Difference between revisions of "Fat" - New World Encyclopedia
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This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the [[diet]] of most [[heterotroph]]s (including humans). | This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the [[diet]] of most [[heterotroph]]s (including humans). | ||
| − | == | + | ==The chemical structure of fats== |
[[Image:Trimyristin.png|thumb|right|150px|The chemical structure of [[trimyristin]], a triglyceride.]] | [[Image:Trimyristin.png|thumb|right|150px|The chemical structure of [[trimyristin]], a triglyceride.]] | ||
| − | The basic components of triacylglycerols are [[fatty acid]]s, a class of compounds that consist of a long hydrocarbon chain and a terminal caroxylate group. In a fat molecule, three fatty acid chains are bonded to a glycerol backbone. Chemically speaking, fat is considered a [[ester|triester]] of glycerol, as it is a molecule formed from | + | The basic components of triacylglycerols are [[fatty acid]]s, a class of compounds that consist of a long hydrocarbon chain and a terminal caroxylate group. In a fat molecule, three fatty acid chains are bonded to a glycerol backbone. Chemically speaking, fat is considered a [[ester|triester]] of glycerol, as it is a molecule formed from a [[condensation reaction]] between an organic acid and an alcohol. |
Fatty acids vary in two important characteristics: (1) chain length and (2) degree of unsaturation. The chemical properties of triacylgycerols are thus determined by their particular fatty acid components. | Fatty acids vary in two important characteristics: (1) chain length and (2) degree of unsaturation. The chemical properties of triacylgycerols are thus determined by their particular fatty acid components. | ||
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Natural sources of fatty acids are rich in the ''cis'' isomer. In contrast, [[trans fat]]s are popular with manufacturers of [[Food preservation|processed foods]] because they are less vulnerable to [[rancidity]] and more solid at room [[temperature]] than ''cis'' fats. However, trans fats reduce the fluidity (and functionality) of [[Cell (biology)|cell]] [[membrane]]s. Trans-fats have been associated with many health problems, but their biochemistry is poorly understood. | Natural sources of fatty acids are rich in the ''cis'' isomer. In contrast, [[trans fat]]s are popular with manufacturers of [[Food preservation|processed foods]] because they are less vulnerable to [[rancidity]] and more solid at room [[temperature]] than ''cis'' fats. However, trans fats reduce the fluidity (and functionality) of [[Cell (biology)|cell]] [[membrane]]s. Trans-fats have been associated with many health problems, but their biochemistry is poorly understood. | ||
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| + | ==Types of fats and their chemical properties== | ||
| + | '''Saturated fat''' is [[fat]] that consists of [[triglycerides]] containing only [[Saturation (chemistry)|saturated]] [[fatty acids]]. Saturated fatty acids have no [[double bond]]s between the [[carbon]] [[atom]]s of the fatty acid chain (hence, they are fully saturated with [[hydrogen]] atoms). There are several kinds of naturally occurring saturated fatty acids, with their only difference being the number of carbon atoms - from 1 to 24. Some common examples of saturated fatty acids are [[butyric acid]] with 4 carbon atoms (contained in [[butter]]), [[lauric acid]] with 12 carbon atoms (contained in [[Breast milk]], [[coconut oil]], [[palm oil]], and [[cocoa butter]]), [[myristic acid]] with 14 carbon atoms (contained in cow [[milk]] and dairy products), [[palmitic acid]] with 16 carbon atoms (contained in [[meat]]) and [[stearic acid]] with 18 carbon atoms (also contained in [[meat]]). | ||
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| + | Fat that occurs naturally in [[living matter]] such as [[animal|animals]] and [[plants]] is used as [[food]] for human [[ingestion|consumption]] and contains a varying proportion of saturated and [[unsaturated fat]]. Foods that contain a high proportion of saturated fat are [[butter]], [[ghee]], [[suet]], [[tallow]], [[lard]], [[coconut oil]], [[cottonseed oil]] and [[palm kernel oil]], [[dairy product]]s (especially [[cream (food)|cream]] and [[cheese]]), [[meat]] as well as some prepared foods. | ||
| + | |||
| + | In nutrition, '''polyunsaturated fats''' are a [[fatty acid]] in which more than one [[double bond]] exists within the representative [[molecule]]. That is, the molecule has two or more points on its structure capable of supporting [[hydrogen]] [[atoms]] not currently part of the structure. By contrast, [[polysaturated]] [[fatty acids]] can assume a ''[[cis]]'' or ''[[trans]]'' | ||
| + | [[Conformational isomerism|conformation]] depending on the geometry of the double bond. | ||
| + | |||
| + | The lack of the extra hydrogen atoms on the molecule's surface typically reduces the strength of the compound's [[Intermolecular force|intermolecular forces]], thus causing the [[melting point]] of the compound to be significantly lower. This property can be observed by comparing predominately [[unsaturated]] [[vegetable]] [[oil]]s, which remain [[liquid]] even at relatively low temperatures, to much more [[saturated fat|saturated]] fats such as [[butter]] or [[lard]] which are mainly [[solid]] at [[room temperature]]. [[Trans fats]] are more similar to saturated fat than are [[cis]] fats in many respects, including the fact that they solidify at a lower temperature. | ||
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| + | In nutrition, monounsaturated fats are fatty acids with one double-bonded carbon in the molecule, with all of the others single-bonded carbons, in contrast to polyunsaturated fatty acids which have more than one double bond. | ||
