Triglyceride

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Image:Fat triglyceride shorthand formula.PNG

Triglyceride (help·info) (also known as triacylglycerol (help·info) 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.

1 Chemical structure
2 Metabolism
3 Role in disease
4 Industrial uses
5 Staining

[edit] Chemical structure

The chemical formula is CH₂COOR-CHCOOR'-CH₂-COOR", where R, R', and R" are long 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 from 5 to 28 carbon atoms, but 17 and 19 are most common. Shorter chain lengths may be found in some substances (butyric acid in butter). 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 significant proportions of branched-chain fatty acids, 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.

In cells, triglyceride (also known as neutral fat) can pass through the cell membrane freely, unlike other molecules, because of its non-polar characteristic which doesn't react with the phospholipid bilayer membrane.

[edit] Metabolism

See also fatty acid metabolism

Triglycerides play an important role in metabolism as energy sources. They contain more than twice as much energy (9 kcal/g) as carbohydrates and proteins. In the intestine, triglycerides are split into glycerol and fatty acids (this process is called lipolysis) (with the help of lipases and bile secretions), which can then move into blood vessels. The triglycerides are rebuilt in the blood from their fragments and become constituents of lipoproteins, which deliver the fatty acids to and from fat cells among other functions. Various tissues can release the free fatty acids and take them up as a source of energy. Fat cells can synthesize and store triglycerides. When the body requires fatty acids as an energy source, the hormone glucagon signals the breakdown of the triglycerides by hormone-sensitive lipase to release free fatty acids. As the brain can not utilize fatty acids as an energy source, the glycerol component of triglycerides can be converted into glucose for brain fuel when it is broken down. Fat cells may also be broken down for that reason, if the brain's needs ever outweigh the body's.

[edit] Role in disease

See also the main article hypertriglyceridemia

In the human body, high levels of triglycerides in the bloodstream have been linked to atherosclerosis, and, by extension, the risk of heart disease and stroke. However, the negative impact of raised levels of triglycerides is lower than that of LDL:HDL ratios. The risk can be partly accounted for by a strong inverse relationship between triglyceride level and HDL-cholesterol level.

Another disease caused by high triglycerides is pancreatitis.

[edit] Guidelines

The American Heart Association has set guidelines for triglyceride levels:

Level mg/dL	Level mmol/L	Interpretation
<150	<1.69	Normal range, lowest risk
150-199	1.70-2.25	Borderline high
200-498	2.25-5.63	High
>500	>5.65	Very high, increased risk

Please note that this information is relevant to triglyceride levels as tested after fasting. Triglyceride levels remain temporarily higher for a period of time after eating.

[edit] Reducing triglyceride levels

Cardiovascular exercise and low-moderate carbohydrate diets containing essential fatty acid are recommended for reducing triglyceride levels. When these fail, fish oils, fibrate drugs, niacin, and some statins are registered for reducing triglyceride levels. Prior alcohol intake can cause elevated levels of triglycerides, and reducing alcohol intake is routinely recommended in patients with high triglyceride levels.

[edit] Industrial induced modifications

Industrial plants processing and using edible oils in large quantities require consistency in the mix of oil molecules, but plant oil availability varies by season. Therefore, oils must be processed first. First, volatile substances are separated out so that unwanted vapours (smells) are not emitted during cooking. This is done by heating the oils and passing steam through the oil. The steam and the heat will remove all the volatile substances. The efficiency of this process is determined by the contact time and the temperature. Contact time can be increased by making a larger factory, but this costs more money. Temperature can be increased, so contact time can be decreased. However, increasing temperature causes unwanted reactions to occur. Temperatures may be pushed up to 190 ºC. At such temperatures, the molecules can undergo transformations that cannot be achieved at normal temperatures; certain branches of the oil molecules change into unnatural positions, yet remain undetected as unnatural by the human body. These unnatural molecules are used as building blocks for cells, and are carcinogens (see trans-isomers).

Large scale processing plants, treating some 100 to 700 tons of oil per day, separate rare fractions of oil molecules that only occur in very small amounts in inexpensive oils. The oils that are typical in cacao, one of the most expensive oils on the industrial market, can also be also be found in small quantities in inexpensive oils such as rapeseed (canola), corn oil, etc. After being separated from the inexpensive oils, these molecules are sold as cacao butter substitutes and can readily be found in candy bars, possibly having undergone heat treatments and hardening treatments.

[edit] Industrial uses

Triglycerides 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.