Unsaturated fat

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Types of fats in food
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An unsaturated fat fat or fatty acid in which there are one or more double bonds in the fatty acid chain. A fat molecule 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 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 (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation. Unsaturated fats also have a more enlarged shape than saturated fats.

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[edit] Chemistry and Nutrition

Amounts of fat types in selected foods (click to enlarge).
Amounts of fat types in selected foods (click to enlarge).

Double bonds may be in either a cis or trans isomer, depending on the geometry of the double bond. In the cis conformation hydrogens 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 processed foods because they are less vulnerable to rancidity and are generally more solid at room temperature than unsaturated fats. Unsaturated chains have a lower melting point, hence increasing fluidity of the cell membranes.

Both mono- 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 bad because the double bond stereochemistry allows the fat molecules to assume a linear conformation which leads to efficient packing (i.e., 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.

Although polyunsaturated fats are protective against cardiac arrhythmias a study of post-menopauseal women with a relatively low fat intake showed that polyunsaturated fat was positively associated with progression of coronary atherosclerosis, whereas monounsaturated fat was not [1]. 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 [2].

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

Although unsaturated fats are healthier than saturated fats,[3] 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 makes up the majority. Thus, various unsaturated fat vegetable oils, such as olive oils, also contain saturated fat.


[edit] The Role of Dietary Fats in the Prevention of Prostate Cancer

Over the years dietary fats have received a lot of attention from the media because of their association with increased risks of heart disease (all facts and citations in this article are from the guide, Nutritional Prevention of Prostate Cancer, found at http://www.PreventProstateCancer.info). Due to this publicity, saturated and trans-fats have become known as bad fats while monounsaturated and polyunsaturated fats are considered good fats. How does this all fit in with the risks of Prostate Cancer?

Well, researchers have found little to no association between total fat, saturated fat, trans-fats, and monounsaturated fats with increased risks of prostate cancer. However, many studies show a relationship between prostate cancer and the consumption of some polyunsaturated fats. Polyunsaturated fats include the omega-3 and omega-6 fatty acids such as alpha-linolenic acid (ALA), linoleic acid (LA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA).

Studies have shown that high levels of ALA consumption, in the form of red meats and dairy products, is associated with increased risks of prostate cancer, while consumption of DHA and EPA from fatty ocean fish is associated with decreased risk of prostate cancer. In fact, one study in particular showed that eating 3 servings of fatty fish per week resulted in a significant decrease in risk. However consumption of greater than 3 servings per week showed light increases in risk, especially in patients whose cancer had metastasized to other areas of the body.

Research has shown that it is the consumption of cold water fatty fish such as salmon, herring, mackerel, anchovies, and sardines that provide the protection against prostate cancer. Studies evaluating the effects of supplementation of DHA and EPA in the form of fish oils have no association with decreased risks. It is commonly believed that fish rather than fish oils contain other preventative compounds such as vitamin D and retinol (Vitamin A) that aid in the prevention of cancer.

With all of that said, it is important to note that ALA is an essential fatty acid and therefore should not be completely eliminated from the diet. Essential fats like ALA and LA are vital to the body, and must be obtained through the diet because the human body is incapable of making them out of other substances. Therefore you should not eliminate all sources of ALA from your diet.

Lastly, in most studies, risks of prostate cancer were only associated with animal sources of ALA, while other studies showed an association with both non-animal (vegetable oils) and animal sources (red meat and dairy). Despite this discrepancy in results, it is clear that diets high in red meat and dairy products contain high levels of ALA; they are the primary risk of prostate cancer. Therefore, replacing red meat with fatty fish a couple of times a week is a good way to reduce your risks of prostate cancer.

Insulin resistance correlates positively with monounsaturated fat (especially oleic acid) and negatively with polyunsaturated fat (especially arachidonic acid) in the phospholipids of human skeletal muscle [4].

[edit] Membrane composition as a metabolic pacemaker

Cell membranes of mammals have a higher composition of polyunsaturated fat (DHA, omega-3 fatty acid) and a lower composition of monounsaturated fat than do reptiles. Higher polyunsaturated membrane content gives greater membrane fluidity (and functionality), commensurate with the higher 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[5]

[edit] References

  1. ^ Dariush Mozaffarian (2004). "Dietary fats, carbohydrate, and progression of coronary atherosclerosis in postmenopausal women". American Journal of Clinical Nutrition 80 (5): 1175–1184. PMID 15531663. 
  2. ^ B Leibovitz (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. 
  3. ^ BBC Health, retrieved June 6, 2007.]
  4. ^ LH Storlien (1996). "Dietary fats and insulin action". Diabetologica 39 (6): 621–631. PMID 8781757. 
  5. ^ AJ Hulbert (2003). "Life, death and membrane bilayers". The Journal of Experimental Biology 206: 2303–2311. PMID 12796449. 

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[edit] External links

Cnjanis (talk) 18:55, 26 May 2008 (UTC)