Olive oil

Should I cease giving my oil, with which they honor God and men?” Judges 9:9

Olive oil has been used in food preparation and for other purposes, such as in olive lamps or as an ointment, since the ancient times. In the Bible, olive oil is mentioned as a blessing for those consuming it. In the Book of Deuteronomy we read God pledge regarding the Promise Land: “For the Lord your God is bringing you into a good land, a land of brooks of water, of fountains and springs, that flow out of valleys and hills; a land of wheat and barley, of vines and fig trees and pomegranates, a land of olive oil and honey; (…).” It is very likely that olive oil was used in preparation of manna, as alluded to in the following passage: “Now the manna was like coriander seed, and its color like the color of bdellium. The people went about and gathered it, ground it on millstones or beat it in the mortar, cooked it in pans, and made cakes of it; and its taste was like the taste of pastry prepared with oil.” In biblical time, olive oil was derived by crushing olives with large stones, collecting the crushed olives and placing them under large stone to be squeezed. Olive oil would then flow into a basin below the crushing and squeezing area. The pictures below show a method of crushing olives (on the left) and stones used to squeeze the olives (on the right) in ancient Israel to derive olive oil.

Nutritional profile of olive oil

Olive oil contains mainly mono-unsaturated fatty acids. In one tablespoon of extra virgin olive oil, there are 10 grams of mono, 2 grams of saturated and 2 grams of polyunsaturated fatty acids. Olive oil is also a relatively good source of two fat-soluble vitamins, vitamin E and K, providing approximately 10 percent of daily value per tablespoon. In addition to the fatty acid content, olive oil contains a variety of compounds called the phenolic compounds. In fact, no less than 66 different phenolic compounds have been identified. Phenolic compounds, among other things, influence the color and taste of given foods. Many health effects of olive oil have been attributed more so to its phenolic compounds content than its composition of different type of fatty acids. Several factors play a role in the content of these beneficial compounds in olive oil. They include the type of cultivar used, region where the trees are grown, age of the trees, olive storage conditions, stage of maturation of olives, type of processing, storage conditions and heat. The phenolic compounds found in olive oil have been shown to have anti-oxidative, anti-inflammatory, anti-microbial, and anti-carcinogenic activities.

What are the health effects of olive oil?     

Of all the oils available in grocery stores, olive oil is one of the most beneficial to human health. Research clearly shows that the use of olive oil helps in reducing the risk of many chronic diseases such as heart disease, cancer, stroke, and hypertension. For example, a study published in the medical journal Archives of Internal Medicine showed that olive oil is effective in reducing blood pressure. In this experiment, patients were divided into two groups. One group was instructed to add olive oil (men 4 tablespoons and women 3 tablespoons) to their diet and the other group was advised to add the same amount of sunflower seed oil. After 6 months, 8 of the11 patients who consumed olive oil no longer needed to take antihypertensive medications. However, none of those ingesting the sunflower seed oil discontinued using medications.

In a large Italian study with 29,689 women, who were followed for almost 8 years, those with the highest intake of olive oil, compared to those with the lowest intake had a statistically significant 44 percent lower risk of coronary heart disease. In another study with over 40,000 participants from Spain, intake of each 10 grams (about 1/3 of an ounce) of olive oil was associated with 7 percent lower risk of coronary heart disease risk. Consequently, experts on the health effects of olive oil state that, “exclusive use of olive oil during food preparation seems to offer significant protection against CHD (coronary heart disease – author), irrespective of various clinical, lifestyle and other characteristics of the participants.”

