As many research projects have shown, the composition of olive oil, which as all vegetable oils is made up of triglycerides and minor components, greatly depends, among others, on climatic conditions, soil quality and fruit variety. The fatty acids that make up olive oil triglycerides just like micro components, vary depending on what region the oil is from. Oils therefore around the Mediterranean Basin are not the same and may not have the same effect on the human body as Greek Olive Oil. Research has shown that Greeks despite poor health care had a longer life expectancy (over 80 years) and the world's lowest rates of heart disease and cancer as well as the lowest mortality rate due to cardiovascular illness. Simply said, Greeks seemed to live longer, healthier lives.
The term "Mediterranean diet" is, however, misleading given the large differences between the Mediterranean populations in their dietary habits, e.g. between the Spanish, Italians, French, Egyptians, Israelis, Moroccans and Libyans. Even those that seem close in their dietary habits, such as the Italians, Greeks and Spanish; have large differences in olive oil comsumption, among other characteristics. The mean olive oil consumption of the Italian and Spanish populations is approximately 15-20 gr per person per day as opposed to over double that quantity for a Greek. These differences in dietary habits among the Mediterranean people along with the fact that olive oils appear to have different attributes depending on the region of their origin would suggest that consuming any olive oil as a preventive is not quite enough. Neither is it enough to follow what is called "the Mediterranean Diet". It rather seems that one can not go without the other. That is Greek olive oil with its special qualities and "Mediterranean" style of eating. Although the Chinese believe that food is a kind of medicine, and olive oil might have that interesting quality, it is much more preferable to favor it for its special flavor and the tastefulness it adds to food.
Scientists tried to pinpoint what was that made Greeks so special healthwise. Data was gathered, research and studies carried out and people started to talk about olive oil. Yet, Hippocrates, father of Medicine, had repeatedly referred in his work to the beneficiary attributes of olive oil to health in general, calling it "the great therapeutic". What had been known and applied for centuries in Greece, twentieth century scientists had come to rediscover through their many studies.
Today's scientific research on nutrition has recognized the Greek diet as among the healthiest in the world. Olive oil, rich in monounsaturated fats, is largely responsible for this excellent bill of health. Simply put, olive oil reduces the risk of heart disease by lowering LDL cholesterol (bad cholesterol) which contributes to the buildup of fatty deposits in the arteries. In turn, it leaves HDL (good cholesterol) which works to actually remove any buildup in the arteries that has occurred.
Published studies also link judicious use of olive oil to reducing the effect of a growing list of ailments. For example, Greek women have a 42% lower rate of breast cancer than women in the U.S..
Olive oil is recognized as important in maintaining metabolism and contributes to the development of the brain and bones in children. It is also recommended as a source of vitamin E for older people. A natural anti-oxidant, olive oil slows down the natural aging process. It also slows down acid overproduction in the digestive system thereby diminishing the potential for ulcers and other gastrointestinal problems.
Clearly, olive oil is nothing short of miraculous in its healthful qualities while it contains no more calories than any other oil. A new study by researchers at the University of Oxford, that was published this recently, adds to the growing body of evidence that shows olive oil, a staple of the Mediterranean diet, is as good as fresh fruit and vegetables in keeping colon cancer at bay. Dr Michael Goldacre and a team of researchers at the Institute of Health Sciences compared cancer rates, diets and olive oil consumption in 28 countries including Europe, Britain, the United States, Brazil, Colombia, Canada and China. Countries with a diet high in meat and low in vegetables had the highest rates of the disease and olive oil was associated with a decreased risk. "Olive oil may have a protective effect on the development of colon cancer", Goldacre said in a report in the Journal of Epidemiology and Community Health. Meat, fish and olive oil were the key elements of the diets in terms of the cancer. Meat and fish combined were positively associated with the incidence of cancer but olive oil had a negative effect. The researchers suspect olive oil protects against bowel cancer by influencing the metabolism of the gut. They think it cuts the amount of a substance called deoxycyclic acid and regulates the enzyme diamine oxidase which may be linked to cell division in the bowel. "The olive oil seems to reduce the amount of bile acid and increase the levels of the enzyme thought to beneficially regulate cell turnover in the gut", Goldacre said. Meat has the opposite effect because it tends to increase the amount of bile acid.
Earlier animal studies have shown the benefits of olive oil over safflower and fish oil on pre-cancerous cells and tumour growth. Japanese scientists also claim that virgin olive oil applied to the skin after sunbathing could protect against skin cancer by slowing tumor growth. Colon cancer is the second most common cancer in many Western countries. It is much more prevalent in the industrialized world than in developing nations in Asia and Africa. The main treatment is surgery to remove the cancerous area of the bowel and chemotherapy if the disease has spread.
A study in the March 27, 2000 issue of the journal Archives of Internal Medicine reports that people on high blood pressure medications may be able to reduce the amount of medicine they take if they substitute extra-virgin olive oil for other types of fats in their diet. "The most important finding in this study is that the daily use of olive oil, about 40 grams per day, markedly reduces the dosage of [blood pressure medication] by about 50% in hypertensive patients on a previously stable drug dosage," says L. Aldo Ferrara, MD, associate professor of internal medicine at the Frederico II University of Naples in Naples, Italy, and the study's lead author. Forty grams per day of extra-virgin olive oil amounts to about four tablespoons, Ferrara tells WebMD. That is the amount men in this study consumed, with women consuming about three tablespoons. Each study participant had high blood pressure and was on medicine to control it. Each ate a diet comprised of 17% protein, 57% carbohydrates, 35 grams of fiber, and 26% total fats with 5.8% saturated fats, per day for six months. Participants were assigned to receive the majority of their fats from either extra virgin olive oil or sunflower oil. Then each participant was switched to the other type of oil for an additional six months. During the 12-month study, regular measurements of blood pressure were taken, and when blood pressure fell, the dose of blood pressure medication was reduced. "Daily dosage of [blood pressure medication] was reduced by 48% during the olive oil diet and by 4% during the sunflower oil diet," reports Ferrara. "In particular, blood pressure was controlled without any medication in eight patients during the olive oil diet but none during the sunflower oil diet. Ferrara explains that only extra-virgin olive oil contains antioxidants called "polyphenols," which he and his fellow researchers think may be responsible for the drop in blood pressure seen in this study. Polyphenols are completely absent from sunflower oil, according to Ferrara and colleagues.
Evidence is also growing that olive oil can protect against bowel cancer. Research carried out by doctors at Oxford University has found that olive oil has protective benefits. They found that it reacts with acid in the stomach to prevent the onset of bowel and rectum cancers.
Bowel cancer is the second-most common cancer in the UK and kills nearly 20,000 people every year. However, if it is diagnosed early it is easily treatable. Research carried out in Spain on rats last year also suggested that olive oil could protect against the disease.
But the Oxford researchers have also confirmed that intake of meat and vegetables can affect the risk factors. They studied bowel cancer rates in 28 countries across the world, most of which were in Europe. However, rates of the disease in the UK, the USA, Brazil, Colombia, Canada and China were also examined.
The researchers found that three dietary factors could affect a person's risks of developing the disease. They suggested that people who ate a lot of meat and fish, as opposed to those who ate mostly vegetables and cereals, were at increased risk. They also found that a diet rich in olive oil was associated with a decreased risk. This is because a high meat intake can increase the amount of a bile acid called deoxycyclic acid, which reduced the activity of an enzyme called diamine oxidase (DAO). DAO is thought to regulate the cell turnover in the bowel lining and reduced levels of this enzyme could be responsible for abnormal cell turnover.
But the Oxford researchers found the olive oil seemed to reduce the amount of bile acid and to increase DAO levels, thus protecting against abnormal cell growth and cancer.
