Unsaturated fat

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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.

Where double bonds are formed, hydrogen atoms are subtracted from the carbon chain. Thus, a saturated fat has no double bonds, has the maximum number of hydrogens bonded to the carbons, and therefore is "saturated" with hydrogen atoms. In cellular metabolism, unsaturated fat molecules contain somewhat less energy (i.e., fewer 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.

Chemistry and nutrition[edit]

Amounts of fat types in selected foods

Double bonds may be in either a cis or a trans isomer, depending on the geometry of the double bond. In the cis isomer, hydrogen atoms are on the same side of the double bond; whereas in the trans isomer, they are on opposite sides of the double bond (see trans fat). Saturated fats are useful in processed foods because saturated fats are less vulnerable to rancidity and usually more solid at room temperature than unsaturated fats. Unsaturated chains have a lower melting point, hence these molecules increase the fluidity of cell membranes.

Although both monounsaturated and polyunsaturated fats can replace saturated fat in the diet, trans unsaturated fats should not. Replacing saturated fats with unsaturated fats helps lower levels of total cholesterol and LDL cholesterol in the blood.[1] Trans unsaturated fats are an exception because the double bond stereochemistry predisposes the carbon chains to assume a linear conformation, which conforms to rigid packing as in plaque formation. The geometry of the cis double bond induces a bend in the molecule, thereby precluding rigid formations (see Trans fat § Chemistry links above for drawings that illustrate this). Natural sources of fatty acids (see above) are rich in the cis isomer[citation needed].

Although polyunsaturated fats are protective against cardiac arrhythmias, a study of post-menopauseal women with a relatively low fat intake showed that polyunsaturated fat is positively associated with progression of coronary atherosclerosis, whereas monounsaturated fat is not.[2] 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.[3]

Examples of unsaturated fatty acids are palmitoleic acid, oleic acid, myristoleic acid, linoleic acid, and arachidonic acid. Foods containing unsaturated fats include avocado, nuts, olive oils, and vegetable oils such as canola. Meat products contain both saturated and unsaturated fats.

Although unsaturated fats are conventionally regarded as 'healthier' than saturated fats,[4] 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.[5]

In chemical analysis, fatty acids are separated by gas chromatography of methyl esters;[6] additionally, a separation of unsaturated isomers is possible by argentation thin-layer chromatography.[7]

Fat composition in different foods
Fat composition in foods.png
Food Saturated Mono-
unsaturated
Poly-
unsaturated
As weight percent (%) of total fat
Cooking oils
Canola oil 08 64 28
Coconut oil 87 13 00
Corn oil 13 24 59
Cottonseed oil[8] 27 19 54
Olive oil[9] 14 73 11
Palm kernel oil[8] 86 12 02
Palm oil[8] 51 39 10
Peanut oil[10] 17 46 32
Rice bran oil 25 38 37
Safflower oil, high oleic[11] 06 75 14
Safflower oil, linoleic[8][12] 06 14 75
Soybean oil 15 24 58
Sunflower oil[13] 11 20 69
Mustard oil 11 59 21
Dairy products
Butterfat[8] 66 30 04
Cheese, regular 64 29 03
Cheese, light 60 30 00
Ice cream, gourmet 62 29 04
Ice cream, light 62 29 04
Milk, whole 62 28 04
Milk, 2% 62 30 00
*Whipping cream[14] 66 26 05
Meats
Beef 33 38 05
Ground sirloin 38 44 04
Pork chop 35 44 08
Ham 35 49 16
Chicken breast 29 34 21
Chicken 34 23 30
Turkey breast 30 20 30
Turkey drumstick 32 22 30
Fish, orange roughy 23 15 46
Salmon 28 33 28
Hot dog, beef 42 48 05
Hot dog, turkey 28 40 22
Burger, fast food 36 44 06
Cheeseburger, fast food 43 40 07
Breaded chicken sandwich 20 39 32
Grilled chicken sandwich 26 42 20
Sausage, Polish 37 46 11
Sausage, turkey 28 40 22
Pizza, sausage 41 32 20
Pizza, cheese 60 28 05
Nuts
Almonds dry roasted 09 65 21
Cashews dry roasted 20 59 17
Macadamia dry roasted 15 79 02
Peanut dry roasted 14 50 31
Pecans dry roasted 08 62 25
Flaxseeds, ground 08 23 65
Sesame seeds 14 38 44
Soybeans 14 22 57
Sunflower seeds 11 19 66
Walnuts dry roasted 09 23 63
Sweets and baked goods
Candy, chocolate bar 59 33 03
Candy, fruit chews 14 44 38
Cookie, oatmeal raisin 22 47 27
Cookie, chocolate chip 35 42 18
Cake, yellow 60 25 10
Pastry, Danish 50 31 14
Fats added during cooking or at the table
Butter, stick 63 29 03
Butter, whipped 62 29 04
Margarine, stick 18 39 39
Margarine, tub 16 33 49
Margarine, light tub 19 46 33
Lard 39 45 11
Shortening 25 45 26
Chicken fat 30 45 21
Beef fat 41 43 03
Goose fat[15] 33 55 11
Dressing, blue cheese 16 54 25
Dressing, light Italian 14 24 58
Other
Egg yolk fat[16] 36 44 16
Avocado[17] 16 71 13
Unless else specified in boxes, then reference is:[18]
* 3% is trans fats

Role of dietary fats in insulin resistance[edit]

