by G. Lee

Created on: October 01, 2007

There is now considerable evidence that if high levels of serum cholesterol and coronary heart disease are causally related to the intake of fat, the relationship applies only or chiefly to high intake of saturated fats, whereas unsaturated fats tend to reduce the serum cholesterol concentration and may possibly protect against heart disease.

The fatty acids are classified as saturated and unsaturated, and the correspondingly neutral fats formed by their combination with glycerol are termed saturated fats and unsaturated fats, respectively. The saturated fatty acids contain only one single-bond carbon linkages and are relatively least active chemically. The 16-carbon palmitic and 18-carbon stearic acids are the common fatty acids found in most animal and vegetable oils. Coconut oil contains the saturated lauric acid (12-carbon) and myristic acid (14-carbon).

The unsaturated fatty acids contain one or more double-bond carbon linkages and are more reactive to chemical agents than saturated fatty acids. The unsaturated fatty acids are usually of lower melting point than the saturated, and hence as a rule the saturated fats are likely to be solid, whereas the unsaturated fats are oils. When there is only one double-bond carbon linkage, the fatty acid is monounsaturated, as exemplified by the 18-carbon oleic acid. When there is more than one double bond, the fatty acid is polyunsaturated. The common polyunsaturated fatty acids are linoleic, linolenic and arachidonic, containing respectively two, three and four double bonds. In the body the highest percentage of polyunsaturated fatty acids is in the cholesterol ester fraction of the lipids; in the phospholipids there are approximately equal proportions of saturated and unsaturated fatty acids, whereas the percentage in the triglyceride fractions mirrors that in the dietary intake.

The iodine value or iodine number of a fat represents the number of grams of iodine absorbed by 100 grams of fat, a reaction which occurs at the site of the double-bond carbon linkage. Therefore the higher the iodine number, the greater the degree of unsaturation. Fats in diets which are found to be effective in reducing serum cholesterol are so polyunsaturated that they have an iodine value of more than 90. Soybean oil has an iodine value of 130 and cottonseed oil 110, whereas hydrogenated shortenings have a value of 65 to 75 and butter fat 30 to 40.

Essential unsaturated fatty acids are those required for human nutrition and which must be

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