olive oil is quite an oversight. Clinicians need to start encouraging patients to use it whenever possible in their cooking.

References

1. The Olive Oil Source. The history of the olive tree. 2008.
2. Covas MI. Olive oil and the cardiovascular system. Pharmacol Res. 2007;55:175-186.
3. The Olive Oil Source. How olives are turned into oil. 2008.
4. Waterman E, Lockwood B. Active components and clinical applications of olive oil. Altern Med Rev. 2007;12:331-342.
5. FDA allows qualified health claim to decrease risk of coronary heart disease [press release]. Washington, D.C.: FDA; November 1, 2004.
6. Ruano J, López-Miranda J, de la Torre R, et al. Intake of phenol-rich virgin olive oil improves the postprandial prothrombotic profile in hypercholesterolemic patients. Am J Clin Nutr. 2007;86:341-346.
7. Owen RW, Giacosa A, Hull WE, et al. Olive-oil consumption and health: the possible role of antioxidants. Lancet Oncol. 2000;1:107-112.
8. Romero C, Medina E, Vargas J, et al. In vitro activity of olive oil polyphenols against Helicobacter pylori. J Agric Food Chem. 2007;55:680-686.
9. Beauchamp GK, Keast RS, Morel D, et al. Phytochemistry: ibuprofen-like activity in extra-virgin olive oil. Nature. 2005;437:45-46.
10. International Olive Council. Designations and definitions of olive oils.

All electronic documents accessed July 14, 2009.