By now you've probably heard about the cardiovascular benefits of olive oil, which scientists attribute to its monounsaturated fatty acids. "Good oils are not just neutral alternatives to unhealthy saturated and trans fats," says Dr. Arthur Agatston, leading preventive cardiologist and author of The South Beach Diet Supercharged. "They're actually good for you," he adds. However, when you go to the store to buy a bottle of olive oil, you may be bombarded with a variety of types and colors. Below is an explanation of some of the typical varieties you might find — and a reminder about which type to choose.

Olive oils do not differ in the types or amount of fats they contain — all are pressed from tree-ripened olives. The differences lie mainly in the taste, aroma, and concentration of nutrients. Here's the breakdown:

Extra-virgin olive oil: This is the oil we recommend. It comes from the first pressing of the olives, so it's the least refined and therefore has the highest level of antioxidants. It's also the highest quality and most flavorful olive oil, with the lowest acid content.

Virgin olive oil: This comes from the second pressing of the olives and has an acidity of between one and three percent.

Light and extra-light olive oil: This is simply a designation used by companies to market a less flavorful, more acidic type of oil. The term "light" means lighter in color and fragrance, not less fat or calories. These oils are generally between 90 and 95 percent refined olive oil and 5 to 10 percent virgin olive oil. They have had their color, taste, and fragrance removed by the refining process (using a chemical, usually hexane, and steam). This process also destroys the phytochemicals and antioxidants in the oil.

"Adding good fats, like extra-virgin olive oil, to your diet is a smart move," says Dr. Agatston. Other good fats are found in canola oil, fish oil, and the healthy oils in avocados and nuts.