Bad quality olive oil is bad for you while good quality olive oil is very beneficial to your health when used with measure. Bad olive oil is simply a fat that doesn’t taste like much or worse, tastes rancid and does not have any healthy properties.
Fresh extra virgin olive oil is among the healthiest of fats and indeed good for you because it is rich in healthy monounsaturated fats (mainly oleic acid). Top quality olive oil can have high levels of polyphenols (such as oleocanthal) that are known for their antioxidant, anti-inflammatory and antimicrobial characteristics. The presence of some of these compounds can also be tasted as they represent parts of the bitterness and punginess of extra virgin olive oil.