Chemical Structure
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 3 to 22 carbon atoms, but 16 and 18 are most common. Shorter chain lengths may be found in some substances (butyric acid in butter). Typically, plants and animals have natural fatty acids that comprise only of even numbers of carbon atoms due to the way they are bio-synthesised from acetyl CoA, however bacteria 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 comprises only of 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.
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 glycogen 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.
Role in Disease
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 a strong inverse relationship between triglyceride level and HDL-cholesterol level.
Other diseases caused by high triglycerides include pancreatitis and depression.
| 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 |
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.
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