Good cholesterol also has a nasty side that can increase the risk of heart attacks, according to US doctors. "Good", or HDL, cholesterol normally helps to keep arteries clear and is good for heart health.
But the team at the Cleveland Clinic showed it can become abnormal and lead to blocked blood vessels.
They say people should still eat healthily, but that the good cholesterol story is a more complex tale than previously thought.
Low-density lipoprotein (LDL) cholesterol is "bad" because it is deposited in the walls of arteries and causes hard plaques to build up that can cause blockages, resulting in heart attacks and stroke.
High-density lipoprotein (HDL) cholesterol is "good" because the cholesterol is instead shipped to the liver. The evidence shows that having a high ratio of good to bad cholesterol is good for health.
However, researchers at the Cleveland Clinic say trials aimed at boosting levels of HDL have "not been successful" and the role of good cholesterol is clearly more complicated.