Eurosciences Communications

1. Introduction
2. What are the mechanisms by which olive oil exerts its beneficial effect on health?
3. Scientific Evidence for Olive oil and its effects on lipid metabolism
4. Scientific Evidence for Olive Oil in the Prevention of Cardiovascular Risk Factors and Coronary Heart Disease.
5. Olive oil in secondary prevention of CHD
6. Scientific Basis for Olive Oil, Monounsaturated Fatty Acids, Antioxidants, and LDL Oxidation

At a meeting convened by the European Commission at the Italian National Research Council in Rome, 11 April 1997, European nutrition, cardiology, lipidology and public health specialists gathered to reach a health consensus on olive oil and the Mediterranean diet.

They agreed that there is strong evidence that a Mediterranean-style diet, in which olive oil is the principal source of fat, contributes to the prevention of cardio-vascular risk factors, such as dyslipidaemia, hypertension, diabetes and obesity, and therefore, in the primary and secondary prevention of coronary heart disease.

The major fatty acid of olive oil is oleic acid, a monounsaturated fatty acid (55-83% of total fatty acids). Olive oil contains further saturated fatty acids (range: 8-14%), polyunsaturated fatty acids (range: 4-20%), and other important minor constituents, particularly antioxidants, such as vitamin E and polyphenols.

The beneficial health effects of olive oil are due toboth its high content of monounsaturated fatty acids and its high content of antioxidative substances.

When substituted for serum cholesterol-elevating saturated fatty acids, monounsaturated fatty acids -as contained in olive oil- reduce total and LDL cholesterol concentrations without reducing the levels of HDL cholesterol, thus leading to favourable changes in the serum lipid profile and possibly to changes in the physico-chemical properties of lipoproteins. In this way, olive oil with its high monounsaturated fatty acid content may contribute to the prevention and management of hypercholesterolaemia (LDL), a dominant risk factor for the development of atherosclerosis, and to the prevention of CHD.

Coronary heart disease (CHD) is associated with a number of 'risk factors' eg. smoking, high blood pressure and hyperlipidaemia. Of these risk factors, Ôcholesterol' is particularly important.

Evidence from many sources (genetic, experimental, epidemiological and clinical trial data) consistently shows a strong, independent, relationship between plasma cholesterol and CHD.

Lowering cholesterol levels produces a statistically significant reduction in the incidence of heart attacks. Typically, a 1% reduction in cholesterol produces a 2-3% reduction in CHD risk.

It is now understood that there are two types of cholesterol - low density lipoprotein (LDL) and high density lipoprotein (HDL) - the so-called Ôbad' and Ôgood' cholesterol respectively. High levels of HDL cholesterol reduces CHD risk whereas increased levels of LDL cholesterol increase CHD risk. In addition, high levels of another sort of fat - triglycerides, particularly in the presence of low levels of HDL, and elevated LDL, also confer high risk.

Because of the major contribution of dietary factors to serum lipids and lipoproteins, diet is a cornerstone in the prevention and treatment of CHD. In the Western diet the three saturated fatty acids (SFA), lauric (e.g. palm kernel oil, coconut) myristic (e.g. butter, coconut oil) and palmitic (e.g. animal fat) acids comprise 60-70% of all SFA and are responsible for the cholesterol-raising effect of saturated fat. Stearic acid, found in cocoa butter, is essentially neutral. A common strategy is to reduce SFA in the diet and replace it with polyunsaturated fatty acids (PUFAs), monounsaturated fatty acids (MUFAs) or complex carbohydrates in order to retain a suitable energy balance.

The major dietary PUFA is linoleic acid which is predominant in vegetable oils (e.g. sunflower oil); when substituted for SFA, this markedly reduces total cholesterol. Other PUFAs include, alpha-linolenic acid (e.g. soybean and rapeseed oils) and eicosapentaenoic and docosahexaenoic acid - contained in marine fats and oils (e.g. herring and mackerel) which effectively lower triglycerides, having only minor effects on HDL and LDL cholesterol.

The major MUFA in the diet is oleic acid, which is the predominant fat in olive oil. Olive oil is a major component in the Mediterranean diet, to which it contributes more than 15% of energy. Studies have shown that blood cholesterol levels and the incidence of CHD is much lower in Mediterranean than other countries.

