triglyceride n : glyceride occurring naturally in animal and vegetable tissues; it consists of three individual fatty acids bound together in a single large molecule; an important energy source forming much of the fat stored by the body
EtymologyFrom tri- + glyceride.
- (UK) /tɹʌɪˈglɪsəɹʌɪd/
(more properly known as , TAG or triacylglyceride) is glyceride in which the glycerol is esterified with three fatty acids. It is the main constituent of vegetable oil and animal fats.
Triglycerides are formed from a single molecule of glycerol, combined with three fatty acids on each of the OH groups, and make up most of fats digested by humans. A triglyceride is shown in the diagram. Ester bonds form between each fatty acid and the glycerol molecule. This is where the enzyme pancreatic lipase acts, hydrolysing the bond and ‘releasing’ the fatty acid. In triglyceride form, lipids cannot be absorbed by the duodenum. Fatty acids, monoglycerides (one glycerol, one fatty acid) and some diglycerides are absorbed by the duodenum, once the triglycerides have been broken down.
The chemical formula is RCOO-CH2CH(-OOCR')CH2-OOCR", where R, R', and R" are longer alkyl chains. The three fatty acids RCOOH, R'COOH and R"COOH can be all different, all the same, or only two the same.
Chain lengths of the fatty acids in naturally occurring triglycerides can be of varying lengths but 16, 18 and 20 carbons are the most common. Natural fatty acids found in plants and animals are typically composed only of even numbers of carbon atoms due to the way they are bio-synthesised from acetyl CoA. Bacteria, however, possess the ability to synthesise odd- and branched-chain fatty acids. Consequently, ruminant animal fat contains odd numbered fatty acids, such as 15, due to the action of bacteria in the rumen.
Most natural fats contain a complex mixture of individual triglycerides; because of this, they melt over a broad range of temperatures. Cocoa butter is unusual in that it is composed of only a few triglycerides, one of which contains palmitic, oleic and stearic acids in that order. This gives rise to a fairly sharp melting point, causing chocolate to melt in the mouth without feeling greasy.
- See also fatty acid metabolism
Triglycerides cannot pass through cell membranes freely. Special enzymes on the walls of blood vessels called lipoprotein lipases must breakdown triglycerides into fatty acids and glycerol. Fatty acids can then be taken up by cells via the fatty acid transporter (FAT).
Role in disease
- See also the main article hypertriglyceridemia
Another disease caused by high triglycerides is pancreatitis.
GuidelinesThe American Heart Association has set guidelines for triglyceride levels: Please note that this information is relevant to triglyceride levels as tested after fasting 8 to 12 hours. Triglyceride levels remain temporarily higher for a period of time after eating.
When some fatty acids are converted to ketone bodies, overproduction can result in ketoacidosis in diabetics.
Reducing triglyceride levelsModerating the consumption of fats, alcohol and carbohydrates and partaking of aerobic exercise are considered essential to reducing triglyceride levels. Omega-3 fatty acids from fish, flax seed oil or other sources, (up to 3g per day in US, but up to 2g in Europe where it should be associated with Omega-6 with a ideal ω_6/ω_3 ratio near 5, unless under physician care), Omega-6 fatty acids, one or more grams of niacin (mega-dose vitamin B-3) per day and some statins reduce triglyceride levels.
Unlike Japan, it is generally admitted that most populations in western countries are lacking omega-3 nutritional sources. As a result ingesting of excessively high levels of saturated or monounsaturated fatty acids in order to assimilate enough omega-6 fatty acids is common. The ideal ratio ω_6/ω_3 = 5 is almost never met and is most often too high (about 12 in France, up to 80 in the caucasian population of the US and Canada), and unused high levels of saturated or monounsaturated fatty acids accumulate in the body in the form of triglycerides that do not participate in the needed syntheses in the body.
In some cases Fibrates have been used as they can bring down TGs substantially. However they are not used as a first line measure as they can have unpleasant or dangerous side effects. In one case due to an increase in mortality, clofibrate was withdrawn from the North American market.
Alcohol abuse can cause elevated levels of triglycerides.
Industrial usesTriglycerides are also split into their components via transesterification during the manufacture of biodiesel. The fatty acid monoalkyl ester can be used as fuel in diesel engines. The glycerin has many uses, such as in the manufacture of food and in the production of pharmaceuticals. Other examples are the Triglyceride process in the decaffeination of coffee beans.
StainingStaining for fatty acids, triglycerides, lipoproteins, and other lipids is done through the use of lysochromes (fat-soluble dyes). These dyes can allow the qualification of a certain fat of interest by staining the material a specific color. Some examples: Sudan IV, Oil Red O, and Sudan Black B.
triglyceride in Bulgarian: Мазнина
triglyceride in Catalan: Triacilglicèrid
triglyceride in Danish: Triglycerid
triglyceride in German: Triglyceride
triglyceride in Spanish: Triglicérido
triglyceride in Esperanto: Triglicerido
triglyceride in French: Triglycéride
triglyceride in Croatian: Trigliceridi
triglyceride in Indonesian: Trigliserida
triglyceride in Italian: Trigliceride
triglyceride in Hebrew: טריגליצריד
triglyceride in Lithuanian: Trigliceridas
triglyceride in Macedonian: Триглицерид
triglyceride in Dutch: Triglyceride
triglyceride in Japanese: トリアシルグリセロール
triglyceride in Polish: Triacyloglicerole
triglyceride in Portuguese: Triacilglicerol
triglyceride in Russian: Жиры
triglyceride in Finnish: Triglyseridi
triglyceride in Swedish: Triglycerid
triglyceride in Tagalog: Trayglisirayd
triglyceride in Turkish: Trigliserit
triglyceride in Chinese: 三酸甘油脂