Triglycerides are one of the types of lipids present in the human body and can be sourced from food or is manufactured within the body. It derives its name from its chemical structure – three long chain fatty acid molecules bind with one glycerol molecule. The most common fatty acids found in triglycerides are stearic acid, palmitic acid and oleic acid. While triglycerides have many useful functions, it is also a central component of obesity and related diseases.
Functions of Triglycerides
- Triglycerides are an important means for the storage of food, not only fats, but also excess carbohydrates and proteins. This can be found in the adipose tissue in the body. When broken down into fatty acids and metabolized by the cell, triglycerides can release large amounts of energy which is more than the energy released in carbohydrate metabolism.
- Triglycerides are also an important source of compounds that can be used to manufacture other lipids like cholesterol. This in turn can be used for the various functions of cholesterol.
- Small amounts of triglycerides are important structural components of cell membranes although it is present in smaller quantities than other lipids like cholesterol and phospholipids.
Triglycerides in Foods
During digestion, triglycerides are split into monoglycerides and glycerol and then resynthesized into triglycerides once it is absorbed. Like other lipids, it is insoluble in water and forms chylomicrons, which is a type of lipoprotein, to travel through the intestinal lacteals and then enter the blood stream. Small amounts of phospholipids and cholesterol are also bound to these chylomicrons and transported from the gut. The source of triglycerides in foods are discussed further under Lipids in Food.
Triglycerides in the Adipose Tissue
In the blood stream, chylomicrons travel to the adipose tissue (“body fat”) and liver. The adipose tissue breaks down the triglycerides into fatty acids and glycerol by the action of the enzyme lipoprotein lipase. Once these components are in the adipose tissue, it is resynthesized into triglycerides and stored in the fat droplet of adipocytes (fat cells). Small amounts of free fatty acids do remain in the adipose tissue and play a role in regulating carbohydrate storage as fat.
When the body needs fatty acids for energy production, the triglycerides are once again hydrolyzed and the fatty acids are carried by the blood protein, albumin, to the target site. Triglycerides stored in the adipose tissue may also be carried to the liver for further processing if necessary.
Triglycerides in the Liver
Triglycerides reach the liver from the adipose tissue as fatty acids and also directly from the gut bound to chylomicrons. The liver is capable of storing triglycerides but its storage capacity is less than adipose tissue. The liver can break down triglycerides into simpler fatty acid molecules which is further processed into compounds like acetyl coenzyme A (acetyl-CoA). These acetyl-CoA molecules condense to form acetoacetic acid which travels to different tissues where it can be used for energy production. Acetyl-CoA is also used for producing other lipids like cholesterol. in the liver. Apart from breaking down triglycerides, the liver also synthesizes triglycerides from excess carbohydrates and proteins – this is the reason that a high intake of calories, even on a low fat diet, will lead to fat deposition.
Triglycerides in the Blood
Triglycerides are transported by lipoproteins. Apart from chylomicrons, large amounts of triglycerides can be found in VLDL (very low density lipoproteins) with decreasing amounts in IDL and LDL. High levels of VLDL in the blood is seen in conditions such as familial hypertriglyceridemia. Like cholesterol, high levels of triglycerides in the blood are associated with coronary heart disease.