Unsaturated fat: Difference between revisions
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John Nowak |
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{{Fats}} |
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An '''unsaturated fat''' is a [[fat]] or [[fatty acid]] in which there are one or more [[double bond]]s in the fatty acid chain. A fat [[molecule]] is [[Monounsaturated fat|monounsaturated]] if it contains one double bond, and [[polyunsaturated]] if it contains more than one double bond. Where double bonds are formed, [[hydrogen]] [[atom]]s are eliminated. Thus, a [[saturated fat]] is "saturated" with hydrogen atoms. In cellular [[metabolism]] hydrogen-carbon bonds are broken down - or [[oxidized]] - to produce energy, thus an unsaturated fat molecule contains somewhat less energy (i.e fewer [[calories]]) than a comparable sized saturated fat. The greater the degree of unsaturation in a fatty acid (ie, the more double bonds in the fatty acid), the more vulnerable it is to [[lipid peroxidation]] ([[rancidification|rancidity]]). [[Antioxidant]]s can protect unsaturated fat from lipid peroxidation. Unsaturated fats also have a more enlarged shape than saturated fats.{{Fact|date=August 2008}} |
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==Chemistry and Nutrition== |
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[[Image:Fatchart.svg|thumb|right|Amounts of fat types in selected foods (click to enlarge).]] |
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Double bonds may be in either a [[Cis-trans isomerism|''cis'' or a ''trans'' isomer]], depending on the [[molecular geometry|geometry]] of the double bond. In the ''cis'' [[Conformational isomerism|conformation]] hydrogen atoms are on the same side of the double bond, whereas in the ''trans'' conformation they are on opposite sides (see also [[Trans fat]]). [[Saturated fats]] are popular with manufacturers of [[Food preservation|processed foods]] because they are less vulnerable to rancidity and are generally more solid at room [[temperature]] than [[Unsaturated fat|''unsaturated'' fats]]. Unsaturated chains have a lower melting point, hence increasing fluidity of the [[Cell (biology)|cell]] [[cell membrane|membrane]]s. |
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Although both monosaturated and polyunsaturated fats can replace saturated fat in the diet, trans unsaturated fats should be avoided. Substituting (replacing) saturated fats with unsaturated fats helps to lower levels of total [[cholesterol]] and LDL cholesterol in the [[blood]]. Trans unsaturated fats are particularly risky because the double bond [[stereochemistry]] allows the fat molecules to assume a linear conformation which leads to efficient packing (i.e., [[Atheroma|plaque]] formation). The geometry of the cis double bond introduces a bend in the molecule precluding stable formations (see specific fatty acid links above for drawings that illustrate this). Natural sources of fatty acids (see above) are rich in the cis isomer. |
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Although polyunsaturated fats are protective against [[cardiac arrhythmia]]s, a study of post-[[menopause]]al women with a relatively low fat intake showed that polyunsaturated fat was positively associated with progression of [[coronary]] [[atherosclerosis]], whereas monounsaturated fat was not <ref>{{cite journal | author=Dariush Mozaffarian | title=Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women | journal=American Journal of Clinical Nutrition | year=2004 | volume=80 | issue=5 | pages=1175–1184 |url=http://www.ajcn.org/cgi/content/full/80/5/1175 | pmid=15531663 | month=Nov | day=01}}</ref>. This probably is an indication of the greater vulnerability of polyunsaturated fats to [[lipid peroxidation]], against which [[Vitamin E|Vitamin E]] has been shown to be protective <ref>{{cite journal | author=B Leibovitz | title=Dietary supplements of vitamin E, beta-carotene, coenzyme Q10 and selenium protect tissues against lipid peroxidation in rat tissue slices | journal=The Journal of Nutrition | year=1990 | volume=120 | issue=1 | pages=97–104 | pmid=2303916}}</ref>. |
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Examples of unsaturated fats are [[palmitoleic acid]], [[oleic acid]], [[myristoleic acid]], [[linoleic acid]], and [[arachidonic acid]]. Foods containing unsaturated fats include [[avocado]], nuts, and vegetable oils such as [[canola]], and [[olive]] [[oil]]s. Meat products contain both saturated and unsaturated fats. |
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Although unsaturated fats are healthier than saturated fats,<ref>[http://www.bbc.co.uk/health/healthy_living/nutrition/basics_fatsugar.shtml BBC Health], retrieved June 6, 2007.]</ref> the old [[Food and Drug Administration]] (FDA) recommendation stated that the amount of unsaturated fat consumed should not exceed 30% of one's daily caloric intake (or 67 grams given a 2000 calorie diet). The new dietary guidelines have eliminated this recommendation. Most food contain both unsaturated and saturated fats. Marketers only advertise one or the other, depending on which one makes up the majority. Thus, various unsaturated fat vegetable oils, such as olive oils, also contain saturated fat. |
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== The Role of Dietary Fats in the Prevention of Prostate Cancer == |
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[[Insulin resistance]] correlates positively with monounsaturated fat (especially oleic acid) and negatively with polyunsaturated fat (especially [[arachidonic acid]]) in the [[phospholipid]]s of human [[skeletal muscle]] <ref>{{cite journal | author=LH Storlien | title=Dietary fats and insulin action | journal=Diabetologica | year=1996 | volume=39 | issue=6 | pages=621–631 | pmid=8781757 | doi=10.1007/BF00418533}}</ref>. |
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==Membrane composition as a metabolic pacemaker== |
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[[Cell membrane]]s of [[mammal]]s have a higher composition of polyunsaturated fat ([[Docosahexaenoic acid|DHA]], [[omega-3 fatty acid]]) and a lower composition of monounsaturated fat than do [[reptile]]s. Higher polyunsaturated membrane content gives greater membrane fluidity (and functionality), commensurate with the higher [[metabolism|metabolic rate]] of the [[warm-blooded]] [[species]]. In [[fish]], however, increasingly cold environments lead to increasingly high cell membrane content of both monounsaturated and polyunsaturated fatty acids, presumably to maintain greater membrane fluidity (and functionality) at the lower [[temperatures]]<ref>{{cite journal | author=AJ Hulbert | title=Life, death and membrane bilayers | journal=The Journal of Experimental Biology | year=2003 | volume=206 | pages= 2303–2311 | url=http://jeb.biologists.org/cgi/content/full/206/14/2303 | pmid=12796449 | doi=10.1242/jeb.00399}}</ref> |
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==References== |
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<div class="references-small"> |
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<references/></div> |
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==See also== |
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* [[Saturated fat]] |
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* [[Monounsaturated fat]] |
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* [[Polyunsaturated fat]] |
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* [[Trans fat]] |
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* [[Iodine number]] - a chemical analysis method to determine the proportion of unsaturated fat. |
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{{lipids}} |
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[[Category:Food science]] |
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[[Category:Carboxylic acids]] |
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[[Category:Fatty acids|#]] |
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[[Category:Lipids]] |
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[[Category:Nutrition]] |
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[[es:Ácido graso insaturado]] |
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[[fr:Acide gras insaturé]] |
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[[ko:불포화 지방산]] |
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[[nl:Onverzadigd vet]] |
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[[ja:不飽和脂肪酸]] |
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[[no:Umettet fett]] |
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[[pt:Gordura insaturada]] |
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[[simple:Unsaturated fat]] |
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[[fi:Tyydyttymätön rasvahappo]] |
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[[sv:Enkelomättat fett]] |
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Revision as of 14:59, 5 March 2009
John Nowak