LIPIDS: Fats & Oils

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LIPIDS



q  Fats and Oils belong to a group of compounds called lipids

q  Contains larger proportions of carbon and hydrogen and smaller proportions of oxygen than carbohydrates

q  More concentrated source of energy providing 2.25 times more energy than carbohydrates and proteins

q  Lipids of importance for us are – fatty acids, fats, oils, sterols, phospholipids and lipoproteins

Classification of Lipids

•       Classified on the basis of structure

q  Simple lipids- They constitute more than 98% of food and body fats. It is made up of 3 fatty acids attached to glycerol. They are triglycerides meaning more than 1 type of fatty acid is present in fat, e.g. Cooking oils and butter.

q  Compound lipids- These are fats in which at least one fatty acid is replaced by carbohydrate, protein or phosphorus, i.e. They are fats + non-fat molecule, e.g. Phospholipids, glycolipids and lipoprotein.

q  Derived lipids- They are breakdown products of fats and include diglycerides, monoglycerides, glycerol and fatty acids.

q  Sterols- Not made with fatty acids and glycerol but have a benzene ring structure. These fat-like substances include cholesterol and fat soluble vitamins.

Fatty Acids

·         Consist of chains of carbon atoms with a methyl group (CH3) group at one end and a carboxyl (COOH) group at the other end.

·         May have short chains or long chains (12-22 carbon chains).

·         May be saturated or unsaturated.

·         Saturated fats have single bonds between carbon atoms.

·         Unsaturated fats have one or more double bonds between carbon atoms.

·         Polyunsaturated fats have two or more double bonds

 

Saturated Fatty Acids:

q  Found in animal foods such as meat, butter, cheese and egg yolk

q Found in plant foods such as coconut oil, palm oil and cocoa butter

q Hydrogenated fats used in bakery have high % of saturated fatty acids

q 10% of our total calories should be from saturated fats

q Examples: Stearic acid, palmitic acid etc.

Unsaturated Fatty Acids:

q Two types – MUFA and PUFA

q MUFA has one double bond and helps in lowering blood cholesterol levels. Examples: Oleic acid

q PUFA has two or more double bonds and helps in lowering blood cholesterol levels and prevent coronary heart disease. Examples: Linoleic acid (2 double bonds), linolenic acids ( 3 double bonds), arachidonic acid (4 double bonds)

Phospholipids, Lipoproteins Glycolipids & Cholesterols

q Phospholipids: Composed of fats, phosphoric acid and a nitrogenous base, e.g. Lecithins. Required for formation of brain and nervous tissue and helps in transporting fats throughout body.

q Lipoproteins: Include cyclomicrons, VLDL, LDL and HDL. Are composed of lipids and proteins in varying proportions.

q Glycolipids: They contain glucose or galactose in place of one of the fatty acids in triglyceride molecule.

q Cholesterols: Fat-like substance present in food. Normal blood cholesterol level is 200 mg/100 ml blood. Helps in formation of bile and is an essential constituent of cell membranes.

Functions of Fats

•      Energy: A concentrated source of energy. 1 gm = 9kcal, when oxidized in body. All tissues except brain and central nervous system can utilize fat as a source of energy.

•      Protein sparing action: The kilocalories from fat spare dietary proteins from being oxidized for energy.

•      Thermal insulation: Subcutaneous fat acts as an insulation and helps in retaining body heat.

•      Protection of vital organs: It provides a protective padding to vital organs from mechanical shock and keeps them in place.

•      Absorption of fat soluble vitamins: Necessary for fat soluble vitamins A, D, E and K.

•      Essential fatty acids: An adequate intake of fats/oils is necessary for linoleic and linolenic acids.

•      Satiety value: Fat slows down the secretion of gastric juice and speed of digestion.

•      Synthesis of cell membranes: For all cell membranes

•      Synthesis of hormones: Necessary for some hormones.

Deficiency & Excess of fats

•      Deficiency: Causes deficiency of fatty acids, linoleic  and linolenic acids; which are reqd. for healthy cell membranes.

Leads to eczema and skin lesions; and also deficiency of fat soluble vitamins, and also growth and weight in children.

•      Excess of fats: Causes obesity and excess fat is stored in adipose tissue. Leads to cardiovascular disease as well.

RDA of fats

•      Should not contribute 30% of total kcalories.

•      Kcalories from Saturated fat should not exceed 10% of total calories and at least 10% calories should be provided by PUFA to ensure intake of all essential fatty acids.

•      The cholesterol intake should not exceed 200 mg/day.

•      Variety of cooking oil to be used.

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