| Types offats infood |
|---|
| Components |
| Manufactured fats |
Anunsaturated fat is afat orfatty acid in which there is at least onedouble bond within the fatty acid chain, which makes the fatty acid chain, which is basically a chain ofhydrocarbons, analkene. A fatty acid chain ismonounsaturated if it contains one double bond, andpolyunsaturated if it contains more than one double bond.
Asaturated fat has no carbon-to-carbon double bonds, so the maximum possible number of hydrogen is bonded to carbon, and thus, is considered to be "saturated" with hydrogen atoms. To form carbon-to-carbon double bonds,hydrogenatoms are 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 susceptible it becomes tolipid peroxidation (rancidity).Antioxidants can protect unsaturated fat from lipid peroxidation.
In chemical analysis, fats are broken down to their constituent fatty acids, which can be analyzed in various ways. In one approach, fats undergotransesterification to givefatty acid methyl esters (FAMEs), which are amenable to separation and quantitation usinggas 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 acid comprises most of the triunsaturated fatty acid component.
Although polyunsaturated fats are protective againstcardiac arrhythmias, a study of post-menopausal women with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression ofcoronaryatherosclerosis, whereasmonounsaturated fat is not.[4] This probably is an indication of the greater vulnerability of polyunsaturated fats tolipid peroxidation, against whichvitamin E has 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 oils such ascanola.Meat products 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[who?] 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]
Studies on thecell membranes ofmammals andreptiles discovered 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-6 for 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-bloodedness of mammals and birds.[9] However polyunsaturation of cell membranes may also occur in response to chronic cold temperatures as well. Infish increasingly 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]