Dr Michael Goldacre, one of the authors of the report, said their findings backed up previous studies. "A lot of the major effects we have found are really confirmation of what is by and large already known. What our findings suggest is that countries with high intakes of olive oil have relatively lower incidence rates of colorectal cancer than would be suggested considering other aspects of their diet. We suggest that olive oil does have independent protective affects."
Speaking to BBC News Online he added: "We have suggested that the findings on olive oil need to be tested, confirmed and refuted in other studies before being accepted."
A spokeswoman for the British Nutrition Foundation said more people were using olive oil because of its health benefits. "The main benefit of olive oil has always been in terms of coronary heart disease. Since those benefits have been publicised people have been using olive oil more and more. I think consumption is increasing all the time. The messages of health benefits have certainly been getting out."
A great wealth of information on the many and important health benefits of olive oil is provided by the European Olive Oil Medical Information website. We have included some of this information below for your convenience.
SCIENTIFIC EVIDENCE FOR OLIVE OIL AND ITS EFFECTS ON LIPID METABOLISM
Prof. Dr. med. Gerd Assmann
Dr. troph. Ursel Wahrburg
The Institute of Arteriosclerosis Research at the University of Münster, Germa
Dyslipidaemia as a cardiovascular risk factor
In recent years new clinical recommendations for the assessment and treatment of lipid risk for coronary heart disease (CHD) have been developed by national and international expert and consensus groups as a consequence of a rapidly expanding knowledge basis. Lipid risk factors included in current clinical guidelines are total or low density lipids (LDL) cholesterol, high density lipids (HDL) cholesterol, and plasma triglycerides (12,34,39).
There is no doubt that elevated cholesterol levels due to high levels of LDL cholesterol play a causal role in atherosclerotic heart disease. Extensive observational epidemiological data from both between- and within-population studies relate elevations of total cholesterol or LDL cholesterol to increased CHD incidence. These data are corroborated by genetic and experimental evidence. Furthermore, a large body of interventional epidemiological data, from both primary and secondary prevention trials show a reduction in CHD events with a reduction in total or LDL cholesterol. In general, a 1% reduction in total cholesterol yields a 2-3 % reduction in CHD risk (12,14,24,28).
Numerous epidemiological studies have also established that HDL cholesterol is an independent and powerful predictor of CHD incidence. Until now, information on the effects of increasing HDL cholesterol levels in humans is limited, but suggests favourable effects on CHD risk (12,24,39).
The findings regarding a relation between plasma triglyceride level and CHD incidence are mixed. There is a consistent, strong association in case-control studies. The relation is confirmed in most prospective studies on univariate analysis, but on multivariate analysis of their data it weakens or disappears, in particular when HDL cholesterol, coagulation factors or indicators of abnormal glucose metabolism are taken into account (40).
In the last years evidence has emerged that elevated triglyceride levels confer a high risk for CHD if they occur in conjunction with low HDL cholesterol and elevated LDL cholesterol (so-called lipid triad) or if the LDL/HDL cholesterol ratio is high and triglyceride concentration is elevated. In addition, it has been shown that the conjunction of elevated triglycerides and low HDL cholesterol is often associated with increased insulin resistance, hyperinsulinaemia, higher glucose levels, hypertension, and central obesity. This constellation of risk factors constitutes a syndrome predisposing to atherosclerosis (24,40).
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General cutpoints for dyslipidaemia
As a general rule, there is the finding that one single or isolated lipid value can not be classified as „normal“ or „elevated“. The lipid cutpoints shown in Table 1 are not absolute. They should only be regarded as general advice for risk evaluation and therapy. All other risk factors (Table 2) should be also taken into account when assessing the cardiovascular risk. All therapeutic decisions should generally be based on the patient's overall risk profile. Furthermore, treatment goals for hyperlipidaemia also strongly depend on the global risk (Table 3) (12,24,39).
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Dietary influences on serum lipids and lipoproteins
Decades of research work have clearly demonstrated that diet has a strong influence on serum levels of lipids and lipoproteins. Thus, diet is a cornerstone both in the prevention and treatment of lipid metabolism disorders and CHD.
The action of dietary saturated fatty acids (SFA) as a lipid class to raise total cholesterol levels is well established. The increase in total cholesterol induced by SFA is due mostly to an increase in LDL cholesterol. This increase in LDL cholesterol is accompanied by an elevation of LDL apolipoprotein (apo) B-100, without changes in the ratio between LDL cholesterol and apo B-100. Thus, the increase in LDL cholesterol is due to an increase in the number of LDL particles and not to changes in the cholesterol content of LDL particles. Diets high in fat and SFA also lead to an increase in HDL cholesterol and apo A-I.
This elevation in HDL cholesterol deserves some attention because it is said to antagonise the adverse effects of high LDL concentrations. However, low HDL cholesterol associated with low LDL cholesterol in populations consuming high-carbohydrate, low-fat diets does not increase the coronary risk, whereas populations with high LDL due to high saturated fatty acids (SFA) diets undoubtedly have a high coronary risk in spite of their higher HDL levels. Obviously the magnitude of LDL elevation outweighs the smaller relative increase in HDL cholesterol. Furthermore, the LDL/HDL cholesterol ratio was found to be higher on diets high in total fat and SFA than on low-fat or polyunsaturated fatty acid (PUFA)rich diets in nearly all studies (5,10,20,26,32,33).
Saturated dietary fat usually contains a mixture of SFA of different chain lengths. It has been demonstrated that the different SFA are not equally hypercholesterolaemic. The principal SFA in Western diets is palmitic acid (C16:0), followed by stearic acid (C18:0), myristic acid (C14:0) and lauric acid (C12:0). In a mixed Western diet lauric, myristic and palmitic acids together usually make up about 60-70% of all SFA. These three fatty acids are responsible for the cholesterol-raising effect of saturated fat.
Palmitic acid is the main SFA of animal fat, while myristic acid is abundant in butter fat, palm kernel oil and coconut oil. The latter two also contain very high proportions of lauric acid. It is still a matter of discussion which of the three fatty acids has the highest cholesterol-raising potential, but as a result from several well-controlled studies, the differences among lauric, myristic and palmitic acids appear modest. All three clearly raise LDL cholesterol (8,9,43,48).
The cholesterol-elevating effect of stearic acid, of which the highest content is found in cacoa butter, is much less than that of lauric, myristic and palmitic acids, and more closely approximates the effect of oleic acid. Recent trials, however, have reported a modest fall in HDL cholesterol in response to dietary stearic acid relative to dietary unsaturated fatty acids. Thus, stearic acid and oleic acid are equivalent in their effects on LDL cholesterol but might be somewhat different in their effects on HDL cholesterol concentrations (6,27).
Despite the recent findings about differences in the cholesterol-raising potential of the different SFA, the general recommendation to reduce the amount of SFA consumed in the Western diet is still valid, especially in practice. Most foods contain a mixture of different fatty acids, and, in addition, the cholesterol-elevating SFA are the major fatty acids of a typical Western diet.
In individuals who are not overweight, foods rich in SFA would have to be replaced with other types of food in order to maintain the energy balance in equilibrium. In the past, carbohydrate-rich foods were generally considered to be an ideal candidate for replacing SFA-rich foods. The second alternative as a replacement for saturated fat were polyunsaturated fatty acids (PUFA).
PUFA naturally occur in two major groups with distinct metabolic properties: -3 and -6 fatty acids. These terms indicate the position of the first double bond counting from the methyl end of the fatty acids. The major dietary PUFA is linoleic acid (C18:2, -6) which is predominant in most vegetable oils and in products derived from them. The dietary intake of the other -6-PUFA, -linolenic acid (C18:3,-6) and arachidonic acid (C20:4,-6), represents less than 2% of the total dietary fatty acids.
