Lipids or fats

Fats are made from one molecule of the trihydric alcohols, namely glycerol attached to three long-chain carboxylic acids (called ‘fatty acids’) of various types. This is a tri fatty acid ester of glycerol and is one of a class of compounds called fats or lipids Phospholipids  are similar to the ester fats but they contain only two fatty acids joined to the glycerol. The other linkage is to a phosphate group.

These compounds form a large part of the molecules making up the cell membranes.
They have specific properties that allow the passage of different molecules through the membranes. Nutrients are allowed to enter and waste products to leave. This is governed by the mechanisms and structures of these compounds amongst others.

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Body fats are the main store of ‘energy’ in the body: 1 g will give 38 kJ of energy when burned. Some foods, like fatty meats, contain these compounds. Fat is stored in adipose tissues in the cells under the skin. It acts as a protective layer or insulator as well as a supplier of energy. It is synthesized in the body mainly from foods rich in carbohydrates. Fats also dissolve the fat-soluble vitamins A and D.
Saturated fatty acids occur in nature in foods as CH3(CH2)nCOOH where n can have a value from 2 to 20. Fatty acids with high n-values are called ‘long-chain fatty acids’. Unsaturated fatty acids are compounds that contain at least one pair of double C C bonds. One such compound occurring in olive oil and pork fat is oleic
acid:

CH3ðCH2Þ7CH CHðCH2Þ7COOH

When these unsaturated oils are treated with hydrogen, heated and the vapours passed over a metallic nickel catalyst, double bonds pick up hydrogen and become saturated. The substance becomes more solid. Margarine is made from polyunsaturatedoils and is treated to loses some of its degree of unsaturation and make it more solid and ‘butter-like’. ‘Soft’ margarine contains more double bonds than the ‘harder’  margarine. The unsaturated bonds are thought to be healthier than the more saturated fats occurring in butter.