Research findings also indicate that olive oil can help to reduce risk of some types of cancer. One such study was carried out with 755 women living in the Canary Islands. The women, who consumed the highest amount of olive oil, had a 48 percent lower risk of developing breast cancer compared to women consuming the least amount of olive oil. A study conducted in Italy and Switzerland, assessed the impact of olive oil consumption on risk of developing cancer of the colon (large intestine) and rectum. In this research, scientists assessed risk based on the amount of olive oil used in frying. From other studies, it is known that carcinogenic compounds (e.g. oxygen radicals) can develop when fats and/or oils are heated to a high temperature. Researchers compare the risk among 886 individuals with to 4,765 individuals without cancer. The results indicated that olive oil users had a reduced cancer risk by 11 percent.

Another study conducted in Greece showed that those with the greatest long-term consumption of olive oil (consumption of almost every day in a lifetime) had about 4 times lower risk of developing arthritis compared to those who consumed olive oil, on average, only about six times per month. The same researchers showed that increasing the consumption of olive oil to two times a week, reduced the risk of developing arthritis by half. Olive oil may also offer some protection against bone fractures. A study published in the European Journal of Clinical Nutrition conducted in Spain showed that people who had the greatest ratio of olive oil to omega-6 had an 80 percent reduced risk of fractures.

At a conference about the impact of olive oil on human health held in Cordoba in Spain, an organization, the Centro de Excelencia Foundation sobre Aceite de Oliva y Salud stated that the use of olive oil reduces the risk of cardiovascular disease, probably protects against age-related decline in cognitive abilities and Alzheimer’s disease, is associated with healthier aging and longevity. In the conference’s report we also read: “The protective effect of virgin olive oil can be most important in the first decades of life, which suggests that the dietetic benefit of virgin olive oil intake should be initiated before puberty, and maintained through life.” Additionally, according to the recommendations of the Advisory Committee of the American Heart Association, “a diet high in MUFA (monounsaturated fatty acids, olive oil predominantly contains this type of fat – author) (versus a high-carbohydrate diet) improves glycemic control in individuals with NIDDM (none-insulin dependent diabetes mellitus – author) who maintain body weight. Individuals with elevated triglycerides or insulin levels also may benefit from a high-MUFA diet.”

Is it true that olive oil detrimentally impacts arterial walls?

In recent years, some prominent advocates of vegan diets made a claim that the use of virgin olive oil detrimentally effects the epithelial cells of arteries, thus, increasing risk of atherosclerosis. For that reason, the same individuals advocate the use of virtually no oil of any kind, including no olive oil in cooking or food preparation. Arterial walls are composed of three distinct layers. The most inner of these layers is called intima. This layer is lined with specialized epithelial cells called endothelial cells also referred to as the endothelium. The structure of arteries is illustrated below.

When endothelium gets damaged or when the endothelial cells die the atherosclerotic process begins. Any factor that damages or cause these cells to die may increase risk of cardiovascular disease. Damage endothelium triggers inflammatory reaction (as is the case with any cuts on a skin). Scientists are able to measure a degree of inflammation by assessing the levels of such compounds as C-reactive protein and cytokines (mainly a specific type of cytokines called interleukin-6).

The claim that virgin olive oil damages the endothelium is based on selectively picked findings. To date, a number of studies assessed the impact of olive oil on arterial function and structure. In 2015, a team of scientists from Austria and Germany published a meta-analysis of findings from 30 different studies based on 3,106 participants. A meta-analysis is a specific tool scientists use to evaluate and summarize findings of more than one studies in order to assess their combined effect. The following is the conclusion these scientist reached: “Olive oil interventions (with daily consumption ranging approximately between 5 to 50 g) resulted in a significantly more pronounced decrease in C-reactive protein (mean difference: -0.64 mg/L, (95% confidence interval (CI) -0.96 to -0.31), p < 0.0001, n = 15 trials) and interleukin-6 (mean difference: -0.29 (95% CI -0.7 to -0.02), p < 0.04, n = 7 trials) as compared to controls, respectively.” A decrease in either C-reactive protein or interleukin-6 indicates a lower level of inflammation, which means healthier endothelium, better arterial function and lower risk of heart disease.