| + | Fatty acids are long-chained molecules having a methyl group at one end and a carboxylic acid group at the other end. Fatty acid fluidity increases with increasing number of double bonds. Therefore, monounsaturated fatty acids have a solidification temperature that is higher than that of polyunsaturated fatty acids, but still below that of saturated fatty acids. | ||
| + | The most common monounsaturated fatty acids are palmitoleic acid (16:1 n−7) and oleic acid (18:1 n−9). Palmitoleic acid has 16 carbon atoms with the first double bond occurring 7 carbon atoms away from the methyl group. Oleic acid has 18 carbon atoms with the first double bond occurring 9 carbon atoms away from the methyl group. The illustration below shows a molecule of oleic acid. | ||
| + | Monounsaturated fats are found in natural foods like nuts and avocados, and are the main component of olive oil (oleic acid). They can also be found in grapeseed oil, ground nut oil, sesame oil and corn oil. Canola oil is 57%−60% monounsaturated fat and olive oil is about 75% monounsaturated fat. | ||
Saturated and unsaturated fats differ in their energy content and melting point. Since an unsaturated fat contains fewer carbon-hydrogen bonds than a saturated fat with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms. Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature. However, the rigid double bond in an unsaturated fat fundamentally changes the chemistry of the fat. The ''cis''-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently like with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. Trans-fats, however, may still stack like saturated fats, but are not as susceptible to metabolization. | Saturated and unsaturated fats differ in their energy content and melting point. Since an unsaturated fat contains fewer carbon-hydrogen bonds than a saturated fat with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms. Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature. However, the rigid double bond in an unsaturated fat fundamentally changes the chemistry of the fat. The ''cis''-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently like with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. Trans-fats, however, may still stack like saturated fats, but are not as susceptible to metabolization. | ||
Revision as of 22:08, 1 October 2006
| Types of Fats in Food |
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| See Also |
- For other uses, see Fat (disambiguation).
Fats (also known as neutral fats, triglycerides, or triacylglycerides) are uncharged esters of glycerol, a three-carbon alcohol. They belong to a larger class of biomolecules called lipids, which are water-insoluble but highly soluble in organic solvents.
This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the diet of most heterotrophs (including humans).
The chemical structure of fats
The basic components of triacylglycerols are fatty acids, a class of compounds that consist of a long hydrocarbon chain and a terminal caroxylate group. In a fat molecule, three fatty acid chains are bonded to a glycerol backbone. Chemically speaking, fat is considered a triester of glycerol, as it is a molecule formed from a condensation reaction between an organic acid and an alcohol.
Fatty acids vary in two important characteristics: (1) chain length and (2) degree of unsaturation. The chemical properties of triacylgycerols are thus determined by their particular fatty acid components.
Chain length
Fatty acids in naturally occurring triglycerides typically range from 14 to 24 carbon atoms, with 16- and 18-carbon lengths being the most common. Fatty acids found in plants and animals are typically composed of an even number of carbon atoms, due to the process of biosynthesis in these organisms. 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.
Fatty acids with long chains are more susceptible to intermolecular forces of attraction (in this case, van der Waals forces), raising their melting point. Long chains also yield more energy per molecule when metabolized. The lower melting point of unsaturated fatty acids, in contrast, enhances their fluidity.
Degree of unsaturation
Fatty acids may also differ in the number of hydrogen atoms that branch off of the chain of carbon atoms. Each carbon atom is typically bonded to two hydrogen atoms. When a fatty acid has this typical arrangement, it is referred to as a saturated fatty acid, because the carbon atoms are "saturated" with hydrogen; that is, they are bonded to the maximum number of hydrogen atoms.
In unsaturated fatty aids, a carbon atom may instead bond to one hydrogen atom and form a double bond to a neighboring carbon atom. These double bonds may occur either in a cis or trans isomer, depending on the geometry of the double bond. In the cis conformation, the hydrogens are on the same side of the double bond, whereas in the trans conformation, they are on the opposite side.
Natural sources of fatty acids are rich in the cis isomer. In contrast, trans fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and more solid at room temperature than cis fats. However, trans fats reduce the fluidity (and functionality) of cell membranes. Trans-fats have been associated with many health problems, but their biochemistry is poorly understood.
Types of fats and their chemical properties
Saturated fat is fat that consists of triglycerides containing only saturated fatty acids. Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain (hence, they are fully saturated with hydrogen atoms). There are several kinds of naturally occurring saturated fatty acids, with their only difference being the number of carbon atoms - from 1 to 24. Some common examples of saturated fatty acids are butyric acid with 4 carbon atoms (contained in butter), lauric acid with 12 carbon atoms (contained in Breast milk, coconut oil, palm oil, and cocoa butter), myristic acid with 14 carbon atoms (contained in cow milk and dairy products), palmitic acid with 16 carbon atoms (contained in meat) and stearic acid with 18 carbon atoms (also contained in meat).