Both MUFAs and PUFAs significantly reduce LDL when substituted for SFA. A high MUFA intake will not alter HDL cholesterol levels significantly. LDL cholesterol examined in subjects fed high-MUFA diets is more resistant to oxidation. (Oxidation causes free radical production which is detrimental to cells). Because of the high consumption of MUFAs among the Mediterranean population over the centuries, MUFAs are generally regarded as being safe.

In accordance with recent European and American dietary guidelines, both fat reduction and the modification of what type of fat you eat are important. Consumption of olive oil increases MUFA intake without significant elevation of SFA and ensures an appropriate intake of the essential PUFA. Therefore it can make a valuable contribution to a healthy diet, reducing the risk of CHD.

4. Scientific Evidence for Olive Oil in the Prevention of Cardiovascular Risk Factors and Coronary Heart Disease.

Olive oil and hypertension

The relationship between dietary fats and blood pressure is not definitively answered. However, evidence suggests that the multiple components of the Mediterranean diet, i.e. low saturated fatty acids (SFAs), high monounsaturated fatty acids (MUFAs), and carbohydrate, fibre, and micronutrient content have favourable blood pressure effects, and therefore that this diet is desirable for health. Dietary MUFA may have a greater protective effect than initially realised.

Olive oil and diabetes

The traditional Mediterranean diet meets all the demands of an adequate diabetes diet. It contains a lot of vegetables and cereals. Carbohydrates are mainly taken up as fibre-rich carbohydrates. It has a low SFA content and is rich in MUFA, mainly from olive oil. The absolute fat content can be varied depending on individual needs. Clearly it is important for diabetic obese patients to lose weight as well as to adopt a healthier diet.

Olive oil and obesity

In Western countries we eat twice as much animal fat as is recommended. This can lead to obesity which is associated with a number of other disease risks. A diet rich in complex carbohydrates and fibre will protect against obesity. A Mediterranean diet will provide optimal energy intake and provides a means with which to treat or prevent obesity.

Olive oil and thrombogenic risk factortrombogenéticos

Most studies suggest that for antithrombotic effects a low fat or a vegetable-fat diet is preferable to a high-fat diet, particularly a high fat diet high in SFAs. The Mediterranean diet meets these requirements and therefore can be recommended for the prevention of thrombosis.

Epidemiological Studies

The Seven Countries Study published in 1970 reported on the dietary intake, blood pressure and cholesterol levels of 13,000 men aged 40-59 years at entry living in Italy, Greece, the former Yugoslavia, the Netherlands, Finland, USA and Japan. CHD deaths were closely related to age, blood pressure and smoking. Saturated fat intake and serum cholesterol levels of the populations were significantly correlated at baseline, 5 and 10 year follow up.

Major differences in the proportions of SFAs and MUFA consumption existed between the Mediterranean countries, northern Europe and the US. Death rates within 15 years were low among the high olive oil consumers where SFA was low (i.e. a high MUFA:SFA ratio): namely, Greece, Italy and Yugoslavia. However, high MUFA intake in the US was apparently counteracted by their high SFA intake (i.e. low MUFA:SFA ratio) and here the CHD mortality was high. Evidence from the Greek island Crete suggested that besides the cholesterol lowering properties of oleic acid (largely from olive oil), other cardioprotective benefits were derived from nutrients and non-nutrients in the Mediterranean diet (e.g. antioxidative vitamins).

Some Mediterranean countries have retained their eating habits over the past 40 years and still show an advantage in terms of lower CHD mortality compared to western Europe and the US.

Agressive treatment of all coronary risk factors, including diet, is an important management approach in secondary prevention of CHD. There is much evidence that diets low in animal products and SFA are associated with low cholesterol levels and reduced CHD rates. Diets high in MUFAs (mainly from oleic acid) also provide this benefit, which is achieved through direct effects on risk factors such as hyperlipidaemia, high blood pressure and so forth, but also via directly protective effects like antioxidant activity.

