When the saturated fatty acids, raisers of the serum cholesterol, are replaced by monounsaturated fatty acids, contained in olive oil, the total cholesterol and low-density cholesterol (LDL cholesterol) concentrations are reduced without reducing the levels of high-density cholesterol (HDL cholesterol).

Consumption of a fat reduced diet with high monounsaturated fatty acids content can reduce total cholesterol and LDL cholesterol (Wahrburg U.et al., 1992).

Also, diets rich in monounsaturated fatty acids are as efficient as diets rich in polyunsaturated fatty acids in decreasing LDL cholesterol and are associated with higher HDL cholesterol concentrations (Mata P., et al., 1992).

Ecologic analysis does not suggest a positive correlation with breast cancer incidence of mortality for olive oil consumption, as they seem to do for consumption of saturated fat. In an article published by Trichopoulou A., et al in 1995, the effect of various types of fat in breast cancer risk from a large case control study undertaken in Greece was studied. Greek women with 42% of energy intake from fat, mostly from olive oil, have substantially lower mortality from breast cancer than the U.S. women whose energy intake from fat is around 35%. This study has generated very similar results with a case-control study in Spain (Martin-Moreno, et al., 1994) suggesting a protective effect of olive oil. The conclusion is evident that olive oil consumption may reduce the risk of breast cancer. Hu F., et al (1997), studied the relation between dietary intake of specific types of fats and the risk of coronary disease. A prospective study of 80,082 women, 34 to 59 years of age and with no known coronary disease, stroke, cancer, hypercholesterolemia, or diabetes was conducted in 1980. During 14 years of follow-up, there were 939 cases documented of nonfatal myocardial infarction or death from coronary heart disease. It was concluded that the replacement of 5 percent of energy from saturated fat with energy from unsaturated fats would reduce risk by 42% and that total fat intake was not significantly related to the risk of coronary disease. These findings suggest that replacing saturated fats with unhydrogenated monounsaturated and polyunsaturated fats is more effective in preventing coronary heart disease in women than reducing overall fat intake.

Biochemical and clinical studies and a number of large European and US population studies have shown beyond doubt that a high-fat diet, rich in saturated fatty acids raises artherogenic low density lipoprotein (LDL) cholesterol and thus is causally related to high incidence of coronary heart disease. In contrast, a diet rich in complex carbohydrates and fiber, and whose fat source is primarily monounsaturated fatty acids, as found in the olive oil-rich Mediterranean style diet, lowers LDL cholesterol and is associated with a low incidence of coronary heart disease. (Keys et al, 1986; Willet, 1990; World Health Organization, 1990)

In another study, Lahoz, et al. (1999), investigated whether changes in dietary fatty acids could modify plasma concentration of glucose, insulin and mean blood pressure. Forty two subjects (18 women and 24 men) were placed in four consecutive five week diet periods. Energy intake from proteins, carbohydrates, and fats was constant during the study and there were only changes in fatty acids composition. No significant changes were found in glucose and insulin plasma concentration. However, a significant effect was detected in mean blood pressure on total population and by gender. They concluded that diets enriched on monounsaturated fatty acids and n-3 polyunsaturated fatty acids significantly decrease the mean blood pressure without modifying glucose and insulin plasma concentrations.

Diabetic patients have a heightened risk of arteriosclerosis. The composition of their LDL is different from that isolated in healthy subjects. In a study run with non-insulin dependent patients, Griffin et al (1996) showed that a diet rich in monounsaturated fatty acids increased patients HDL, and enriching their diet with oleic acid improved their endogenous regulation of cholesterol synthesis. Furthermore, olive oil in the diets of diabetic persons causes a reduction in plasma triglycerides and a decline in very low-density cholesterol (VLDL), while it increases HDL cholesterol, unlike polyunsaturated fatty acids (Wahrburg et al, 1992). One of the most frequent consequences of obesity is dyslipemia, which consists in a rising of VLDL triglycerides, LDL cholesterol and low concentrations of HDL. Olive oil, because of its high oleic acid content, helps correct dyslipemia. On the basis of meta-analysis of several studies, it is clear that compared with high carbohydrate diets, high-monounsaturated fat diets improve lipoprotein profiles as well as the glycemic profile.

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