The -3 fatty acid -linolenic acid (C18:3,-3) is found in very small amounts in many vegetable oils, in higher proportions only in soybean oil, rapeseed oil and linseed oil, whereas the long-chain -3 fatty acids eicosapentaenoic acid (C20:5,-3) and docosahexaenoic acid (C22:6,-3) are contained in fats and oils of marine origin. Marine cold-water fish (herring, mackerel, salmon, tuna) and their products are the major dietary source of these fatty acids. With regard to their effects on lipid metabolism, -3 fatty acids primarily lower serum triglyceride. They have only minor effects on total, LDL and HDL cholesterol (5).
As a cholesterol-lowering alternative to SFA, only -6 PUFA are of importance. The substitution of SFA with linoleic acid leads to a marked fall in total cholesterol. This reduction is mainly due to a decrease in LDL cholesterol which is caused by a reduction in the number of LDL particles. Diets with high amounts of PUFA (>12-15% of energy) and a high P/S ratio (> 2) have been shown to also lower HDL cholesterol (2,11,21,32,35).
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Trans fatty acids
In the majority of naturally occurring unsaturated fatty acids the double bonds are in cis configuration. Trans fatty acids, mainly the trans isomers of oleic acid (elaidic acid (C18:1,-9,trans) and vaccenic acid (C18:1,-7,trans)), are produced during hydrogenation, either in the rumen of cows or in oil-hardening factories. The change from cis to trans configuration of the double bond leads to a straightening of the molecule and to changes in the physical and biochemical properties of the fatty acid. Trans fatty acids have a higher melting point, leading to increased solidity of hydrogenated fats.
The effects of trans fatty acids on serum lipoproteins markedly differ from those of the natural cis isomers. Trans fatty acids have been shown to raise LDL cholesterol concentrations and to decrease HDL cholesterol. Furthermore, they elevate plasma concentrations of lipoprotein (a), an atherogenic lipoprotein that was hitherto thought impervious to dietary changes. However, many people eat no more than a few grams of trans fatty acids per day, and these quantities produce only small effects on serum lipoprotein concentration (1,25,36,38,46,47).
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Olive oil and monounsaturated fatty acids
For many years, monounsaturated fatty acids (MUFA) were not given much attention. More recently, however, a large body of evidence has accumulated showing that MUFA might have some advantages over carbohydrate and PUFA as a substitute for SFA in Western diets.
The major MUFA in the diet is oleic acid (C18:1,-9). Oleic acid is the predominant fatty acid of olive oil (Table 4). Thus, in recent years scientific attention has been focused on the so-called Mediterranean diet and on olive oil as one of its most characteristic components. In the Mediterranean area MUFA usually provide more than 15% of energy (up to 27% in Crete), and they are primarily derived from olive oil. Simultaneously, coronary heart disease incidence, as well as hypercholesterolaemia are by far lower than in other European countries and in the U.S.
Many studies have compared the effects of MUFA and PUFA on plasma lipoproteins under different experimental conditions (2-4,7,11,22,23,29,30,35, 41-46). Well designed and controlled studies are characterised by the following criteria: The dietary intervention trials were conducted with human subjects randomised to a high PUFA-diet and a high MUFA-diet. They consisted of at least two intervention periods which were similar in all respects except for the contents of MUFA and PUFA. Total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides were analysed as end-point data from the dietary intervention periods, and the studies included more than 10 participants on each of the diets to obtain a reasonable accurate estimate of the within-group variance.
The majority of studies conducted under such strict conditions consistently shows that serum total and LDL cholesterol are reduced to a similar extent when MUFA or PUFA were substituted for SFA. Most of these studies used olive oil as the MUFA-rich oil, whereas sunflower or safflower oil was used as PUFA-rich oil. Some experimental diets with a very high PUFA content (> 12% of energy) also showed a decrease in HDL cholesterol. This reduction, however, was not observed after diets with a lower PUFA content (< 12% of energy). The substitution of MUFA for SFA did not lead to any significant changes in HDL cholesterol, even if they were consumed in larger amounts (> 15% of energy).
Two recent meta-analyses confirmed that there is no significant difference in total, LDL and HDL cholesterol between diets relatively high in MUFA versus PUFA when fat intake is primarily derived from common vegetable oils, especially when the fatty acid contents are in a range practicable for a long-term diet. The reductions in total and LDL cholesterol are highly significant, and the LDL/HDL cholesterol ratio is also lowered significantly.
On the basis of these results it no longer seems justifiable to recommend the preferential use of PUFA over MUFA. In addition, there is increasing concern about the long-term safety of high intakes of PUFA: First, there is no country world-wide with a long-term intake of PUFA of 10% of energy or even more that could provide the epidemiological evidence that such high intakes indeed will not cause any harmful health effects. Secondly, PUFA easily undergo peroxidation, yielding free oxygen radicals which could cause serious cellular damage. In some animal experiments very large intakes of PUFA were associated with carcinogenesis. High PUFA intake could induce disbalance among different prostaglandins, leading to coagulation disturbances. It has been further discussed if PUFA are associated with a higher risk of cholelithiasis. Taken together, all these aspects have led to a certain caution regarding the recommendations of PUFA intake.
On the other hand, a high MUFA intake has been proved by the „mass-experiment“ of the Mediterranean countries, where olive oil has been used for centuries. In these countries with low CHD mortality the incidence of cancer, gallstones, and other fat-related diseases is not higher than in other countries. Thus, MUFA can be generally regarded as safe.
Carbohydrates, which have been recommended as a substitute for SFA in cholesterol-lowering diets just as PUFA already for many years, can also be regarded as safe. Low-fat, high-carbohydrate diets significantly lower total and LDL cholesterol concentrations, but they also clearly reduce HDL cholesterol levels (16,17). In addition, those diets may have untoward effects on plasma triglycerides, glucose and insulin. These adverse metabolic effects may be more pronounced in individuals with pre-existing underlying disorders, such as diabetes mellitus. They also depend on the fibre content of the diets. If a carbohydrate-rich diet does not contain only starch and sugar but has a high fibre content, i.e. if the diet contains a lot of whole-grain cereals, vegetables, legumes and fruit, the untoward metabolic effects can be prevented to a large degree.
In summary, the various dietary approaches which can replace SFA in the diet of individuals and populations at high risk for CHD do not differ substantially in terms of their ability to reduce plasma cholesterol and LDL cholesterol which is the major target of a diet for prevention of atherosclerosis. However, their influence on other lipid parameters, non-lipid cardiovascular risk factors and other diseases are not identical. Taking this into account, MUFA seem to have some advantages over both PUFA and carbohydrates (5,13,15,18,19,31,34,37).
From the clinical point of view the best diet in terms of both effectiveness and compliance combines the two dietary approaches of both fat reduction and fat modification. A diet, moderately high in carbohydrates and fibre, not too restricted in total fat, but strictly restricted in SFA, with a moderately high MUFA content seems to be the most feasible approach both to preventing and treating dyslipidaemia.
These scientific findings were of great importance in the formulation of the lipid-lowering diet guidelines of both the European Atherosclerosis Society and the American Heart Association: The total fat intake should be reduced to 30% of the total energy intake, SFA should be reduced below 10% of energy. The intake of PUFA should be not more than 10% of energy (7-10%), whereas the remaining fat proportion should be provided by MUFA (10-15% of energy). The dietary cholesterol content should be below 300 mg/day. Furthermore, the intake of complex carbohydrates and dietary fibre should be increased (12,39).
The traditional Mediterranean diet provides an excellent example how these guidelines could be converted into a tasty and appetising diet. It is characterised by an abundance of plant foods such as bread, pasta, vegetables, salad, legumes, fruit; olive oil as the principal source of fat; low to moderate amounts of dairy products; and also only low to moderate amounts of meat, poultry, fish, and eggs. This diet is low in SFA, rich in carbohydrate and fibre, and, as already discussed, has a high MUFA content. The MUFA are primarily derived from olive oil.
