Several epidemiological (population-based) studies have found significantly lower rates of death from all causes, particularly heart disease, among those whose dietary habits are closets to traditional Mediterranean diets (rich in plant foods, olive oil and low in saturated animal fats).
Recently, researchers from the University Of Athens School Of Medicine reviewed all of the epidemiological studies which evaluated the association between adherence to a Mediterranean diet and the occurrence of coronary heart disease outcomes. These studies showed that Mediterranean diet adherence resulted in a reduction in the risk of CHD varying from 8% to 45%.
The seven countries study followed approximately 13,000 healthy middle aged men from Europe, Japan and the U.S. for 15 years. Throughout this time, a total of 2,288 of the men had died. Analyses of the participant’s dietary habits revealed that although total fat intake and polyunsaturated fat intake were not significantly correlated with the risk of death, the greatest dietary correlation was the intake of monounsaturated fats.
A recent case-control study in Spain compared the diets of 171 patients who had recently suffered a non-fatal heart attack, with 171 non-heart attack patients of the same age (age-matched controls). The results of this study found that those who consumed the most olive oil had an 82% reduced risk of heart attack compared with those who rarely consumed olive oil.
These studies provide at least some good evidence that adherence to a Mediterranean-like diet low in saturated fats and high in monounsaturated fats, specifically rich in olive oil, may significantly decrease the risk of heart disease.
Discussed below are some of the mechanisms by which Olive oil may exert its cardio-protective effect, such as its ability to lower total and LDL “bad” cholesterol levels, reduce LDL cholesterol oxidation, increase HDL “good” cholesterol levels, inhibit unnecessary blood clotting, exert an anti-inflammatory action and lower blood pressure in hypertensive patients, as well as the potent anti-oxidant properties of olive oils non-fat components such as its phenolic content; particularly higher in the lesser-processed “extra-virgin” olive oil.
Effect of olive oil on total and LDL “bad” cholesterol
Many human clinical trials have shown that replacement of high saturated fat diets for diets high in monounsaturated fats, mostly from olive oil, have resulted in a significant decrease in both total cholesterol (TC) and particularly LDL “bad” cholesterol; the type of cholesterol known to build up in the arteries and cause atherosclerosis; the hardening and narrowing of the arteries that may lead to blockages and coronary heart disease (CHD) or stroke.
These results have been confirmed in studies involving both men and women of varying ages.
Whilst higher levels of LDL cholesterol (also known as “bad” cholesterol) are associated with the development of atherosclerosis and thus increase the risk of cardiovascular disease, higher levels of high density lipoprotein (HDL) cholesterol, also referred to as “good” cholesterol, is associated with a reduced risk of developing cardiovascular disease.
This is because the HDL particles carry cholesterol away from the arteries and back to the liver, whereas LDL particles carry it from the liver and deposit it in the arteries where it causes atherosclerosis and plaque build- up.
Some studies have also shown an increase in HDL “good” cholesterol after olive oil consumption as well as other beneficial effects on blood lipid (fat) levels such as reduction in the levels of apolipoprotein B and beneficial changes in platelet function.
This is important because higher levels of apolipoprotein B are also associated with an increased risk of cardiovascular disease, and blood platelets are also involved in the development of atherosclerosis by stimulating arterial plaque growth when they come in contact with the inner wall of blood vessels.
LDL particles themselves only become a problem when they are taken up by a type of white blood cell found in arterial plaques called macrophages, and become oxidized, forming “foam cells”. When these LDL particles become oxidized and form foam cells, this further stimulates the progression of plaque buildup in arterial walls, hardening and narrowing the arteries.
Therefore, decreasing the amount of LDL particles in the blood is an important means of preventing atherosclerosis development, but trying to limit the amount of oxidization of those LDL particles that are present, is also important. This leads to the next important point.
Diets high in saturated fatty acids (SUFA’s) are known to raise LDL levels whilst diets high in polyunsaturated fatty acids (PUFA’s) and monounsaturated fatty acids (MUFA’s) tend to decrease LDL levels. In fact, a meta-analysis of 27 human trials designed to examine the effect of polyunsaturated and monounsaturated fatty acid rich diets on blood lipid levels found that both types of dietary fats may potentially lower total and LDL cholesterol levels.
The problem with diets high in PUFA’s however, is that although they may decrease the total levels of LDL particles in the blood, they tend to create a higher concentration of polyunsaturated fats within the LDL particles, which in turn increases the amount of LDL oxidation.
This is because PUFA’s are more readily oxidized than MUFA’s due to the higher number of double bonds in their hydrocarbon chains.
