Nutrition Article I

Olive oil and cardiovascular disease: Cholesterol and artherosclerosis

The beginnings of the current interest in the Mediterranean diet, characterised by a low content of saturated fatty acids (animal fats and palm and coconut oil) and by monounsaturated-rich olive oil as its main source of fat, can be traced back to Ancel Keys, of the University of Minnesota. In 1952, Keys was struck by the low incidence of coronary heart disease in Naples (Keys et al, 1954), which led him to believe there was a link between dietary fat consumption, elevated cholesterol levels and the risk of mortality from cardiovascular disease.

The first studies conducted in the 1950s and 1960s measured total cholesterol levels as opposed to the levels of cholesterol transported by low-density (LDL) and high-density (HDL) lipoproteins. This led to the conclusion that the replacement of saturated fatty acids by monounsaturates did not affect serum cholesterol levels and that the substitution of polyunsaturates for saturated fatty acids lowered cholesterol levels (Keys, Grande Covián and Anderson, 1965). However, later advances in the determination of blood lipid profile prompted re-assessment of these results.

This observation culminated in the body of research known as the Seven Countries Study (Keys, 1970), which provided major epidemiological evidence of the effects of fats and fatty acids on serum cholesterol levels. On comparing the diet of population groups in countries such as Greece, Italy, Yugoslavia, Finland, Japan, the Netherlands and the United States, this was the first international prospective study of its kind and a scientific cornerstone on the health advantages of the Mediterranean diet. It was the first reference of the beneficial effects of olive oil and demonstrated that the incidence of cardiovascular disease amongst middle-aged men on Crete was lower than expected and directly proportional to their total cholesterol levels.

Primarily owing to their high consumption of olive oil, their traditional diet supplied them with a high content of total fat (40% of total daily energy) but a low content of saturated fatty acids. This low incidence of vascular disease was linked to the potentially beneficial effects of monounsaturated-rich diets on lipoprotein profile, which led to the belief that the kind of fat is what matters, not the quantity. Subsequent studies comparing different population groups have provided further confirmation of the benefits of the olive-oil-rich Mediterranean diet (Kouris-Blazos et al., 1999; Kafatos et al., 1999).

In 1985, Mattson and Grundy, of the University of Dallas, reported that olive oil lowered serum cholesterol without lowering HDL-cholesterol, which plays a protective, anti-atherogenic role by encouraging the elimination of LDL-cholesterol (Gordon et al, 1977).

In 1986, Sirtori et al. demonstrated that besides its effect on cholesterol and atherosclerosis, olive oil also has a preventive effect on thrombosis and platelet aggregation. High intakes of olive oil are not harmful; they lower serum LDL-cholesterol levels but do not lower HDL levels, which they may even raise.