In the most Northern and Western European countries the MUFA intake is also relatively high (15% of energy or more), but the MUFA are mainly taken up with foods simultaneously rich in cholesterol-raising SFA, especially with high-fat animal products. So, if the intake of these SFA-rich foods would be reduced to reach the desirable reduction of the SFA intake from 16-20% at present below 10% of energy as recommended, the MUFA intake as well would fall to 10% of energy or less. Thus, to reach the recommended fat content and composition of the diet, clear changes in the food intake must be made in the Western diets. The intake of vegetable foods has to be greatly increased while the consumption of animal foods, primarily high-fat products such as animal fat, high-fat cheese, fatty meats and sausages, as well as of SFA-rich vegetable fats and oils such as palm and coconut oil, and hydrogenated fat should be clearly decreased.
As a substitute for solid (animal and vegetable) fat, vegetable oils are recommended. Due to its high MUFA content olive oil stands out as a vegetable oil with excellent benefits for human health. The consumption of olive oil increases the MUFA intake without any significant elevation of SFA, and ensures an appropriate intake of the essential PUFA. Thus, olive oil can make a valuable contribution to a healthy lipid-lowering and anti-atherogenic diet.
SCIENTIFIC EVIDENCE FOR OLIVE OIL, THE CARDIOVASCULAR RISK FACTORS AND CORONARY HEART DISEASE
Prof. Dr. med Gerd Assmann
Dr. troph. Ursel Wahrburg
The Institute of Arteriosclerosis Research,
University of Münster, Germany
Atherosclerosis and coronary heart disease (CHD) as its main clinical manifestation have a multifactorial origin. The susceptibility to CHD is determined both by genetic and environmental influences. Among the latter, diet is undoubtedly the central factor in the development of CHD. Dietary factors exert their influence largely through their effects on blood lipids and lipoproteins, but also through their great influence on the other established modifiable risk factors (Table 1), with the exception of cigarette smoking.
Table 1: Risk factors for coronary heart disease (CHD)
Modifiable risk factors Other determinants of risk
Dyslipidaemia Family history of CHD
Cigarette smoking Sex
The dietary factors most directly implicated are dietary fats. Numerous comparisons between populations have shown that there is a strong correlation between the intake of saturated fatty acids (SFA) and CHD morbidity and mortality. A customary diet high in SFA is associated with high levels of CHD. This is the case for the most Western and Northern European countries. On the other hand, in the Mediterranean countries, where people consume their traditional diet in which the majority of fat calories is derived from olive oil, there is a low incidence of CHD. The present paper outlines the effects of monounsaturated fatty acids (MUFA), olive oil, and Mediterranean diet on the different cardiovascular risk factors and on CHD.
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Part A: Olive Oil and Cardiovascular Risk Factors
Part A - 1 Olive Oil and Dyslipidaemia
This topic is covered in Fact Sheet 1.
Part A - 2 Olive Oil and Hypertension
Cross-cultural comparisons and prospective observational studies identify a strong relationship between diet and blood pressure. The studies show that vegetarians in particular have lower blood pressure than non-vegetarians. There is also evidence that the Mediterranean diet might exert a beneficial influence on blood pressure. For instance, significantly lower blood pressures were observed in Italian population samples as compared to Finnish and Scottish groups (41). Until now it could not be clearly determined which of the many nutrient differences compared to usual Western diets were responsible for the blood pressure lowering effect. The partial substitution of vegetables and grain for meat decreases SFAs which are largely derived from animal sources. The intake of MUFA is increased due to the olive oil consumption. In addition, Mediterranean as well as vegetarian diets are characterised by a higher intake of fibre, carbohydrates and micronutrients (eg. potassium, calcium, magnesium), and a lower salt intake.
As a consequence of these observations a large number of different studies have examined the correlation between dietary intake of different types of fat and blood pressure. The majority of cross-sectional studies measuring blood pressure and self-reported diet at the same time, provide no evidence to support the hypothesis that dietary fats affect blood pressure. However, the results must be qualified by taking some methodological weakness into account. In most studies either the measurement of usual diet (eg. 24-hour recall) or blood pressure (eg. only one measurement) was inaccurate or there was an inadequate control of both dietary and non-dietary confounding factors.
Epidemiological prospective studies show conflicting results. For instance, in the Multiple Risk Factor Intervention Trial (MRFIT) (32) with approximately 1200 participants, systolic blood pressure was independently related to SFA intake and dietary cholesterol (48). In contrast, there was no relationship between dietary fat and blood pressure in two large cohort studies: ie: in the Nurses Health Study (57) the 4-year incidence of hypertension was investigated among 58,218 disease-free nurses who completed a dietary questionnaire at baseline. In multivariate analysis controlled for dietary and non-dietary factors, the development of hypertension was not associated with usual intake of total fat, saturated fat, or unsaturated fat. A similar analysis of a cohort of 30,681 US male health professionals confirmed these results (3).
The large sample size of the two latter studies together with their accurate assessment of usual dietary intake and rigorous statistical control for confounding factors provide support for the absence of an association between dietary fat and hypertension or change in blood pressure.
Experimental data of a relationship between dietary fat and blood pressure are also contradictory (for review see 31). In many studies the dietary intervention simultaneously included several measures (eg. exchange of animal fat with vegetable oils plus increase in vegetable consumption). Thus, it is impossible to attribute changes in blood pressure to a single nutrient. In addition, the majority of studies were conducted with normotensive subjects, and their results may not be applied to hypertensive patients.
A well-controlled, randomised cross-over trial compared the effects of a high-fat, high-MUFA diet with a high-fat, high-PUFA diet on blood pressure in healthy adults. No change in blood pressure was found after 4 weeks of treatment (42). There was no evidence of a blood-pressure-lowering effect of either dietary MUFA or PUFA in further studies of normotensive individuals. One study compared a low-fat, carbohydrate-rich diet with a high-fat, olive-oil-rich diet, while holding constant PUFA and SFA (28). Another replaced about 10% of energy with either oleic acid or SFA in otherwise similar diets (30), and two separate studies compared diets rich in MUFA with PUFA, with dietary intake of total fat and SFA held constant (29,34). The effects of MUFA on blood pressure were not tested among hypertensive patients.
In an Italian study the dietary intervention consisted of a change from Mediterranean type diet to a high-fat, high-SFA diet. This dietary modification was obtained by substituting specific items of the habitual diet (olive oil, cereals, vegetables) with foods rich in SFA such as butter, dairy products, cheese, and meat. At the end of the 6-week intervention period systolic and diastolic blood pressure had increased significantly. After return to the customary diet a rapid decrease in blood pressure levels to preintervention values was observed (49). However, in this study there was again a multifactorial dietary intervention and not only an exchange of fatty acids.
A recent Spanish study with 20 healthy volunteers evaluated the effects of two high-fat, MUFA-rich diets (40% fat, 22% MUFA), one with virgin olive oil, the other with high-oleic sunflower oil, as compared with the National Cholesterol Education Program (NCEP) Step 1 diet (30% fat, 12% MUFA) (12). SFA content, dietary cholesterol, fibre, and minerals (sodium, potassium, calcium, magnesium) were kept constant throughout the trial. The MUFA diets which were followed for a 4-week period each led to a significant reduction in systolic (from 120 to 110 mmHg) and diastolic (from 73 to 66 mmHg) blood pressure. Both MUFA oils produced similar changes. Thus, the blood pressure lowering effect was likely to be due to the MUFA, and not to unsaponifiable materials mainly present in olive oil. This well-designed, strictly controlled study gives support that MUFA enrichment of an otherwise unchanged diet has a blood pressure lowering effect. The results indicate that there may be a direct and active influence of MUFA on blood pressure. However, they need confirmation by further studies as well as by investigation of the possible underlying mechanisms.
