[Medical Q&A] Does eating too much greasy food the night before having a blood test affect blood lipids?

Author: Jia Mei, Chief Physician, Peking University People's Hospital

Reviewer: Jin Mei, Chief Physician, Beijing Anzhen Hospital, Capital Medical University

Eating too greasy food the night before blood draw can cause an abnormal increase in triglyceride test results.

Blood lipids usually refer to indicators such as cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoproteins, and lipoprotein (a) in plasma. Testing blood lipids can be used to predict the risk of cardiovascular and cerebrovascular diseases.

Although the cholesterol in the body mainly comes from the body's own synthesis, if you eat high-cholesterol foods for a long time, some of the cholesterol in the food will also be absorbed into the blood. When the absorption exceeds the utilization and metabolism, it will lead to increased blood cholesterol.

Triglycerides are exogenous fats that are ingested through the diet. Unlike cholesterol, most of which is synthesized by the body itself. If you eat roast duck or shabu-shabu the night before your blood is drawn, for example, your triglycerides will increase sharply the next day, and sometimes it may be chylous blood (plasma is the color of milk).

Therefore, if you eat particularly greasy food before blood draw, the doctor will tell you to be a vegetarian for 3 days and then have blood draw again, so that the result will be more accurate. If there is a 3-day interval, but the difference between the two triglyceride values ​​is still large, the triglyceride index of the vegetarian diet the night before should be used as the standard. Of course, some patients are born with chylomicronemia, so no matter what they eat or when they have blood drawn, they will have chylomicronemia.

2. What does increased or decreased cholesterol mean?

Total cholesterol refers to the sum of cholesterol contained in all lipoproteins in the blood, including free cholesterol and cholesterol esters. The vast majority of them are cholesterol esters bound to fatty acids, and less than 10% exists in a free state.

Increased cholesterol is related to coronary heart disease, diabetes, hypertension, nephrotic syndrome, hypothyroidism, smoking, drinking, etc.; decreased cholesterol is relatively rare in clinical practice, for example, liver disease, hyperthyroidism, anemia, severe infection, and malnutrition can cause decreased cholesterol.

Low-density lipoprotein combines with cholesterol to form low-density lipoprotein cholesterol. Low-density lipoprotein is synthesized by the liver or converted from very low-density lipoprotein. Increased levels of low-density lipoprotein are associated with atherosclerosis. Lowering low-density lipoprotein cholesterol is beneficial for preventing coronary heart disease and atherosclerosis, but the lower the better. Too low low-density lipoprotein levels can lead to cholesterol transport disorders and further malnutrition. It is enough to control it within an appropriate range.

Elevated LDL cholesterol can cause cerebrovascular and cardiovascular atherosclerosis, leading to cardiovascular and cerebrovascular events. Nephrotic syndrome, diabetes, and pregnancy can also cause elevated LDL cholesterol; malnutrition, chronic anemia, trauma, poor liver function, etc. can cause decreased LDL cholesterol.

High-density lipoprotein cholesterol is a combination of cholesterol and high-density lipoprotein. Because it has the highest density among lipoproteins, it is called high-density lipoprotein cholesterol.

High-density lipoprotein cholesterol is an indicator of anti-atherosclerosis and has a protective effect on blood vessels. High levels of high-density lipoprotein cholesterol reduce the risk of coronary heart disease, and the risk of coronary heart disease is negatively correlated with high-density lipoprotein cholesterol levels. Long-term exercise can increase high-density lipoprotein cholesterol, but some people who smoke or are obese will also have high high-density lipoprotein cholesterol.

Compared with low-density lipoprotein cholesterol, high-density lipoprotein cholesterol is a bad lipoprotein and high-density lipoprotein cholesterol is a good lipoprotein. In the past, it was believed that the higher the HDL cholesterol, the better, and it can protect the cardiovascular system. However, research in recent years has shown that HDL cholesterol also has subcomponents, and is divided into small particles and large particles. If there are more large particles of HDL cholesterol, it will protect against coronary heart disease, while small particles of HDL cholesterol have no protective effect on the cardiovascular system. Therefore, the more large particles of HDL cholesterol, the better, and high small particles of HDL cholesterol cannot reduce the risk of coronary heart disease.