Olive oil and the Mediterranean Diet constitute a healthy benefit source, preventing cardiovascular risk factors. Mainly, this is because olive oil has a high volume of mono-saturated fat acids and antioxidant substances, such as Vitamin E  and polyphenols, favoring bad cholesterol concentrations reduction (LDL) and keeping a good cholesterol concentration (HDL).

1. Scientific evidence of olive oil effects on the lipidic metabolism.

The coronary heart disease (CHD) is related to a series of risk factors such tobacco, high blood pressure and hiperlipidemy. Cholesterol is a particularly important risk factor.
The evidence from different sources (genetic, experimental, results from clinical trials), consistently shows a close and independent relationship between plasmatic cholesterol and coronary heart disease.

The cholesterol levels decrease produce a reduction statistically significant in heart attack cases. Generally, a 1% decrease in cholesterol levels produce 2-3% decrease in coronary heart disease risk.

There are 2 types of cholesterol: low density lipoprotein LDL and high density lipoproteins HDL, which are the so called “bad” and “good” cholesterols, respectively. High levels of HDL cholesterol reduce the risk of coronary heart disease, while high levels of  LDL cholesterol increase the risk of CHD. What is more, high levels of other types of fat (triglycerides), together with low levels of  HDL and increased levels of LDL, also lead to a high risk.

Due to the close relationship between the dietetic factors and the lipids and serum lipoproteins, the diet is the cornerstone in coronary heart disease prevention and treatment. In the Western Diet, the three saturated fat acids (SFA), lauric (almonds oil, coconut oil), myristic (butter, coconut oil), and palmitic (animal fat), comprise 60-70% of the total SFA and are responsible for the increase in saturated fat cholesterol. The stearic acid, present in cocoa butter, is essentially neutral. A common strategy is to reduce the SFA intake and replace them for poly-unsaturated fat acids (PUFA's), mono-unsaturated fat acids (MUFA's) or complex carbohydrates to achieve a proper energetic balance.

The PUFA more common in the diet is the linoleic acid, present mainly in vegetal oils  (sunflower oil). When this substitutes the SFA in the diet, a significant total cholesterol decrease is produced. Other PUFAs are: linoleic acid (soy bean, colza seed oil) and  eicosapentaenoic and docosahexaenoic acids, present in marine fat and oils (herring, mackerel), which effectively reduce the triglyceride levels, causing less impact on the HDL and LDL cholesterols.

The most common MUFA in the diet is the oleic acid because it is the major fat source in olive oil. Olive oil is a major component in the Mediterranean diet, contributing with more than 15% of ENERGY.

Several studies have shown that cholesterol levels in blood and coronary heart disease cases are fewer in the Mediterranean countries than in other countries.

Both MUFA and PUFA reduce considerably LDL  levels when replacing SFA in diet. A high MUFA intake will not alter considerably HDL cholesterol levels. LDL cholesterol level of people on MUFA rich diets is more resistant to oxidation. Oxidation leads to a free radicals production harmful for the cells. Due to the great MUFA intake among the Mediterranean population through centuries, MUFA has been generally considered as safe.

According to recent dietetic European an American standards, fat reduction and fat type modification in the diet are important. The olive oil intake increases the MUFA intake, without a considerable SFA increase and guarantees a proper essential PUFA intake. Therefore, this may provide a valuable contribution for a healthy diet, reducing coronary heart disease risk.

2. Scientific evidence of the olive oil effects on cardiovascular risk and coronary heart disease factors.

Olive Oil and high blood pressure
The link between a fat diet and blood pressure does not have a definite answer. However, evidence suggests that the multiple Mediterranean diet components (low  saturated fat acids concentration (SFA), high mono-unsaturated fat acids, carbohydrates, fiber and micronutrients, carry favorable effects on blood pressure, and therefore, constitute a healthy diet. The MUFA diet may have a higher protective effect than it is believed now.