In summary, the question of the relation between dietary fats and blood pressure has not yet been definitively answered. Evidence suggests that Mediterranean diets with a high consumption of olive oil, cereals, vegetables and fruits have favourable effects on blood pressure. However, it still remains a matter of debate if the protective influence is primarily caused by single nutrients, eg. dietary fatty acids, potassium or dietary fibre, or if it can be attributed to the Mediterranean diet as a whole. There is support for the latter hypothesis suggesting that the combination of various favourable factors - low SFA content, high MUFA content, high carbohydrate, fibre and micronutrient content, low salt intake - leads to lower blood pressure values as compared to typical Western diets. Although the effects of a single nutrient may be small, dietary MUFA content may play a more important role in this protective effect than has been assumed in the past.
Part A - 3: Olive Oil and Diabetes
The prevalence of non-insulin-dependent diabetes mellitus (NIDDM) is very different throughout the world: it is particularly high in Western industrialised countries whereas it is low. Furthermore, the prevalence of NIDDM, and presumably the insulin resistance that invariably accompanies this disorder, has increased dramatically since World War II in all developed countries of the world. The association of increased incidence with economic affluence observed in international comparisons and studies of migrants have illustrated the significance of environmental factors in addition to a genetic disposition. Nutritional factors and the degree of habitual physical activity appear to be important determinants of this form of diabetes. Evidence suggests that the progression from glucose intolerance to diabetes can be prevented by dietary treatment and increased physical activity.
It is known people living in Mediterranean regions are at a particularly low risk developing the most common degenerative diseases of the industrialised populations. Therefore, the question arises whether or not the Mediterranean diet protects from diabetes. Unfortunately, information on the prevalence of diabetes in Mediterranean countries is rare, because there is a lack of properly designed studies. However, although no direct evidence exists which suggests that Mediterranean diet protects against the development of diabetes, there are clear indications from cross-cultural comparisons and studies on vegetarians that some of its most important characteristics - namely, the high intake of complex carbohydrate and dietary fibre and the low intake of SFA - may be beneficial in reducing the risk of diabetes.
The key importance of quantity and quality of dietary fat on the development of diabetes has been underlined in several recent studies. In the San Louis Valley Diabetes Study, fat consumption, adjusted for total energy intake, predicted the risk for NIDDM in individuals with impaired glucose tolerance (27). A high intake of animal fat and cholesterol was found in Japanese-American men with impaired glucose tolerance progressing to NIDDM (51). In the Nurses Health Study, on the other hand, a high, energy-adjusted intake of vegetable fat was associated with a low relative risk of developing diabetes (7). The metabolic mechanisms responsible for this associations have not been identified yet. Assumptions that a high-fat diet might adversely influence insulin-related glucose disposal, could not be confirmed in controlled studies. However, a high-fat diet clearly promotes weight gain and obesity which has been shown to be the dominating risk factor for the development of diabetes in genetically disposed individuals (for review see 19,54). The prevention of obesity is probably the most important measure for reducing the incidence of NIDDM.
Dietary measures are not only important in the prevention of diabetes, but are the cornerstone in the treatment of diabetes. There is no doubt that the basic measure must be a reduction in the intake of SFA. This recommendation is considered of paramount importance by all experts since diabetic patients are exceedingly prone to atherosclerosis. The current guidelines for the treatment of diabetes mellitus favour a diet with a relatively high proportion of carbohydrate-rich foods for most patients (1,11).
Although prospective studies seem to support this approach, controlled dietary treatment studies with diabetic individuals have shown controversial results. Some investigators found that a high-fat, MUFA-enriched diet with a low proportion of energy from SFA, was associated with better glycaemic control and reduced insulin requirements compared with a high carbohydrate diet (12,15,16,17). Furthermore, high-MUFA diets were advantageous because of their effect on lowering of plasma triglyceride and very low density lipoprotein (VLDL) concentrations whilst increasing HDL cholesterol and apo A-I levels (25,38). Although weight-reduction is usually facilitated with high-carbohydrate diets containing fibre-rich foods, high-MUFA diets may have some advantages over diets with a higher energy-density for overweight patients.
The results of these studies indicate that a normoenergetic high-MUFA diet can be consumed by NIDDM patients without negative effects on glucose and lipid metabolism. In addition it may even have some advantages compared to a very-low fat, high-carbohydrate diet, albeit not for all patients. With respect to carbohydrates, it should be emphasised that there are large differences in the effects on glucose metabolism depending on the type of carbohydrate. Patients should be generally advised to choose fibre-rich sources of complex carbohydrates in preference of refined sugars.
In summary, the type and amount of dietary fat influences the risk of developing obesity, insulin resistance and NIDDM. The most important measures for preventing diabetes are weight reduction in obese people, and the restriction of dietary fat, especially saturated fat (SFA), together with increased physical activity. For treatment of NIDDM a high-carbohydrate (fibre-rich) or a high-MUFA diet can be recommended. The choice between the two diets should be based on individual requirements and management goals.
The traditional Mediterranean diet meets all the demands for an adequate diabetes diet. It has a low SFA content and is rich in MUFA due to olive oil . With cereals and vegetables, carbohydrates are mainly taken up as fibre-rich, complex carbohydrates. The absolute fat content can easily be varied - depending on the individual needs - by varying the amount of olive oil in the daily diet.
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Part A - 4: Olive Oil and Obesity
Overnutrition manifested by obesity has emerged as a major health problem in affluent countries. Although obesity is associated with many risk factors for diseases, the mechanisms whereby it enhances disease risk are not fully understood. However, it is generally agreed that overnutrition and obesity only induce disease states when they are combined with an inherent metabolic weakness or defect. In the absence of obesity such defects may well go unnoticed.
One of the most common consequences of obesity is dyslipidaemia, that is, elevations of very low-density lipoprotein (VLDL) triglycerides, low-density lipoprotein (LDL) cholesterol, and low concentrations of high-density (HDL) cholesterol. The two former effects can be explained by overproduction of VLDL, due to obesity, combined with a genetic defect in clearance of VLDL or LDL. The mechanism whereby obesity causes a lowering of HDL cholesterol is unclear (18).
Another disease associated with obesity is cholesterol gallstones. The presence of obesity more than doubles the risk for gallstones. Overnutrition promotes the synthesis of whole-body cholesterol, and the only way for excretion of this excess cholesterol is via the biliary tree. Thus, obesity leads to an increased output of cholesterol in the bile. When this reaction is combined with either a deficiency of bile acids or a propensity to crystal formation, the risk for gallstones is greatly increased (18).
Among patients with NIDDM a high incidence of obesity is well known. It appears that obesity is not the underlying cause of NIDDM, but when combined with a primary defect in insulin metabolism - (a progressive decline in the ability to secrete insulin by beta cells of pancreatic islets or a primary insulin resistance) - NIDDM develops (18).
Approximately 50% of patients with essential hypertension are obese. The mechanisms whereby obesity raises blood pressure are still uncertain. Since many obese patients do not have hypertension, there must be underlying defects in blood pressure control for hypertension to become manifest in obese individuals (18).
Finally, limited data suggest that overnutrition increases the risk for certain types of cancer, namely breast, colon, and prostate cancer. If so, it seemingly is a promoter of cancer development rather than a primary initiator. However, the present data are insufficient to conclude that obesity is definitely a risk factor for human cancer.
The role of obesity as an independent risk factor for cardiovascular morbidity and mortality is also a matter of debate up until now. On the other hand, there is no doubt that obesity strongly increases the cardiovascular risk through its detrimental effects on frequency and severity of the other described risk factors. The obesity-mediated risk is not only determined by the degree of obesity, but also by the body-fat distribution. It has been shown that especially abdominal (visceral) obesity is closely related to cardiovascular risk factors and coronary heart disease (4). Abdominal obesity seems to be associated with a cluster of risk factors, such as dyslipidaemia, NIDDM, and hypertension. This metabolic syndrome is closely linked to visceral fat mass and indicates a very high risk for coronary heart disease.
