Triglycerides represent triple esters of glycerol with fatty acids. They are used by many organisms to store energy. In the human organism, they are the main component of adipose tissue.
What are triglycerides?
Triglycerides contain three fatty acids esterified with glycerol in the molecule. Here, the prefix “tri” already indicates the number of fatty acid molecules. The triglycerides are also called lipids and represent fats and fatty oils. However, lipids also include phospholipids, which, in addition to two fatty acids, also have a phosphorylated residue that is also esterified to glycerol. The more double bonds there are in the fatty acids, the lower the melting point. For this reason, fatty oils contain a large number of unsaturated fatty acids (fatty acids with double bonds), which make it difficult to form crystals. To distinguish them from essential oils or mineral oils, they are also called fatty oils. As a rule, esterified fatty acids have 12 to 22 carbon atoms. However, shorter fatty acid molecules can also occur in the triglyceride. Triglycerides containing fatty acids with chain lengths of 4 to 12 carbon atoms are called medium-chain, while triglycerides containing fatty acids with 12 carbon atoms or more are considered long-chain. Furthermore, a distinction is made between simple and mixed triglycerides. The simple triglycerides have three of the same fatty acids, while the mixed representatives contain different fatty acids.
Function, effect, and tasks
Triglycerides are essential for life functions both as a major component of food and in the body as the most important energy store, and are constantly being built up and broken down as part of fat metabolism. In the body, they are built up as an energy reserve in times of food surplus and are mainly deposited in fatty tissue. Considerable amounts of triglycerides can also be stored in the liver. During food intake, the fats and oils contained in the food are broken down by the digestive enzymes of the pancreas to glycerol and the individual fatty acids in order to be absorbed by the small intestine at all. In the intestinal cells, fatty acids and glycerol form triglycerides again. In the blood, so-called lipoproteins ensure the formation of chylomicrons with the fats and oils to make them transportable. Via the bloodstream, they reach all the body’s cells, where they can be metabolized for energy production. Uptake into the body’s cells is mediated by insulin. Insulin thus ensures the uptake of glucose as well as fatty acids and triglycerides into the cells. The carbohydrates and fatty acids that are not needed are converted into body fat, where they are stored as fat in the adipose tissue. In tribal history, this function of triglycerides often ensured the survival of organisms during famines. Today, this function has become less important for most people. Nevertheless, fatty acids, along with carbohydrates, are an important source of energy in normal energy metabolism. Furthermore, fatty acids are often starting materials for important bioactive substances such as cholesterol, fat-soluble vitamins or important hormones (estrogens, testosterone, cortisol, etc.). However, triglycerides can also be converted to phospholipids by replacing a fatty acid with phosphorus-containing compounds. Phospholipids are the major components of cell membranes.
Formation, occurrence, properties, and optimal values
Triglycerides are widely found as dietary fats or oils in most foods. Meat and sausage products in particular are very high in fat. In fish, triglycerides with unsaturated fatty acids are often found as fish oils. Oils are also found in some plants. Nuts and seeds in particular are very rich in oil. In the human body, fats absorbed through food are not stored directly. First, the dietary fats and oils are broken down into fatty acids and glycerol and then re-esterified with each other to re-synthesize the triglycerides. However, fatty acids and glycerol are often also used to produce energy or to synthesize important active ingredients. Furthermore, triglycerides can also be formed from carbohydrates or proteins. In this process, glucose and amino acids are broken down to pyruvate as part of the citric acid cycle. Pyruvate (pyruvic acid) is an intermediate product for the synthesis of many compounds. Among other things, it is also used to build up fatty acids.
Diseases and disorders
Triglycerides have great health significance. Even ingesting too many dietary fats can increase blood lipid levels. Elevated blood lipid levels promote the formation of atherosclerosis, which is responsible for many cardiovascular diseases. In the blood, triglycerides are transported with the help of transport proteins. Pure triglycerides are insoluble in water. The so-called lipoproteins have a mediating effect and bring the fats and oils into solution. In the process, protein-lipid complexes are formed, which have different densities. There are chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL). Chylomicrons transport dietary fats reassembled from food in the intestine into fat cells. There the fats are stored. The very low density lipoproteins (VLDL) are responsible for transporting the endogenous fat produced in the liver into the fat cells. From the fat cells, the triglycerides are shipped by the Low density Lipoproteins (LDL) to all body cells to perform important functions. Finally, high density lipoproteins (HDL) are responsible for transporting cholesterol to the liver where it is broken down. When triglycerides are supplied or synthesized in greater amounts, a lot of LDL is formed to carry cholesterol and triglycerides to the body’s cells. This results in increased deposition of cholesterol and the development of atherosclerosis. With a healthy lifestyle, HDL predominates, bringing cholesterol to the liver for breakdown.