Similarly, scientists are capable of assessing the function of arteries by measuring how much blood is able to flow through them. Lower blood flow usually indicates a narrowing of arteries due to plaque formation inside arterial wall. Assessment of blood flow is referred to as “flow-mediated dilatation” also sometimes called “flow-mediated vasodilatation.” In the above-mentioned meta-analysis, authors stated that, “Values of flow-mediated dilatation (given as absolute percentage) were significantly more increased in individuals subjected to olive oil interventions (mean difference: 0.76% (95% CI 0.27 to 1.24), p < 0.002, n = 8 trials).” An increase of blood flow indicates less atherosclerosis in the arteries and wider arterial lumen. Consequently, these researchers stated, that, “These results provide evidence that olive oil might exert beneficial effects on endothelial function as well as markers of inflammation and endothelial function, thus representing a key ingredient contributing to the cardiovascular-protective effects of a Mediterranean diet.” Thus, a conclusion that olive oil damages arterial endothelium is inconsistent with the best available evidence.

Is it true to olive oil should not be heated?

One of the most common questions asked about olive oil is regarding its use in frying and baking. This is because in some sources, including many websites, one can find information that olive oil should not be used for frying or baking due to the fact that this oil has relatively low smoking and burning temperatures. According to the International Olive Oil Council the smoke temperature of olive oil is 210 degrees C (410oF), and according to the Institute of Shortening and Edible Oils, it is 215 degrees C (420oF). In comparison, the smoke temperature of canola seed oil is approximately 205 degrees (400oF). Smoke temperature of oils and fats has been known for many decades. In 1940, two scholars, Detwiler and Markley, published oil burning temperatures in the Journal of the American Oil Chemists Society. The smoke and burning temperatures of selected oils are included in the table below. The values are based on the above mentioned publication.

As can be seen from values found in the table, smoke and burning temperatures of olive oil are comparable to those of other commonly used oils. Based on this data, it can be concluded that olive oil can be used in place of other vegetable oils for frying, baking and other kind of food preparation.

Table 1. The smoke and burning temperatures of selected oils.

OilSmoke temperature 0°C 0°FBurning temperature 0°C 0°F
Virgin olive oil199 (390°F)361 (682°F)
Flax seeds oil163 (325°F)353 (667°F)
Corn Oil227 (441°F)359 (678°F)
Soybean Oil194 (381°F)361 (682°F)

There are several types of olive oil available in grocery stores. Several types of olive oils are listed and described in the table below. The main difference between them has to do with the production method of these oils. The process of production also effects the content of bioactive compounds found in these oils. Similarly, the olive oils differ somewhat in terms of the chemical structure of the oil. In nature, the bulk of fats and oils come in a form of triglycerides. Triglycerides are compounds composed of a glycerol backbone with three attached fatty acids. A simplified structure of triglycerides is depicted below.

What is the difference between olive oil and extra virgin olive oil?

Due to the exposure to environmental factors, such as temperature or sunshine, fatty acids may get detached from the glycerol backbone. The more fatty acids get detached from glycerol the more acid the oil becomes (the acidification of the oil is called rancidity). The term “virgin” means that it has been derived by mechanical pressing of olives without any use of chemicals or temperature. The term “extra” as in “extra virgin” refers to the oil’s acidity or the content of free floating (detached from glycerol) fatty acids. Thus, an “extra virgin olive oil” means that the oil was obtained by mechanical pressing of olives without the use of temperature or solvents. It also means that it has lower acidity that virgin olive oil and higher acidity than extra, extra virgin olive oil. The health effects of olive oil described above refer to olive oil that has been obtained by mechanical pressing (e.g. virgin olive oil, extra virgin olive oil, etc.). Olive oil that has been obtained by heat and/or the use of chemical solvents may not have the same health effects mainly due to lower content of phenolic compounds. The table below contains a list of different types of olive oils available in grocery stores along with their description.

Table 2. Characteristics of different types of olive oil.