Obesity is a complex disease with multiple causes. Lifestyle, environment and genetics contribute to its manifestation. Although the pathophysiological mechanisms underlying obesity are not fully understood, it is proven that obesity results from an imbalance in energy intake and energy expenditure. There are many possible causes for this imbalance such as disturbed regulation of food intake, low basal metabolic rate, impaired thermogenesis, and low rates of fat oxidation (39). Numerous studies have shown that the diet of the majority of obese people is not unusually high in calories, but that the fat content is too high. Since dietary fats - in contrast to carbohydrates and protein - are rather stored than oxidised in the postprandial state, a high-fat diet regularly causes weight gain.
In industrialised countries energy-rich foods are easily available, ubiquitous, and, due to their palatability, are given high preference. The calorific foods are believed to be a major cause of obesity. These foods are low in complex carbohydrates and fibre, and rich in fat. The main sources in the diet of most Western countries are foods from animal origin with a high content of „invisible“ fat. Furthermore, an increasing intake of snacks and sweets leads to a further increase in dietary fat as well as in simple carbohydrates. Consumption of vegetable foods rich in complex carbohydrates and fibre is very low.
Epidemiological data convincingly show that there is a strong inverse relationship between carbohydrate intake and relative body weight. Populations with a high carbohydrate intake in general have lower obesity rates as compared to countries with a high fat intake. Epidemiological studies dating from the beginning of the 1960s noted that the prevalence of overweight and obesity in Mediterranean countries was less than that of other industrialised nations. However, since 1960 both lifestyle and dietary habits have changed in most Mediterranean countries. They have moved from a diet based on cereals, vegetables, and olive oil towards a diet rich in animal products. Consequently, the incidence of obesity in Mediterranean countries is increasing (5).
Olive oil is a main component in the traditional Mediterranean diet. As well as other pure fats it has a high energy content and provides 9 kcal (38 kJ) per gram. And, theoretically, an excessive consumption of olive oil could therefore also lead to weight gain and obesity. But, in practice, the amount of olive oil in the usual Mediterranean diet is not large enough to cause obesity. Olive oil is the principle fat source in the diet: intake of animal fat is very low, and the diet contains abundant foods of plant origin. As a consequence, the diet has a high complex carbohydrate and fibre content. Such a diet is usually not hypercaloric, but has an energy content according to the individual energy need.
In summary, obesity is one of the principal public health problems of affluent societies. It is a complex disease with multiple causes. One of the major causes is a high fat content in the habitual diet. In Western countries, consumption of fat, particularly fat derived from animal food, is almost twice as high as the recommended amount, while the carbohydrate content is too low. This is the most important nutritional anomaly of the Western world leading to overnutrition and obesity. A diet rich in complex carbohydrates and fibre, on the other hand, means a protection against the development of obesity. The obvious implications are that obesity could be prevented, or treated through use of a diet rich in grain and vegetables such as the traditional Mediterranean diet.
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Part A - 5: Olive Oil and Thrombogenic Risk Factors
The importance of factors influencing blood clotting and fibrinolysis in preventing coronary events is now well established. There is also evidence that platelet aggregation, plasma fibrinogen concentration and other haemostaseological factors may be influenced by diet. A high intake of saturated fatty acids is believed to increase the risk of arterial thrombosis. The role of unsaturated fatty acids in thrombogenesis still remains controversial (20,33,44).
Dietary supplementation with type n-3 (omega-3) polyunsaturated fatty acids has been shown to modify platelet function, as evidenced by a prolongation of the bleeding time, diminished platelet aggregation and secretion, and attenuated thromboxane production. These diet-related effects on platelets are considered to be beneficial for the prevention of cardiovascular disorders (20,33,44).
Results concerning the effects of n-6 (omega-6) polyunsaturated fatty acids on thrombosis are contradictory. There are some studies which reported a reduced platelet aggregation, while others found an increase (33). It seems that not only the absolute content of linoleic acid is of importance with regard to their thrombotic or antithrombotic effects, but also the content of other fatty acids, eg. the amount of saturated fatty acids and the ratio of n-6 to n-3 fatty acids.
There have been hardly any thorough evaluations of the influence of monounsaturated fatty acids on the coagulation system. The studies conducted so far do not give an indication either of a significant pro- or antithrombotic effect of MUFA. Thus, there is no scientific basis to encourage the consumption of olive oil for reducing the risk of thrombosis (44).
However, the majority of fatty acid and thrombosis studies suggest that both a low-fat or a vegetable-fat diet are preferable to a high-fat diet or a diet high in saturated fatty acids. In this respect, the Mediterranean diet meets the requirements and is a recommendable diet for the prevention of thrombosis.
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Part B: Olive Oil and Coronary Heart Disease
The first hypothesis about a possible relationship between the typical diet of a country and a low incidence of coronary heart disease, including the intermediate role of low serum cholesterol levels, was based on exploratory surveys conducted by Ancel Keys and colleagues in the 1950s in Southern Italy, Spain and Greece. They reported a rarity of cases of hospitalised myocardial infarction which was paralleled by low mean levels of serum cholesterol. These observations were particularly impressive when compared with similar data reported from the United States and Finland, where higher levels of serum cholesterol corresponded to many cases of myocardial infarction. Simultaneously, the Mediterranean populations showed a dietary pattern different from that of North American and Northern European populations.
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Part B - 1 Epidemiological studies
These non-systematic observations became the basis for methodologically more valid approaches which led to the conduction of the Seven Countries Study. This study probably represents until nowadays the major investigation contributing to knowledge about the relationship between the Mediterranean diet and CHD.
The Seven Countries Study was conducted with almost 13,000 men, aged 40 to 59 years, and healthy at entry examination, enrolled in 15 population samples located in seven different countries (Italy, Greece, former Yugoslavia, the Netherlands, Finland, United States, and Japan) (22). Dietary data were collected at different time points. Serum lipids and other risk parameters were measured at baseline and at 5- and 10-year follow-up. The collection of data on mortality and death was continuous from the beginning.
CHD death rates were related to serum cholesterol, blood pressure, smoking habits, and mean age. The death rates, as well as the average diets differed among the cohorts. The major differences in food consumption between the Mediterranean areas and northern Europe and the United States were in the proportions of saturated fat and not necessarily in overall fat consumption. The polyunsaturated fat consumption had relatively minor relevance since the intercohort differences were limited. The monounsaturated fat consumption showed large differences among the cohorts.
15-year CHD death rates were related positively to average percentage of dietary energy from SFA, negatively to dietary energy percentage from MUFA, and were unrelated to dietary energy percentage from PUFA, proteins, carbohydrates, and alcohol. They were also negatively related to the ratio of monounsaturated to saturated fatty acids. All-cause and CHD death rates were low in cohorts with olive oil as the main fat and as the main source of MUFA (Greece, Italy, former Yugoslavia). The intake of SFA, on the other hand, was low, thus resulting in a high MUFA to SFA ratio. A relatively high MUFA intake was also observed in the US cohort, but there it was accompanied by a high SFA intake, a low MUFA/SFA ratio, and, as a consequence, high CHD mortality rates (22).
Among all cohorts from southern Europe, Crete showed the lowest mortality from CHD and all causes. More than other Mediterranean diets, the Cretan diet was, at least in the 1960s, rich in legumes, fruit, and edible fats that were mostly olive oil. The Cretan diet contained much less meat, but supplied moderate amounts of fish and alcohol, mostly in form of red wine (Table 2). The extremely low CHD mortality rates were particularly surprising, since the average serum cholesterol concentrations in the Cretan population were similar to those in the other Mediterranean cohorts.