Epidemiological studies have not always found a correlation between fat intake and high-blood pressure (hypertension). In regards to olive oil however, a cross-sectional study which compared the fatty acid levels of middle aged men throughout Europe, found that Italian men had significantly higher tissue levels of Oleic acid ( a type of MFA found in olive oil), and also had lower blood pressures.
Most clinical trials have found no difference in blood pressure among normotensive subjects (people with normal blood pressure) when given Mediterranean-type diets.
One trial however found that healthy patients given a diet high in olive oil (40% fat, 22% MUFA) had reductions in blood pressure when compared to those given the National Cholesterol Education Program (NCEP) Step 1 diet (30% fat, 12% MUFA).
Another trial found that giving a diet high in saturated fats to people who were used to consuming a Mediterranean style diet (low in SFA, high in MUFA) significantly increased their blood pressure. When they resumed their normal Mediterranean style diet however, their blood pressure went back to normal.
These studies however examined the effect of olive oil containing diets in normotensive people. The results of a randomized, crossover trial involving 23 hypertensive patients (people with high-blood pressure) who were given different diets over a year, found that extra virgin olive oil significantly decreased the need for anti-hypertensive medications.
It was suggested that this occurs due to the ability of phenolic compounds found in un-processed (extra-virgin) olive oils to enhance nitric oxide (NO) levels. This study provides preliminary evidence that whilst olive oil may not significantly affect blood pressure in normotensive individuals, it may have at least some beneficial effects in patients with high blood pressure.
Olive oil non-fatty acid components
Although it has been speculated that the beneficial effects of a Mediterranean-like diet are due to certain MUFA’s such as Oleic acid in Olive oil, recent investigations have found that the non-fatty acid component of olive oil such as certain phenols, possess beneficial biologic activities that may contribute to the lower incidence of coronary heart disease (CHD) in the Mediterranean area.
This is why Olive oil, particularly “extra virgin olive oil”, may be healthier than other foods and oils high in MUFA’s. In fact, the main peculiarity of extra-virgin olive oil is the presence of remarkable quantities of phenolic compounds which not only provide high stability and strong taste but may be at least in part responsible for extra-virgin olive oils anti-atherogenic potential (the ability to inhibit the development of atherosclerotic plaques).
Laboratory studies have also shown anti-inflammatory effects of olive oil. Rats fed virgin olive oil had less inflammation when injected with carrageenan (a substance used to induce arthritis) than what rats fed other oils did. Moreover, the rats fed virgin olive oil with an added phenolic component (similar to that found in extra virgin olive oil) had even less inflammation.
A similar study found that both the “un-saponifiable fraction" (non-fat portion) of virgin olive oil including beta-sitosterol and erythrodiol, as well as its phenolic compounds oleuropein, tyrosol, hydroxytyrosol and caffeic acid, all exerted a significant anti-inflammatory effect almost as effective as the anti-inflammatory drug indomethacin (an NSAID) did.
The anti-inflammatory properties of olive oil’s non-fat components may also contribute towards its cardio-protective effects, as inflammation and inflammatory responses of the vascular endothelium are known to play an important role in the development of atherosclerosis.
Laboratory studies have also found that 2-(3,4-di-hydroxyphenyl)-ethanol (DHPE), a phenol component of extra-virgin olive oil with potent antioxidant properties, is able to inhibit platelet aggregation (blood clotting) more effectively that other flavonoids (a class of antioxidant polyphenols found in plant foods known to have potentially healthful effects on a multitude of common chronic health problems).
This is important because heart attacks and strokes are caused by blood clots which build up in the arteries of the heart or brain which have been narrowed due to atherosclerotic plaque formation.
The ability to form normal blood clots to physical trauma is of course necessary to prevent hemorrhage (uncontrolled bleeding), however the degree of blood clot inhibition which would occur due to olive oil consumption would not be so severe that it would be dangerous at all.
Olive oil is very high in vitamin E, but other than that, most of its antioxidant properties come from its phenolic components. Phenolic compounds such as flavonoids are widespread in many plant foods and influence the quality, palatability, and stability of foods by acting as flavorants, colorants, and antioxidants.
When consumed, certain phenolic compounds are known to exhibit pharmacological effects on the body, such as anti-carcinogenic (anti-cancer), anti-inflammatory, anti-oxidant, anti-atherogenic effects etc.
These studies suggest that the reduction in LDL oxidation that occurs after consumption of extra-virgin olive oil may be due to its phenolic constituents rather than just its monounsaturated Oleic acid and vitamin E content.
Effects on HDL “good” cholesterol
Animal studies have shown that rats fed olive oil enriched with the non-fatty acid components had greater beneficial effects on HLD “good” cholesterol than did those fed ordinary virgin olive oil, or oil enriched with Oleic acid. This study suggests that substances other than the fatty acid in olive oil may exert beneficial effects on the cardiovascular system.
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