Nutritional scientist are interested in olive oil because it is consumed in high amounts by the populations that live around the Mediterranean Sea. These populations tend to have a low incidence of cardiovascular disease. Olive oil contains predominately monounsaturated fatty acids, and is a poor source of the essential fatty acids linoleic acid and alpha linolenic acid, which suggests that the fatty acid content of the oil is not responsible for the health benefits. Like many plants, olives contain a number of phenolic structured compounds that have antioxidant properties, and it is though that it is these compounds that are beneficial to individuals who consume olive oil on a regular basis. However, refined olive oil does not contain these phenols. Therefore only consumption of extra virgin olive oil is beneficial to the cardiovascular system.
For example, research published in the Journal of Nutrition in 20101 demonstrated that consumption of extra virgin olive oil was successful at raising low density lipoprotein (LDL) phenolic levels, but that refined olive oil was not. Further, in the extra virgin olive oil group the phenols within the LDL particles were able to protect them from oxidation. The phenols detected within the LDL particles were hydroxytyrosol monosulfate and homovanillic acid sulfate, which suggests that metabolites of the original phenolic compounds may be responsible for the protective effects. It is known that phenolic compounds undergo extensible phase II metabolism in the enterocytes of the small intestine upon absorption to the gut mucosa, and further metabolism occurs in the liver on first pass metabolism. The major phenols present in refined and extra virgin olive oil are shown in figure 1.
Figure 1. The phenolic content of refined and extra virgin olive oil. Table also shows the fatty acid content and other minor compounds1.
In a similar study2, researchers fed subjects olive oil with low, moderate or high amounts of phenols for 4 days. This short term consumption of olive oil resulted in increase levels of cellular glutathione peroxidase, increase high density lipoprotein (HDL), decrease LDL oxidation and decreased damage to DNA. The phenolic compounds within the plasma increased in a dose dependent manner based on the concentration of phenols consumed in the oil. Olive phenolic compounds may be beneficial to cardiovascular health because they lower blood pressure. For example, researcher who fed healthy European men3 olive oil, demonstrated that systolic blood pressure was reduced by a mean of 3 % in those subjects who did not regularly consume it. Extra virgin olive oil would therefore appear to be beneficial because its phenolic content modulates the cardiovascular system.
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