TYPESDESCRIPTION
Virgin Olive OilOlive oil made by mechanical pressing of olives without the use of heat or chemicals, it has a little more free fatty acid content than extra virgin olive oil
Extra Virgin Olive OilOlive oil made by mechanical pressing of olives without the use of heat or chemicals, it has less content of free fatty acids compared to virgin olive oil but more than extra, extra virgin olive oil
Extra Extra Virgin Olive OilOlive oil made by mechanical pressing of olives without the use of heat or chemicals, it has less content of free fatty acids compared to extra virgin olive oil but more than extra, extra, extra virgin olive oil
Extra Extra Extra Virgin Olive OilThe best type with the fewest fatty acids detached from glycerol
Lite Olive OilRefined oil with less distinguish taste
Refined Olive OilMade with the use of heat and chemicals from leftover olives pulp from the production of virgin olive oil
Pure Olive OilThis type of oil is usually a mixture of virgin and refined olive oil, the latter being derived with heat and with chemical compounds
Pomace Olive OilThis type of oil is usually a mixture of virgin and refined olive oil, the latter being derived with heat and with chemical compounds

Summary and recommendations

Virgin olive oil has been used in food preparation since the ancient time. Virgin olive oil offers several health benefits including lower risk of cardiovascular disease and reduced risk of some cancers. These benefits are a result of nutritional profile of olive oil, mainly the content of phenolic compounds. Olive oil enhances flavor of food and it can be used raw and in cooking, baking or frying. Although olive oil is considerably more expensive than most other types of plant-derived oils, since it offers health benefits that are not obtained by using other types of oils, it seems like its use is a good investment in our health.

 

Roman Pawlak, Ph.D, RD

Associate Professor

Department of Nutrition Science

East Carolina University

 

Selected references

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Detwiler S., Markley K. Smoke, flash, and fire points of soybean and other vegetable oils. U.S. regional soybean industrial products laboratory. Urbana, IL.

Dybkowska E., Waszkiewicz-Robak B., Świderski F. Assessment of n-3 and n-6 polyunsaturated fatty acid intake in the average Polish diet. Polish Journal of Food and Nutrition Science, 2004;13/54(4):409–414.

Ferrara A., Raimondi S., d’Episcopo L., Guida L., Russo A., Marotta T. Olive Oil and Reduced Need for Antihypertensive Medications. Archives of Internal Medicine, 2000;160:837-842.

Garcia-Segovia P, Sanchez-Villegas A, Doreste J. Olive oil consumption and risk of breast cancer in the Canary Islands: A population-based case-controlled study. Public Health Nutrition, 2006;9(1A):163-167.

Galeone C., Talamini R., Levi F., Pelucchi C., Negri E., Giacosa A., Montella M., Franceschi S., Vecchia C. Fried foods, olive oil and colorectal cancer. Annals of Oncology, 2007;18(1):36-39.

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Kalmijn S., Launer L., Ott A., Witteman J., Hofman A., Breteler M. Dietarv Fat Intake and the Risk of Incident Dementia in the Rotterdam Study. Annals of Neurology, 1997;42:776-782.

Kontogianni M., Panagiotakos D., Chrysohoou C., Pitsavos C., Zampelas A., Stefanadis C. The impact of olive oil consumption pattern on the risk of acute coronary syndromes: The CARDIO2000 case-control study. Clinical Cardiology, 2007;30 (3):125-129.

Kris-Etherton P. Monounsaturated Fatty Acids and Risk of Cardiovascular Disease. Circulation, 1999;100:1253-1258.

Linos A., Kaklamanis E., Kontomerkos A., Koumantaki Y., Gazi S., Vaiopoulos G., Tsokos G. Kaklamanis P. The effect of olive oil and fish consumption on rheumatoid arthritis – a case control study. Scandinavian Journal of Rheumatology, 1991;20(6):419-426.

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