6. Scientific Basis for Olive Oil, Monounsaturated Fatty Acids, Antioxidants, and LDL Oxidation

Introduction:

Low density lipoprotein (LDL) is the major cholesterol carrying particle in plasma. There is wide agreement that increased levels of LDL are causally related to atherosclerosis and the development of coronary heart disease (CHD). There is increasing evidence that LDL in its Ônative� state is not harmful, but when it becomes altered by a process called oxidation, it becomes a real threat within the arterial wall. The susceptibility of LDL to become oxidised is determined by both internal (endogenous) and external (exogenous) factors. Among the latter, nutritional factors are extremely important, particularly the types of fatty acids and antioxidant vitamins in the diet. This Fact Sheet reviews the mechanisms of LDL oxidation and the role of nutritional factors in its prevention.

LDL oxidation (in atherogenesis)

Half of the cholesterol in the blood is carried in LDL which is a spherical fat-protein particle, consisting of an outer monolayer containing the protein apolipoprotein B (apo B) which surrounds a core containing triglycerides and/or cholesterol esters (non-polar fats). One LDL particle contains about 3600 fatty acids, half of which are polyunsaturated fatty acids (PUFAs). LDL also contains antioxidants, the most important being (alpha) a-tocopherol (vitamin E).

LDL oxidation (peroxidation) is a chain reaction initiated by free radicals, a mainly reactive oxygen species. PUFAs are very susceptible to lipid peroxidation and breakdown to a variety of byproducts which bond to LDL apo B. LDL can be oxidised in vitro by exposing them to smooth muscle and endothelial cells, macrophages (derived from large cells called monocytes), or metal ions (Copper or Iron). LDL oxidation in vivo is poorly understood, and it may be reduced by the presence of antioxidants in plasma such as ascorbic acid (vitamin C). It is therefore likely that LDL oxidation occurs in the artery wall rather than in the blood stream. Vitamin E-enriched LDL is significantly more difficult to oxidise. LDL oxidation is likely to occur when the antioxidant 'defences' are down, especially when a-tocopherol is depleted.

LDL oxidation and atherosclerosis

The essential step in the development of atherosclerosis begins as LDL filter into the arterial wall and become entrapped in the intima where they may undergo oxidative modification. Macrophages (cells formed when monocytes permeate the artery wall from the bloodstream) avidly take up this modified LDL, which contributes to their transformation to foam cells. The accumulation of foam cells in the intima results in the formation of fatty streaks. These do not produce significant obstruction of the artery, but they are gradually converted into fibrous plaques by a mechanism similar to scar formation. These, in turn are gradually transformed into atherosclerotic lesions which underlie most clinical events.

Olive oil and LDL oxidation

There are several potential ways by which dietary fatty acids may influence the oxidation of LDL. The amount and composition of dietary fats affects the amount of LDL in the artery wall. Replacement of dietary saturated fats with monounsaturated fats (MUFAs) or PUFAs lowers LDL levels, thereby decreasing the amount of LDL entering the artery wall and so reducing the amount (and composition) available for oxidation. Because of its high MUFA content, olive oil appears to protect against LDL oxidation (see Section entitled "Effects of dietary fatty acids on LDL oxidation"). Olive oil may afford additional protection by supplying LDL with potent antioxidants, such as vitamin E and phenolic compounds, which will be described later.

Effects of dietary fatty acids on LDL oxidation.

Various studies have investigated the role of MUFA and PUFA in reducing susceptibility to LDL oxidation. Studies in the rabbit model show that oleate-rich (oleic acid is the predominant fatty acid of olive oil) LDL is remarkably resistant to oxidation. Dietary studies in humans support this finding and show that the linoleic acid (the major dietary PUFA which is predominant in vegetable oils) content of LDL is strongly related to the rate and extent of oxidation, with LDL oxidation rate being increased during the PUFA diet compared to the MUFA diet. Further studies have tried to address whether such effects are due to PUFA caused enhancement or a MUFA caused inhibition of LDL oxidation. Dietary supplementation of olive oil suggests that the linoleic acid content of LDL is reduced and that there is less cellular uptake by macrophages and reduced susceptibility of LDL to oxidation.

http://europa.eu.int/olive-oil and http://www.olive-oil.org