Table 2: Seven Countries Study: Dietary intake and mortality rates in selected cohorts1
Crete Mediterranean2 Zutphen Netherlands US railroad
Serum Cholesterol (mmol/L) 5.3 5.0 6.0 6.1
Food intake (g/day)4
Bread 380 416 252 97
Vegetables 30 18 2 1
Fruit 464 130 82 233
Meat 35 140 138 273
Fish 18 34 12 3
Edible fat 95 60 79 33
Alcohol 15 43 3 6
1 Adapted from 22,23.
2 n = 9 cohorts.
3 10 years/10,000 men aged 50-69 years.
4 Evaluated in the 1960s.
From the results of the Seven Countries Study, Keys (22) drew the main conclusion that the Mediterranean diet would be ideal for decreasing serum cholesterol concentrations, with most of the cholesterol-lowering effects attributed to both a low intake of saturated fats and to a relatively high intake of monounsaturated fatty acids, specifically oleic acid, which is supplied by olive oil. With regard to the results in Crete, however, it should be emphasised that besides the very important cholesterol-lowering effects due to its favourable fatty acid composition, the Mediterranean diet yields further cardioprotective effects because of the large amounts of cereals, legumes, vegetables, and fruit. These foods contain a variety of nutrients and non-nutrients (antioxidative vitamins and other antioxidants such as polyphenols1) that have been recently shown to play an important role in the prevention of CHD and other chronic diseases.
Since the 1960s, ongoing changes in eating habits have occurred in the Mediterranean region. In Italy, eg. food survey data demonstrate a pronounced increase in the consumption of animal foods (meat, milk, and dairy products), and of edible fats other than olive oil during the past 40 years. Consumption of sugar, fruits, and vegetables has also increased, whereas that of cereals has decreased slightly (14). Comparative changes have been observed in other Mediterranean countries. Increasing evidence suggests that these dietary changes have been accompanied by increases in several cardiovascular risk factors: higher concentrations of serum cholesterol, hypertension, and obesity. In turn, investigators have observed raising rates of CHD and diabetes in various Mediterranean countries (47). These trends confirm the well-established relations between diet and CHD risk and suggest the need to reverse current practices through widespread efforts to preserve and promote traditional diets within the Mediterranean area.
But despite the unfavourable changes in diet, particularly the observed increase in consumption of animal foods, the dietary profile of the Mediterranean countries has still maintained many of its basic features, and recent vital statistics still demonstrate an advantage of eating behaviour, associated with lower CHD mortality rates (Table 3) as compared to Western Europe and the United States (14).
Table 3. CHD mortality rates in Europe and the United States in the 1990s1.
Great Britain and Northern Ireland 288.8
United States 195.7
1 non age-adjusted mortality rates per year per 100.000 persons; data from 1990, 1991 or 1992.
Source: Statistisches Jahrbuch 1995.
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Part B - 2: Interventional studies
Although there is a large body of epidemiological evidence supporting the „diet-heart-hypothesis“, a causal relationship between CHD and the intake of saturated fatty acids or the level of serum cholesterol can only be established by randomised intervention trials. From the 1950s to the 1990s, many intervention trials have been targeted at reducing CHD incidence and mortality. Sometimes, changing a current diet has been used as a single tool for the preventive experiment (such as the Veterans Administration Study (8), the Finnish Mental Hospital Study (52)); sometimes it has been used in combination with other measures (such as the Multiple Risk Factor Intervention Trial (32), the North Karelia Project (37), the WHO European Multifactor Preventive Trial of CHD (56), the Oslo Preventive Trial (21)). In the latter case, it has not been easy to distinguish the role of diet (and of the subsequent cholesterol changes) from that of the other measures.
In most cases, the suggested or implemented changes in dietary habits were oriented towards a reduction in saturated fat, accompanied by an increase in polyunsaturated fat. None of the original Mediterranean diets were particularly rich in polyunsaturated fat. Also, none of the experimental diets were particularly rich in monounsaturated fat, typical of Mediterranean diets due to high consumption of olive oil. Thus, not a single trial including „hard end-points“ has been conducted with the purpose of testing typical Mediterranean diets for the primary prevention of CHD. However, the positive results of saturated fat-reduction obtained in the majority of the trials mentioned above demonstrate the need to reduce the amount of saturated fat in the diet. Furthermore, other intervention studies with „soft end-points“, such as changes in blood lipids, support, at least indirectly, the benefit of a diet resembling that used in the 1950s and 1960s in the Mediterranean region (for review see 10). Besides, there is much evidence from numerous controlled dietary studies that MUFA-rich diets efficiently lower serum total and LDL cholesterol without changing HDL cholesterol levels2.
In summary, in all dietary intervention studies the cholesterol-lowering effects have been shown to be lower than expected. Metabolic “ward” studies have shown the high efficacy of a cholesterol-lowering diet3. However, dietary intake can be maximally controlled and confounding variables, such as changes in body weight and physical activity, are removed. Several requirements must be met before generalisation of the results from metabolic ward studies to free-living populations can be made - the most important is compliance to the dietary regimen. In general, the more intensive the dietary counselling, the greater the compliance. The greater the compliance, the more likely will the results achieved in outpatients approximate the results observed in the metabolic ward setting.
It is well established that a reduction in the cholesterol level will lead to a reduction in morbidity and mortality from CHD4. Most of the studies conducted to test this hypothesis have indeed demonstrated a reduction in the incidence of ischaemic cardiac events, and some have also shown a reduction in mortality from cardiovascular disease (26). In addition, there is also evidence that an intensive lipid-lowering therapy in men with moderate hypercholesterolaemia and no history of myocardial infarction reduces the incidence of myocardial infarction and CHD mortality without adversely affecting the risk of death from noncardiovascular causes (46).
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Part B - 3: Recommendations
All these findings convincingly underline the importance of diet in the prevention of CHD. Statements have been made by different national and international bodies and organisations that recommend preventive diets that are similar to the traditional Mediterranean diet (13,35). The intake of total fat should be reduced to 30% of energy, SFA intake below 10%. The intake of PUFA should not be more than 10% of energy (7-10%), whereas the remaining fat proportion should be provided by MUFA (10-15% of energy). Dietary cholesterol content should be below 300 mg/day. Furthermore, the intake of complex carbohydrates and dietary fibre should be increased. The Mediterranean diet provides an excellent example how these guidelines could be converted into a tasty and appetising diet. It contains an abundance of plant foods such as bread and grain products, vegetables, legumes, and fruit. The amounts of animal products are only low to moderate. Olive oil is the principle source of fat. This diet is low in SFA, rich in carbohydrate and fibre, and has a high MUFA content. The MUFA are primarily derived from olive oil5.
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Part C: Olive Oil and its Role in Secondary Prevention of CHD
In patients with established CHD the European Atherosclerosis Society as well as the National Cholesterol Education Program have recommended more aggressive cholesterol-lowering measures because these individuals are at the highest risk of a CHD event. Several large trials have evaluated the efficacy of cholesterol reduction in secondary prevention of cardiovascular events. Secondary prevention trials are more likely to include subjects who are highly motivated to comply with dietary modifications, thus reducing the problems of nonadherence to diet that is observed in unselected populations or even in high-risk individuals without CHD. The majority of dietary intervention studies achieved at least a 10% reduction in cholesterol levels (2,24,36,55).
With one exception (6), the dietary trials support the role for aggressive dietary therapy in the secondary prevention of CHD. However, despite intensive dietary measures, the reduction in cholesterol concentrations frequently is insufficient. In these cases, an additional drug therapy is necessary to achieve the desired very low cholesterol levels. Impressive examples for the efficacy of intensive lipid-lowering measures are the Scandinavian Simvastatin Survival Study (4S) (45) and the CARE Study (43). They both documented that the significant reduction in total and LDL cholesterol due to a therapy with diet and drugs (HMG-CoA-reductase inhibitor) was associated with a highly significant reduction in non fatal myocardial infarction and CHD mortality in patients after myocardial infarction or CHD.
