Unsaturated fat
| Types offatsinfood |
|---|
| Components |
| Manufactured fats |
Anunsaturated fatis afatorfatty acidin which there is at least onedouble bondwithin the fatty acid chain. A fatty acid chain ismonounsaturatedif it contains one double bond, andpolyunsaturatedif it contains more than one double bond.
Asaturated fathas no carbon to carbon double bonds, so the maximum possible number of hydrogens bonded to the carbons, and is "saturated" with hydrogen atoms. To form carbon to carbon double bonds,hydrogenatomsare removed from the carbon chain. In cellularmetabolism,unsaturated fat molecules contain less energy (i.e., fewercalories) than an equivalent amount of saturated fat. The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is tolipid peroxidation(rancidity).Antioxidantscan protect unsaturated fat from lipid peroxidation.
Composition of common fats[edit]
In chemical analysis, fats are broken down to their constituent fatty acids, which can be analyzed in various ways. In one approach, fats undergotransesterificationto givefatty acid methyl esters(FAMEs), which are amenable to separation and quantitation using bygas chromatography.[1]Classically, unsaturated isomers were separated and identified by argentation thin-layer chromatography.[2]
| fat source | saturated | monounsaturated | doubly unsaturated | triunsaturated |
|---|---|---|---|---|
| Palm kernel | 60–65 | 10–18 | 1–3 | trace |
| Cottonseed oil | 23–30 | 14–21 | 45–58 | trace |
| Corn oil | 10–15 | 25–35 | 40–60 | trace |
| Linseed oil | 8–11 | 18–26 | 14–20 | 51–56 |
| Soybean oil | 11–17 | 18–25 | 49–57 | 6–11 |
| Peanut oil | 12–17 | 35–42 | 39–44 | trace |
| Lard | 36–48 | 36–52 | 10–12 | 1 |
| Beef tallow | 43–64 | 26–45 | 2–6 | 1 |
The saturated fatty acid components are almost exclusively stearic (C18) andpalmitic acids(C16). Monounsaturated fats are almost exclusivelyoleic acid.Linolenic acidcomprises most of the triunsaturated fatty acid component.
Chemistry and nutrition[edit]
Although polyunsaturated fats are protective againstcardiac arrhythmias,a study of post-menopausalwomen with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression ofcoronaryatherosclerosis,whereasmonounsaturated fatis not.[4]This probably is an indication of the greater vulnerability of polyunsaturated fats tolipid peroxidation,against whichvitamin Ehas been shown to be protective.[5]
Examples of unsaturated fatty acids arepalmitoleic acid,oleic acid,myristoleic acid,linoleic acid,andarachidonic acid.Foods containing unsaturated fats includeavocado,nuts,olive oils,andvegetable oilssuch ascanola.Meatproducts contain both saturated and unsaturated fats.
Although unsaturated fats are conventionally regarded as 'healthier' than saturated fats,[6]the United StatesFood and Drug Administration(FDA) recommendation stated that the amount of unsaturated fat consumed should not exceed 30% of one's daily caloric intake.[7]Most foods contain both unsaturated and saturated fats. Marketers advertise only 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.[8]
Membrane composition as a metabolic pacemaker[edit]
Studies on thecell membranesofmammalsandreptilesdiscovered that mammalian cell membranes are composed of a higher proportion of polyunsaturated fatty acids (DHA,Omega -3 fatty acid) thanreptiles.[9]Studies on bird fatty acid composition have noted similar proportions to mammals but with 1/3rd less Omega -3 fatty acids as compared toOmega -6for a given body size.[10]This fatty acid composition results in a more fluid cell membrane but also one that is permeable to various ions (H+ & Na+), resulting in cell membranes that are more costly to maintain. This maintenance cost has been argued to be one of the key causes for the high metabolic rates and concomitantwarm-bloodednessof mammals and birds.[9]However polyunsaturation of cell membranes may also occur in response to chronic cold temperatures as well. Infishincreasingly cold environments lead to increasingly high cell membrane content of both monounsaturated and polyunsaturated fatty acids, to maintain greater membrane fluidity (and functionality) at the lowertemperatures.[11][12]
See also[edit]
- Iodine value– a chemical analysis method to determine the proportion of unsaturated fat.
- List of unsaturated fatty acids
References[edit]
- ^Aizpurua-Olaizola O, Ormazabal M, Vallejo A, Olivares M, Navarro P, Etxebarria N, et al. (January 2015). "Optimization of supercritical fluid consecutive extractions of fatty acids and polyphenols from Vitis vinifera grape wastes".Journal of Food Science.80(1): E101-7.doi:10.1111/1750-3841.12715.PMID25471637.
- ^Breuer B, Stuhlfauth T, Fock HP (July 1987). "Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography".Journal of Chromatographic Science.25(7): 302–6.doi:10.1093/chromsci/25.7.302.PMID3611285.
- ^Thomas, Alfred (2000). "Fats and Fatty Oils".Ullmann's Encyclopedia of Industrial Chemistry.doi:10.1002/14356007.a10_173.ISBN9783527303854.
- ^Mozaffarian D, Rimm EB, Herrington DM (November 2004)."Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women".The American Journal of Clinical Nutrition.80(5): 1175–84.doi:10.1093/ajcn/80.5.1175.PMC1270002.PMID15531663.
- ^Leibovitz B, Hu ML, Tappel AL (January 1990)."Dietary supplements of vitamin E, beta-carotene, coenzyme Q10 and selenium protect tissues against lipid peroxidation in rat tissue slices".The Journal of Nutrition.120(1): 97–104.doi:10.1093/jn/120.1.97.PMID2303916.
- ^Fats and sugars.BBC Health, retrieved 2013-04-07
- ^"Fat Facts, the Right Amount for a Healthy Diet".extension.psu.edu.Retrieved2024-06-03.
- ^Storlien LH, Baur LA, Kriketos AD, Pan DA, Cooney GJ, Jenkins AB, et al. (June 1996). "Dietary fats and insulin action".Diabetologia.39(6): 621–31.doi:10.1007/BF00418533.PMID8781757.S2CID33171616.
- ^abHulbert AJ, Else PL (August 1999). "Membranes as possible pacemakers of metabolism".Journal of Theoretical Biology.199(3): 257–74.Bibcode:1999JThBi.199..257H.doi:10.1006/jtbi.1999.0955.PMID10433891.
- ^Hulbert AJ, Faulks S, Buttemer WA, Else PL (November 2002). "Acyl composition of muscle membranes varies with body size in birds".The Journal of Experimental Biology.205(Pt 22): 3561–9.doi:10.1242/jeb.205.22.3561.PMID12364409.
- ^Hulbert AJ (July 2003)."Life, death and membrane bilayers".The Journal of Experimental Biology.206(Pt 14): 2303–11.doi:10.1242/jeb.00399.PMID12796449.
- ^Raynard RS, Cossins AR (May 1991). "Homeoviscous adaptation and thermal compensation of sodium pump of trout erythrocytes".The American Journal of Physiology.260(5 Pt 2): R916–24.doi:10.1152/ajpregu.1991.260.5.R916.PMID2035703.S2CID24441498.