Foods high in saturated fats are thought to increase the risk of heart disease by raising cholesterol levels in the blood. It is thought that trans fats increase the risk of coronary heart disease. Fats normally exist in the cis form in nature. The fatty acids cannot pack closely together so cis fatty acids are liquids at room temperature. Trans-fats are linear and can pack closely together and have higher melting points than the cis-isomer.In the manufacture of margarine some double bonds may be converted from the cis- form to the less healthy trans form. Trans fatty acids raise LDL levels and lower HDL levels. HDLs transport cholesterol out of the blood and LDLs carry cholesterol in the blood and can deposit lipids in artery walls leading to atherosclerosis and restricted blood flow. 