Fat that occurs naturally in living matter such as animals and plants is used as food for human consumption and contains a varying proportion of saturated and unsaturated fat. Foods that contain a high proportion of saturated fat are butter, ghee, suet, tallow, lard, coconut oil, cottonseed oil and palm kernel oil, dairy products (especially cream and cheese), meat as well as some prepared foods.
In nutrition, polyunsaturated fats are a fatty acid in which more than one double bond exists within the representative molecule. That is, the molecule has two or more points on its structure capable of supporting hydrogen atoms not currently part of the structure. By contrast, polysaturated fatty acids can assume a cis or trans conformation depending on the geometry of the double bond.
The lack of the extra hydrogen atoms on the molecule's surface typically reduces the strength of the compound's intermolecular forces, thus causing the melting point of the compound to be significantly lower. This property can be observed by comparing predominately unsaturated vegetable oils, which remain liquid even at relatively low temperatures, to much more saturated fats such as butter or lard which are mainly solid at room temperature. Trans fats are more similar to saturated fat than are cis fats in many respects, including the fact that they solidify at a lower temperature.
In nutrition, monounsaturated fats are fatty acids with one double-bonded carbon in the molecule, with all of the others single-bonded carbons, in contrast to polyunsaturated fatty acids which have more than one double bond. Fatty acids are long-chained molecules having a methyl group at one end and a carboxylic acid group at the other end. Fatty acid fluidity increases with increasing number of double bonds. Therefore, monounsaturated fatty acids have a solidification temperature that is higher than that of polyunsaturated fatty acids, but still below that of saturated fatty acids. The most common monounsaturated fatty acids are palmitoleic acid (16:1 n−7) and oleic acid (18:1 n−9). Palmitoleic acid has 16 carbon atoms with the first double bond occurring 7 carbon atoms away from the methyl group. Oleic acid has 18 carbon atoms with the first double bond occurring 9 carbon atoms away from the methyl group. The illustration below shows a molecule of oleic acid. Monounsaturated fats are found in natural foods like nuts and avocados, and are the main component of olive oil (oleic acid). They can also be found in grapeseed oil, ground nut oil, sesame oil and corn oil. Canola oil is 57%−60% monounsaturated fat and olive oil is about 75% monounsaturated fat.
Saturated and unsaturated fats differ in their energy content and melting point. Since an unsaturated fat contains fewer carbon-hydrogen bonds than a saturated fat with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms. Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature. However, the rigid double bond in an unsaturated fat fundamentally changes the chemistry of the fat. The cis-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently like with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. Trans-fats, however, may still stack like saturated fats, but are not as susceptible to metabolization.
Fats function as long-term energy stores
They also serve as energy stores for the body. Fats are broken down in the body to release glycerol and free fatty acids. The glycerol can be converted to glucose by the liver and thus used as a source of energy. The fatty acids are a good source of energy for many tissues, especially heart and skeletal muscle. 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.
what (chemically speaking) makes fats such an efficient energy store?
Adipose or fatty tissue is the human body's means of storing metabolic energy over extended periods of time. Depending on current physiological conditions, adipocytes store fat derived from the diet and liver metabolism or degrades stored fat to supply fatty acids and glycerol to the circulation. These metabolic activities are regulated by several hormones (i.e., insulin, glucagon and epinephrine). The location of the tissue determines its metabolic profile: "Visceral fat" is located within the abdominal wall (i.e., beneath the wall of abdominal muscle) whereas "subcutaneous fat" is located beneath the skin (and includes fat that is located in the abdominal area beneath the skin but above the abdominal muscle wall). It was briefly thought that visceral fat produced a hormone involved in insulin resistance, but this has been disproven by clinical tests (see, resistin, a hormone, ultimately misnamed, which is produced by adipose tissue and does cause insulin resistence in mice but not in humans).
Other biological roles of fats include insulation, transport, and hormone synthesis
Vitamins A, D, E, and K are fat-soluble, meaning they can only be digested, absorbed, and transported in conjunction with fats. Fats are sources of essential fatty acids, an important dietary requirement.
Fats play a vital role in maintaining healthy skin and hair, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function. They are also known as lipids.
Fat also serves as a useful buffer towards a host of diseases. When a particular substance, whether chemical or biotic — reaches unsafe levels in the bloodstream, the body can effectively dilute — or at least maintain equilibrium of — the offending substances by storing it in new fat tissue. This helps to protect vital organs, until such time as the offending substances can be metabolized and/or removed from the body by such means as excretion, urination, accidental or intentional bloodletting, sebum excretion, and hair growth.
Fats in human health and nutrition
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.
Other diseases caused by high triglycerides include pancreatitis and depression.
ReferencesISBN links support NWE through referral fees
- Donatelle, Rebecca J. 2005. Health: The Basics, 6th edition. San Francisco, CA: Pearson.
- Stryer, Lubert. 1995. Biochemistry, 4th edition. New York, NY: W.H. Freeman.
External links
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