Incidence of Insulin resistance is lowered with diets higher in monounsaturated fats (especially oleic acid), while the opposite is true for diets high in polyunsaturated fats (especially large amounts of arachidonic acid) as well as saturated fats (such as arachidic acid). These ratios can be indexed in the phospholipids of human skeletal muscle and in other tissues as well. This relationship between dietary fats and insulin resistance is presumed secondary to the relationship between insulin resistance and inflammation, which is partially modulated by dietary fat ratios (Omega-3/6/9) with both omega 3 and 9 thought to be anti-inflammatory, and omega 6 pro-inflammatory (as well as by numerous other dietary components, particularly polyphenols and exercise, with both of these anti-inflammatory). Although both pro- and anti-inflammatory types of fat are biologically necessary, fat dietary ratios in most US diets are skewed towards Omega 6, with subsequent disinhibition of inflammation and potentiation of insulin resistance.[5] But this is contrary to the suggestion of more recent studies, in which polyunsaturated fats are shown as protective against insulin resistance.

Membrane composition as a metabolic pacemaker[edit]

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 [19] 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.[20] 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.[19] 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.[21][22]

See also[edit]

References[edit]

  1. ^ Reiner Željko; et al. (28 June 2011). "ESC/EAS Guidelines for the management of dyslipidaemias: the Task Force for the management of dyslipidaemias of the European Society of Cardiology (ESC) and the European Atherosclerosis Society (EAS)". European Heart Journal. 32 (14): 1769–818. doi:10.1016/j.atherosclerosis.2011.06.012. PMID 21723445.
  2. ^ Dariush Mozaffarian; Rimm, EB; Herrington, DM (1 November 2004). "Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women". American Journal of Clinical Nutrition. 80 (5): 1175–84. doi:10.1093/ajcn/80.5.1175. PMC 1270002. PMID 15531663.
  3. ^ B Leibovitz; Hu, ML; Tappel, AL (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. PMID 2303916.
  4. ^ Fats and sugars. BBC Health, retrieved 2013-04-07
  5. ^ a b LH Storlien; Baur, LA; Kriketos, AD; Pan, DA; Cooney, GJ; Jenkins, AB; Calvert, GD; Campbell, LV (1996). "Dietary fats and insulin action". Diabetologia. 39 (6): 621–31. doi:10.1007/BF00418533. PMID 8781757.
  6. ^ Aizpurua-Olaizola, Oier; Ormazabal, Markel; Vallejo, Asier; Olivares, Maitane; Navarro, Patricia; Etxebarria, Nestor; Usobiaga, Aresatz (2015-01-01). "Optimization of Supercritical Fluid Consecutive Extractions of Fatty Acids and Polyphenols from Vitis Vinifera Grape Wastes". Journal of Food Science. 80 (1): E101–E107. doi:10.1111/1750-3841.12715. ISSN 1750-3841.
  7. ^ Breuer B., Stuhlfauth T., Fock H. P. (1987). "Separation of fatty acids or methyl esters including positional and geometric isomers by alumina argentation thin-layer chromatography". J. Chromatogr. Sci. 25: 302–306. doi:10.1093/chromsci/25.7.302.
  8. ^ a b c d e Anderson. "Fatty acid composition of fats and oils" (PDF). UCCS. Retrieved April 8, 2017.
  9. ^ "NDL/FNIC Food Composition Database Home Page". Nal.usda.gov. Retrieved May 21, 2013.
  10. ^ USDA → Basic Report: 04042, Oil, peanut, salad or cooking Retrieved on January 16, 2015
  11. ^ nutritiondata.com → Oil, vegetable safflower, oleic Retrieved on April 10, 2017
  12. ^ nutritiondata.com → Oil, vegetable safflower, linoleic Retrieved on April 10, 2017
  13. ^ nutritiondata.com → Oil, vegetable, sunflower Retrieved on September 27, 2010
  14. ^ USDA Basic Report Cream, fluid, heavy whipping
  15. ^ "Nutrition And Health". The Goose Fat Information Service.
  16. ^ nutritiondata.com → Egg, yolk, raw, fresh Retrieved on August 24, 2009
  17. ^ "09038, Avocados, raw, California". National Nutrient Database for Standard Reference, Release 26. United States Department of Agriculture, Agricultural Research Service. Retrieved 14 August 2014.
  18. ^ "Feinberg School > Nutrition > Nutrition Fact Sheet: Lipids". Northwestern University. Archived from the original on 2011-07-20.
  19. ^ a b Hulbert A.J., Else P.L. (1999). "Membranes as Possible Pacemakers of Metabolism". J. Theor. Biol. 199: 257–274. doi:10.1006/jtbi.1999.0955.
  20. ^ Hulbert A.J., Faulks S., Buttemer W.A., Else P.L. (2002). "Acyl Composition of Muscle Membranes Varies with Body Size in Birds". J. Exp. Biol. 205: 3561–3569.
  21. ^ AJ Hulbert (2003). "Life, death and membrane bilayers". The Journal of Experimental Biology. 206 (Pt 14): 2303–11. doi:10.1242/jeb.00399. PMID 12796449.
  22. ^ Raynard, R.S., Cossins, A.R. 1991. Homeoviscous Adaptation and Thermal Compensation of Sodium Pump of Trout Erythrocytes. Am. J. Physiol. Regul. Integr. Comp. Physiol. 260:R916–R924.