Particle composed of fat (lipid) and protein that transports fats through the bloodstream. LDLs specifically transport (a lot of) cholesterol from the liver to the tissues of the body. They can leave behind cholesterol deposits (plaques) on artery walls, and contribute to atherosclerosis. Oxidized LDLs have been implicated in the development of cardiovascular diseases.
High density lipoproteins (HDLs) do the opposite. They clean the artery walls and remove extra cholesterol from the body, thus lowering the risk of heart disease.