vidence suggests that a number of nutrients and dietary factors are able to cause beneficial changes to plasma lipoprotein levels. In many cases the effects are superior to pharmaceutical drugs because not only are the physiological effects of the nutrients superior to the medicines, they also possess no side effects which makes them a more healthy long term proposition. Olive oil is one food that has been extensively researched for its beneficial properties on lipoprotein levels. Like red wine, olive oil is a chemical cocktail of plant nutrients, many of which have not been fully characterised. Therefore the mechanisms by which olive oil may have its beneficial effects are not known. The myriad of plant chemicals from the olives are contained within a mainly monounsaturated oil containing primarily oleic acid (OA, C18:1 (n-9)), and some research also suggests these fatty acids may have beneficial effects.
For example, researchers1 have investigated the effects of olive oil on plasma lipoprotein levels in adult subjects with high plasma cholesterol. Subjects consumed a low fat diet for 3 weeks, and then switched to the high olive oil diet for the following 3 weeks. The diets were isocaloric, but the low fat diet was higher in carbohydrates and lower in fat compared to the olive oil diet, which contained 100 g of olive oil. The results showed that following the olive oil diet significant decreases in mean total cholesterol of 9.5 % were observed. In addition, the total apo B plasma concentration, representative of the low density lipoprotein (LDL), lipoprotein(a) and intermediate density lipoprotein (IDL) was reduced by 7.3 %. The LDL fraction of the plasma fell by 12.2 % with addition of olive oil to the diet and triglycerides were reduced by 25.5 %. However, there was no change to high density lipoprotein (HDL), apo A-I or HDL subfractions with olive oil treatment.
These results suggests that, compared to a low fat diet, a diet rich in olive oil can cause beneficial changes to plasma lipoprotein levels. Whether this is due to the monounsaturated fatty acids content of the oil or the phytonutrients contained within the oil is controversial and not fully understood. Some evidence suggests that oleic acid may have beneficial effect on plasma lipoprotein levels. However, there is stronger evidence to suggests that it is the phytonutrients in the oil that are beneficial. Extra virgin olive oil is considered a staple food in the Mediterranean region, and it is thought that this is one components that contributes to the low levels of cardiovascular disease in adherents to the Mediterranean lifestyle. Interestingly, two of the subjects did not respond positively to olive oil and their plasma lipoprotein levels did not improve. The authors concluded that this was die to biochemical individuality, not patient compliance issues.