Olive Oil and Diabetes
The Mediterranean diet comprises all the necessary components for a proper diabetic diet. It contains many vegetables and cereals. Carbohydrates derive mainly from carbohydrates rich in fiber. It presents a low  SFA content and it is rich in MUFA, mainly from olive oil. The absolute fat content may vary according to individual needs. For obese diabetic patients, weight loss and a healthy diet are very important.

Olive Oil and Obesity
In Western countries, double animal fat than recommended is consumed.
This can cause obesity, which is associated with other disease risk factors. A diet rich in complex carbohydrates and fiber will prevent obesity. The Mediterranean diet will provide a proper energy intake to treat and prevent obesity.

Olive oil and Thrombogenic Risk Factors
Most studies suggest that a low fat concentration diet or a vegetal fat diet are preferred, as regards antithrombotic effects, to a high fat diet, specially rich in SFA. The Mediterranean diet fulfils these needs and is advisable to prevent thrombosis.

Epidemiological Studies
The Seven Countries Study published in 1970, provided information about the dietetic intake, blood pressure and cholesterol levels in 13,000 men between 40-49 years old, from Italy, Greece, Yugoslavia, Netherlands, Finland , USA and Japan. Mortality caused by heart disease was closely related to age, seric cholesterol levels and tobacco habit. The study showed a significant correlation between saturated fat intake and seric cholesterol levels of the population at the beginning of the study and after 5 to 10 years of follow-up.

There were great differences in the SFA and MUFA intake among the Mediterranean countries from the North of Europe and the USA. The mortality indexes during 15 years were low in the group with high olive oil intake, where the SFA intake was low (relation MUFA/ high) such as Greece, Italy and Yugoslavia. However, in the USA, the high MUFA intake was apparently counteracted by the high SFA intake (relation MUFA/ low PUFA), resulting in a high mortality caused by heart disease. There is certain evidence in Crete which suggests that apart from the oleic acid properties to reduce cholesterol (mainly from olive oil), there are other  cardio-protector benefits derived from nutrients and non-nutrients in the Mediterranean diet (ex. Antioxidant vitamins).

There are some Mediterranean countries which have kept dietetic habits during the last 40 years and still show certain advances as regards mortality caused by heart disease compared to Western Europe and the USA.

3. Olive oil in the secondary prevention of coronary heart disease (CHD)

The aggressive treatment of all the coronary risk factors, including the diet, is an important method for the CHD secondary prevention. It is evident that a diet deficient in animal products and SFA is associated with low cholesterol levels and CHD reduced levels. The high MUFA diets (oleic acid), also provide this benefit achieved through direct effects on the risk factors such as hiperlipidemy, high blood pressure, and also directly by protector effects such as antioxidant activity.

4. Scientific basis for olive oil, fat acids, mono-saturated, antioxidants and LDL oxidation.

Introduction
The low density lipoprotein (LDL cholesterol) is the main cholesterol transportable particle in plasma. There is a total agreement on that high LDL cholesterol levels are related to arteriosclerosis and the development of coronary heart diseases. There is growing evidence that LDL cholesterol in its " original" estate is not harmful, but when altered through a process called oxidation, it constitutes a real threat to the arterial wall. The LDL-cholesterol oxidation susceptibility is determined by internal factors (endogenous) and external factors (exogenous). Among these latter, the nutritional factors are extremely important, especially because of the fat acid types and antioxidant vitamins present in the diet. This summary revises the LDL-cholesterol oxidation mechanism and the role of the nutritional factors in its prevention.

LDL oxidation (in atherogenesis)
Half of the cholesterol present in the blood is transported as LDL, an spherical fat particle, consisting on an exterior monolayer which contains apolipoprotein B protein (apo B) surrounding a nucleus containing triglycerides and cholesterol estheres (non- polar fat particles). An LDL particle contains around 3,600 fat acids, half of which are fat acids poly-unsaturated (PUFAs). The LDL also contains antioxidants, most of them (alpha) a-Tocopherol (E vitamin)

The LDL oxidation (peroxidation), is a chain reaction initiated by free radicals, the main reactive species of oxygen. The PUFAs  are very susceptible to lipidic peroxidation and to decomposition in a variety of sub-products related to LDL apo B. The LDL can be oxidized in vitro by its contact with the smooth muscle and endothelial cells, macrophages (derived from long cells called monocytes), or  metallic ions (copper or iron). The oxidation in vivo of LDL is not very well known and may be reduced by the presence of antioxidants in plasma such as ascorbic acid (Vitamin C). That is why, it is probable that the LDL oxidation takes place on the artery walls rather than in the blood flow. The enriched LDL vitamin E is harder to oxidize. It is probable that the LDL oxidation takes place when antioxidants defenses are low, especially when a-tocopherol is reduced.

