What is a Fat?
Describing Fatty Acids
Fats in the Body
Fats in Food
Health Issues

What is a Fat A fat, or Lipid - is made up of a molecule of glycerol in which one or more of its three original hydroxyl groups have been replaced by fatty acid chains. Approximately 95% of food lipids fall into a group called triglycerides (all three glycerol -OH groups are replaced). Other important lipids are phospholipids (e.g. emulsifying agents such as lecithin) and sterols (e.g cholesterol). Lipids can be liquid at room temperature, as in canola oil, or solid, as in margarine. The nature and properties of lipids are related to the type of fatty acids present. Fatty acids from plants and animals are different - affecting both their physical and chemical properties: Saturated - no double bonds, e.g. acetic acid CH3COOH, (vinegar), lard. Unsaturated Monounsaturated - one double bond, e.g. Oleic acid (Olive oil) C17H33COOH Polyunsaturated - two or more double bonds, e.g. Linolenic acid (Linseed oil) C17H29COOH has three double bonds. Length of carbon chain - acetic acid has a one carbon chain, oleic acid has a 17 carbon chain. Physical Properties - fatty acids from animals are usually highly saturated giving solid fats at room temperature e.g lard. Plant lipids are high in unsaturated fats giving oils at room temperature e.g canola oil, olive oil. Describing Fatty Acids Fatty acids are described by the ratio of the number of carbon atoms in the chain to the number of double bonds and the position of the double bond is thought to have significance in health issues. Linoleic acid is 18:2 omega-6 fatty acid i.e it has an 18 carbon chain, two double bonds and the double bond lies between the sixth and seventh carbon atoms. Linolenic acid is 18:3 omega - 3 fatty acid. Fats in the Body In our body, lipids or fats (fatty acids) have several essential and important functions. Fats store food energy - when metabolized fats release more energy than any other food constituent. i.e. 2.25x more than protein. insulate the body and protect body and organs such as kidneys from damage. are essential parts of cell walls. are necessary for the production of various hormones and vitamin D. are important for the production of sterols which are found in all animals and plants. However, only cholesterol is found in animals. are essential transport agents for fat soluble vitamins around the body tissues. Small amounts of fat are essential for human nutrition. One essential fatty acid, linoleic acid, must be supplied in the diet, since the body cannot produce enough. Linolenic acid and arachidonic acid were once considered essential. However, we now know that the body can convert linoleic acid to arachidonic acid and linolenic acid can only partially replace linoleic acid. These fatty acids are necessary for the production of prostaglandins, thromboxanes and several other compounds. Prostaglandins and thromboxanes affect nearly every physiological system in the body. Sources of Fatty Acids in Food Good food sources of linoleic acid and somewhat lesser amount of linolenic acid, include seed oils from corn, cotton, soybean (50% linoleic acid) and peanuts (20-30% linoleic acid) as well as chicken fat. most other animal fats are low in this essential fatty acid. Linseed oil is an excellent source of linolenic acid. High Fat Foods Source Fat Content Oils, salad, cooking 100% Butter and Margarine 80% Mayonnaise 80% Walnuts 64% Chocolate (unsweetened) 53% Pork sausage (cooked) 45% Cheese 30% Olives 16-20% Cakes, Cookies 10-25% Ice Cream 10-16% Meats 4-15% Health Issues Deficiency symptoms of essential fatty acids include decreased growth, dermatitis, fatty liver, impaired reproduction and impaired water balance. There is evidence omega-3 fatty acids (found in fish) are important in prevention of heart disease. There have been volumes written on the dangers of high cholesterol diets and their effects on coronary heart disease. To understand this problem we must recognise that cholesterol is essential to the normal functioning of our bodies and that there the two types of cholesterol: Dietary Cholesterol - found in animal products (e.g. meat, dairy products, eggs, shellfish) Blood (serum cholesterol) - comes from two sources About 80% is produced in the body by the liver. 20% is influenced by diet through excess calories, fat and dietary cholesterol Keeping blood cholesterol under control is a key factor in reducing the risk of heart disease and stroke. Since the body makes most its cholesterol, high blood levels of this compound may be related to genetic problems or brought on by illness and only partially related to diet. However, it is a good strategy for all of us to reduce the intake of total fat and, specifically, saturated fat. Recommended Maximum Fat Intake Calories 1,600 2,200 2,800 Total fat (grams) 53 73 93