Olive oil is an integral part of the "Mediterranean diet" which is associated with sensible tasty portions and slower, more enjoyable eating. People who eat a "Mediterranean diet" have been shown to have a remarkable variety of health benefits.
Olive oil can quickly satisfy hunger and lead to fewer total calories ingested at mealtime. Studies suggest that olive oil decreases rates of cardiovascular disease and cancer. It is unclear if any single component of olive oil is responsible for these health benefits or if it is a combination of olive oil and a diet high in vegetables, fruit and fish.

Extra virgin olive oil is one of the few oils that can be eaten without chemical processing. (Nearly every other vegetable oil has not been detoxified and refined with steam and solvents).
Fresh pressed olive oil can be eaten immediately and retains the natural flavors, vitamins, minerals, antioxidants, and other healthy products of the ripe olive fruit.

Most doctors advocate lowering total fat and calories in your diet, and substituting butter, margarine and tropical oils with healthy fats like olive oil.