Until now, only one study has been conducted to investigate the particular effects of a Mediterranean type diet for secondary prevention of CHD (9,40). In the Lyon Diet Heart Study a Mediterranean diet resembling that of Crete in the 1960s was compared to the prudent diet usually recommended in France in 605 patients recovering from myocardial infarction. The experimental group received more bread, more root vegetables and green vegetables, more fish, less meat (beef, lamb and pork to be replaced with poultry), no day without fruit, and butter and cream were replaced with a special, rapeseed oil-based margarine. The oils recommended for salads and food preparation were rapeseed and olive oils exclusively whereas sunflower oil was consumed in the control group. Moderate alcohol consumption in the form of wine was allowed at meals. In terms of nutrients the experimental groups showed a lower intake of SFA, cholesterol, and linoleic acid, but a higher intake of oleic acid, -linolenic acid, and vitamin C as compared to the control group.
Throughout the follow-up period, serum total, LDL, and HDL cholesterol, serum triglycerides, body weight, and blood pressure were similar in both groups. After a mean follow-up period of 27 months, there were 16 cardiac deaths in the control and 3 in the experimental group; 17 non-fatal myocardial infarction in the control and 5 in the experimental group. Overall mortality was 20 in the control and 8 in the experimental group.
The protective effects of the Mediterranean diet which were caused by several factors were largely independent of serum lipids and blood pressure since these risk factors did not differ between the groups. The Mediterranean diet contained a larger proportion of -linolenic acid (18:3n-3) which was provided to a large extent by the rapeseed oil and the rapeseed oil-based margarine. As described above (see „olive oil and thrombogenic risk factors“) n-3 fatty acids have been shown to have favourable effects on bleeding time and platelet aggregation, thus reducing the risk of thrombosis. Furthermore, the intake of oleic acid was higher in the experimental than in the control group due to the intake of olive and rapeseed oils. The control group consumed sunflower oil, and therefore had a higher intake of linoleic acid. Because the cholesterol-lowering effects of both fatty acids were similar in this study, one can suggest that the high oleic acid content has yielded beneficial effects by reducing the oxidation of LDL-cholesterol which is assumed to play an important role in the pathogenesis of atherosclerosis6 . In addition, the increase in natural antioxidants also probably played a protective role by further reducing the susceptibility to lipid peroxidation.
In conclusion, the Lyon Diet Heart Study constitutes the first demonstration that the Cretan Mediterranean diet, even when adapted to a Western population, protects against CHD much more efficiently than a prudent diet, rich in linoleic acid. The specific factors that contribute to the protective effects of this diet need further examination, but the low intake of SFA, the high concentrations of oleic acid, a ratio of 18:3n-3 to 18:2n-6 fatty acids of 1:5, and the high content of natural antioxidants seem to be the most reasonable candidates.
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The Seven Countries Study gave the best scientific proof for the association between a diet low in animal products and saturated fat and low mean population levels of serum cholesterol with low incidence and mortality from CHD. It also documented a negative correlation between the intake of monounsaturated fat and the MUFA to SFA ratio on the one hand and CHD on the other hand. All-cause and CHD death rates were low in cohorts with the MUFA-rich olive oil as the main fat, underlining the favourable role of olive oil. There is a body of indirect evidence from interventional studies that the traditional Mediterranean diet with its abundance in plant foods, preferential and regular intake of olive oil, and low to moderate consumption of animal foods efficiently protects against CHD.
Recent findings indicate that olive oil and the Mediterranean diet yield their benefits not only through their effects on established CHD risk factors such as hyperlipidaemia, hypertension, diabetes, and obesity, but also through directly protective effects, particularly their antioxidative properties. In addition, it has been documented that a Mediterranean diet adapted from the Cretan diet is efficient in the secondary prevention of coronary events and death.
For additional scientific and medical information on the role of diet in general and olive oil in particular, please click on the url located below to visit the European Olive Oil Medical Information site.
|Grades of Olive OilOlive oil is "graded" according to its flavor, color, aroma, as well as its acidity, which is the most important element in determining grade.|
Extra Virgin Olive Oil:
Olives are hand-picked, cleaned with pure water, then crunched and malaxated and finaly cold pressed. Extra virgin olive oil is derived from the first cold pressing of olives without refining. The oil is extracted from the olives by mechanical means (pressure) which do not modify it's basic properties. This results in a completely natural product which maintains the taste plus chemical and biological characteristics of the olive. It is characterized by an acidity level of less than one percent. It is considered the finest and fruitiest olive oil and is therefore also the most expensive. It can range from pale champagne to greenish-gold to bright green in color. In general, the deeper the color, the more intense the olive oil flavor. Nearly 75 percent of Greek olive oil is of this much sought after premium extra virgin grade. This compares to 50 percent of Italy's production and 30 percent of Spain's. The ideal climate of the country contributes most favorably to Greek olive oil's overall superiority. Greek olive oil is richer, with fruitier flavor, intense aroma and distinctive bright green color. Extra virgin olive oil's naturally intense taste is especially complimentary when drizzled over seafood just off the grill, to dress salads, the finishing of sauces and anywhere that richly flavored olive oil will enhance the finished dish. Our "Eliki" olive oil is one of the top brands in this category. We do not sell lower grades of olive oil.
Virgin Olive Oil:
Also derived from the first pressing without refining, virgin olive oil has an acidity level between one and two percent. Although its flavor varies in intensity, virgin olive oil is milder than extra virgin olive oil.
All of the following grades of olive oil involve products that contain refined oils in significant portions and we do not recommend them to our customers due to a number of reasons that have to do with their low nutritional value as well as with their inclusion of chemicals that are harmful to the human body.
Olive oil has an acidity level of no more than 1.5 percent. It is obtained by blending refined oil with 1-15% extra virgin olive oil (the percentage & quality varies). Olive oil from Greece is superior to other olive oils because it contains a portion of good quality extra virgin olive oil. Much lighter in taste and color, olive oil is used for frying or for flavoring certain dishes requiring a more subtle taste than with the richness of extra virgin olive oil. Since olive oil consists primarily of refined oils, which are industrial products of very low quality, we do not recommend it to our customers.
Pure Olive Oil:
Pure olive oil has an acidity level of no more than 1.5 percent. It is a blend of refined olive oil and Pomace oil possibly with a small quantity of extra virgin or virgin olive oil. Since pure olive oil consists primarily of refined oils and Pomace oil, which are industrial products of very low quality, we do not recommend it to our customers.
Refined Olive Oil:
All virgin Olive oil, extracted by cold pressing, which does not conform to the COI (International Oleical Council) standards, is refined to correct the taste and lower the acidity level to 0,3%. This oil is again an industrial product, it has very low nutritional value and lacks all antioxidants and other ingredients that the true 100% extra virgin olive oil has. We do not recommend it to our customers.
Olive Oil Cake Refined:
The oil extracted from olives cake by solvents, has to be refined in order to take off smell and color and lower its acidity to 0,3%. Stay away from this staff. It is bad for you.
Olive Oil Cake (Pomace):
It's a mixture of refined olive oil cake with virgin olive oil, with an acidity limit of 1,5%. Stay away from this staff. It is bad for you.
Spanish Olive Pomace Oil Warning
"Light & Extra Light" Olive Oil:
The olive oil that you see on the supermarket self advertised as "light" or as "Extra Light" olive oil contains the exact same number of calories as regular olive oil and is a mixture of refined olive oils that are derived from the lowest quality olive oils available through chemical processing. These oils are so bad that cannot be consumed by humans without refining. These types of oils also contain significant portions of other lower cost oils such as Canola and Hazelnut oil which have virtually no flavor of their own. They may contain some extra virgin or virgin olive oil (1% maximum). The term "light" or "extra light" refers to the lighter color, fragrance, and flavor obtained by an extremely fine filtration and refining process and not to the amount of calories that the oil contains. We recommend to our customers to stay away from these products because they are industrial products of very low quality.