LDL oxidation and Arteriosclerosis
The main step in the  arteriosclerosis development starts when LDL is filtered through the arterial wall and stays trapped inside where it may experiment oxidation modifications. The macrophages (cells formed from monocytes which prevent blood flow  from going through the arterial wall), recover this modified LDL, turning it into foam cells. The accumulation of foam cells in the interior leads to fat lines formation. These do not produce an important obstruction in the artery but eventually, turn into fiber plaques through a mechanism similar to healing. At the same time, these are gradually transformed into arteriosclerosis damages leading to main clinical cases.

Olive oil and LDL oxidation
There are many ways in which fat acids may influence on LDL oxidation. The dietetic fat quantity and composition affect the quantity of LDL on the arterial wall. The replacement of saturated fats for mono-saturated fats (MUFAs) or PUFAs lowers the LDL levels, reducing the quantity of LDL on the arterial wall and the quantity (and composition) available for oxidation. Due to its high  MUFA content, olive oil seems to prevent LDL oxidation (see section titled “ Fat dietetic acids effects on LDL oxidation”). Olive oil provides an additional protection supplying potent antioxidants to LDL such as vitamin E and fenolic compounds which will be described later.

Fat dietetic acids effects on LDL oxidation
Several studies have investigated the role of MUFA and PUFA in the LDL oxidation decrease. Several studies have proved that LDL (oleic acid is the fat acid predominant in olive oil) is considerably resistant to oxidation. Dietetic studies on humans confirm  this finding and show that the linoleic acid content in LDL ( the main dietetic PUFA predominant in vegetal oils), is closely related to the oxidation proportion and quantity, and to a LDL oxidation increased proportion during the PUFA diet compared to MUFA diet. Subsequent studies have tried to figure out if these effects are due to the MUFA increase or due to a PUFA inhibition in LDL oxidation. Olive oil supplements suggest that the linoleic acid content in LDL is reduced and that there is a lower cell absorption by macrophages and a reduction in LDL susceptibility when oxidation takes place.

5. Summary and conclusions

There is vast evidence which states that modifications caused by LDL oxidation play a crucial role in atherogenesis. The LDL oxidation starts by PUFAS peroxidation in the LDL particles. Therefore, the fat acid composition of LDL undoubtedly contributes to oxidation.
The LDL fat acids composition, and therefore, its oxidation susceptibility, is influenced by the diet fat acid. Diets rich in MUFA make LDL more resistant to oxidation modifications, compared to diets rich in PUFA such as linoleic acid.

What is more, the cell membrane fat acid composition depends on the diet and diets rich in MUFA also produce an increase in the MUFA content of the cell membrane and a higher cell oxidation resistance.

The dietetic antioxidants such as vitamin E and C, flavonoids, etc, provide extra protection to oxidation stress. Recent in vitro studies show that not only a-tocopherol, but also olive oil fenolic compounds, inhibit LDL oxidation and reduce the risk of arteriosclerosis. However, additional studies are necessary to explain the mechanisms of action of the fenolic compounds in vivo.

MEDITERRANEAN DIET
Many studies made by the best experts on diets, nutrition and health reveal that the inhabitants of the Mediterranean countries enjoy one of the highest standards of living and life expectancy in the world. The secret of their privileged situation is the Mediterranean Diet, characterized by a high intake of cereal and by-products (bread, pasta, and rice), pulse, vegetables, olive oil and, of course, dry fruits. Although in less quantity, fish, eggs, birds and dairy products are also part of the diet.