Cholesterol in the body cannot be broken down in the blood, but must be transported to the liver for metabolism in the form of lipoproteins. Lipoproteins” are so called because they consist of lipids (blood lipids) and proteins (proteins that transport blood lipids). Blood tests can tell how much of this cholesterol is in the body. Low-density lipoprotein (bad cholesterol) Low-density lipoprotein (LDL) comes from two sources: 1. The primary pathway is the metabolic transformation of very low-density lipoprotein (VLDL) by isomerization; 2. The secondary pathway is the direct secretion of LDL into the blood after hepatic synthesis. Because VLDL can cause atherosclerotic plaque formation, make blood vessels lose elasticity and cause narrowing of blood vessels, so LDL is considered as a kind of “bad” cholesterol. If plaque forms in the coronary arteries of the heart, which is often called coronary heart disease, acute myocardial infarction will occur if the plaque ruptures and forms a thrombus; if plaque forms in the brain arteries, which is called cerebral atherosclerosis, brain infarction (stroke) will occur if the plaque ruptures and forms a thrombus; similar lesions will occur in the arteries of other parts of the body, causing local tissue ischemia and necrosis. High-density lipoprotein (good cholesterol) High-density lipoprotein (HDL), synthesized mainly by the liver and small intestine, is an anti-atherosclerotic plasma lipoprotein and is a protective factor against coronary heart disease. It removes LDL cholesterol from the arteries and brings it to the liver like a sanitation worker, and then breaks down the bad molecules of LDL and excretes them from the body through the liver, which is commonly called “vascular scavenger” and is therefore a “good” cholesterol. Therefore, maintaining a certain level of HDL cholesterol can protect the cardiovascular system from myocardial infarction and stroke, but if it is not maintained at a high level, it cannot play a protective role and causes a “garbage siege” effect. Triglycerides are another form of fat that is used by the body to store excess energy in the diet. Studies have found that high triglycerides in the blood are associated with atherosclerosis. Usually overweight and obesity, lack of exercise, smoking, excessive alcohol consumption, and a high-calorie carbohydrate diet (rice, pasta, fats and oils over 60% of total calories) can cause triglycerides to rise. Some people have high triglycerides due to genetics or other diseases. Patients with elevated triglycerides usually have elevated LDL (bad cholesterol) and lower HDL (good cholesterol). Triglycerides are usually elevated in patients with heart disease and diabetes. Lipoprotein a Lipoprotein a is a genetic variant of LDL (bad cholesterol). Elevated lipoprotein a causes lipid deposition in the arterial wall, leading to atherosclerosis. It can be said that lipoprotein a is a relative of LDL, a bad molecule, and is a family accomplice of LDL in the process of causing atherosclerosis.