Blood lipids are fats in the bloodstream, including cholesterol and triglycerides. They are transported in protein complexes and can be measured through a blood lipid profile. The lipid hypothesis links high blood cholesterol levels to heart disease, but some disagree. Lipids have important functions in the body, including forming cell membranes and storing energy.
A lipid can basically be defined as a substance that is insoluble in water but soluble in alcohol or some other type of solvent. Blood lipids are lipids, or fats, in the bloodstream. Some commonly known blood lipids are cholesterol, cholesterol complexes, and triglycerides. These molecules can appear freely in the blood, although they are often packaged and transported in protein complexes.
In general, lipids ingested from food and drink are digested in the small intestine and transported to the liver in large lipid-protein complexes known as chylomicrons. The liver is essentially responsible for ensuring that all tissues receive enough lipids for proper function and for normalizing the concentration of lipids in the blood. In the liver, triglycerides and cholesterol are packaged into complexes of different densities, or lipoproteins, and then released into the bloodstream.
There are three commonly known lipoproteins. Very low-density lipoproteins (VLDL) consist mainly of triglycerides, but will eventually become low-density lipoproteins (LDL). The main ingredient in LDL is cholesterol, and high blood levels of LDL are associated with increased risk of heart disease. High-density lipoproteins (HDL) also consist of cholesterol, but they also contain a large amount of protein and seem to serve as scavengers by cleaning excess cholesterol from the blood. Unlike LDL, a high proportion of HDL in the bloodstream is associated with a protective effect against the development of heart disease.
The lipid hypothesis was first developed in the 1850s to describe the connection between high blood cholesterol levels and heart disease. This hypothesis is accepted as fact by many researchers and clinicians today who claim that years of scientific research have confirmed this association, but a strong minority disagrees with this general view. Opponents of the lipid hypothesis argue that less than half of heart attack patients have high cholesterol levels, and many propose that inflammatory processes are more to blame for heart disease than blood lipid levels.
Due to the generally wide acceptance of the lipid hypothesis, it is often recommended that people older than 20 years of age obtain a blood lipid profile. This profile measures LDL, HDL, and triglycerides, and is a simple blood test that must be performed after a 12-hour fast. Fasting ensures that lipids obtained from the diet have been removed from the bloodstream.
Although blood lipids are often portrayed in a negative light, they have many important functions in a healthy body. They are necessary for the formation of cell membranes, and are the main form of energy storage in the body. Furthermore, lipids are processed in the body to become essential hormones.
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