Unsaturated fat

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Unsaturated fats
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Types of fats in food
Components
Manufactured fats

An unsaturated fat is a fat or fatty acid in which there is at least one double bond within the fatty acid chain. A fatty acid chain is monounsaturated if it contains one double bond, and polyunsaturated if it contains more than one double bond.

A

calories) 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 to lipid peroxidation (rancidity). Antioxidants
can protect unsaturated fat from lipid peroxidation.


Composition of common fats

In chemical analysis, fats are broken down to their constituent fatty acids, which can be analyzed in various ways. In one approach, fats undergo transesterification to give fatty acid methyl esters (FAMEs), which are amenable to separation and quantitation using by gas chromatography.[1] Classically, unsaturated isomers were separated and identified by argentation thin-layer chromatography.[2]

Fatty acid component (mole %) of selected fats[3]
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) and palmitic acids (C16). Monounsaturated fats are almost exclusively oleic acid. Linolenic acid comprises most of the triunsaturated fatty acid component.

Chemistry and nutrition

Amounts of fat types in selected foods

Although polyunsaturated fats are protective against

menopausal women with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression of coronary atherosclerosis, whereas monounsaturated fat is not.[4] This probably is an indication of the greater vulnerability of polyunsaturated fats to lipid peroxidation, against which vitamin E has been shown to be protective.[5]

Examples of unsaturated fatty acids are

canola. Meat
products contain both saturated and unsaturated fats.

Although unsaturated fats are conventionally regarded as 'healthier' than saturated fats,[6] the United States Food and Drug Administration (FDA) recommendation stated that the amount of unsaturated fat consumed should not exceed 30% of one's daily caloric intake.[citation needed] 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.[7]

Membrane composition as a metabolic pacemaker

Studies on the cell membranes of mammals and reptiles discovered that mammalian cell membranes are composed of a higher proportion of polyunsaturated fatty acids (DHA, omega-3 fatty acid) than reptiles.[8] Studies on bird fatty acid composition have noted similar proportions to mammals but with 1/3rd less omega-3 fatty acids as compared to omega-6 for a given body size.[9] 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 concomitant warm-bloodedness of mammals and birds.[8] However polyunsaturation of cell membranes may also occur in response to chronic cold temperatures as well. In fish 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 lower temperatures.[10][11]

See also

Look up unsaturated fat in Wiktionary, the free dictionary.

References

  1. PMID 25471637
    .
  2. PMID 3611285
    .
  3. ISBN 9783527303854
    .
  4. PMID 15531663
    .
  5. PMID 2303916
    .
  6. ^ Fats and sugars. BBC Health, retrieved 2013-04-07
  7. S2CID 33171616
    .
  8. ^
    PMID 10433891
    .
  9. PMID 12364409
    .
  10. PMID 12796449
    .
  11. S2CID 24441498
    .
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