Olive oil is unlikely to cause allergic reactions, and as such is used in preparations for lipophilic drug ingredients. It does have demulcent properties, and mild laxative properties, acting as a stool softener. It is also used at room temperature as an ear wax softener. Olive oil is also a potent blocker of intestinal contractions, and can be used to treat excessive Borborygmus.
Oleocanthal from olive oil is a non-selective inhibitor of cyclooxygenase (COX) similar to classical NSAIDs like ibuprofen. It has been suggested that long-term consumption of small quantities of this compound from olive oil may be responsible in part for the low incidence of heart disease associated with a Mediterranean diet.
Another health benefit of olive oil seems to be its property to displace omega-6 fatty acids, while not having any impact on omega-3 fatty acids. This way, olive oil helps to build a more healthy balance between omega-6 fats and omega-3 fats.
Unlike saturated fats, olive oil lowers total cholesterol and LDL levels in the blood. It is also known to lower blood sugar levels and blood pressure.
Olive oil contains the monounsaturated fatty acid oleic acid, antioxidants such as vitamin E and carotenoids, and oleuropein, a chemical that may help prevent the oxidation of LDL particles.
Preliminary research indicates that olive oil could possibly be a chemopreventive agent for peptic ulcer or gastric cancer, but confirmation requires further in vivo study. Olive oil was also found to reduce oxidative damage to DNA and RNA, which may be a factor in preventing cancer.
Unsaturated oils, such as olive oil, have a short shelf life and are prone to becoming rancid from oxidation, which will produce toxic byproducts and a bitter taste. Protection of unsaturated oils from heat and light will delay spoilage.
Olive oil is the main cooking oil in countries surrounding the Mediterranean Sea. Extra virgin olive oil is mostly used as a salad dressing and as an ingredient in salad dressings. It is also used with foods to be eaten cold. If uncompromised by heat, the flavor is stronger. It also can be used for sautéing.
The higher the temperature to which the olive oil is heated, the more one should prefer the use of refined olive oils. When extra virgin olive oil is heated above 350 °F (177 °C), the unrefined particles within the oil are burned. This leads to deteriorated taste. Also, the pronounced taste of extra virgin olive oil is not a taste most people like to associate with their deep fried foods. Refined olive oils are perfectly suited for deep frying foods and should be replaced after several uses.
Choosing a cold-pressed olive oil can be similar to selecting a wine. The flavour of these oils varies considerably and a particular oil may be more suited for a particular dish. Also, people who like lots of tannins in their red wines might prefer more bitter olive oils.
An important issue often not realized in countries that do not produce olive oil is that the freshness makes a big difference. A very fresh oil, as available in an oil producing region, tastes noticeably different from the older oils available elsewhere. In time, oils deteriorate and become stale. One-year old oil may be still pleasant to the taste, but it is surely less fragrant than fresh oil. After the first year, olive oil should be used for cooking, not for foods to be eaten cold, like salads.
The taste of the olive oil is influenced not only by the soil on which the olive trees grow, but also by the moment when the olives have been harvested and ground.
Source and References http://en.wikipedia.org/wiki/Olive_oil