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In the broadest sense, these are lipids that are soluble in alcohol but not water. More specifically they denote a tridlyeride. To the layman, Triglycerides that areliquids at room temperature are called oils; only those that are solids are called fats - although both contain fatty acids; some saturated, some unsaturated.
Fats are the bodies most concentrated source of energy, and are, in fact, the body's energy reserve, supplying 9 calories per gram.
The average British man eats 102g of fat a day and the average woman, 74g. the recommended daily amount is 90g for him and 70g for her.
There are four main types of fat -
1. Hard fats are generally of animal origin, and are composed mainly of saturated fatty acids such as butter and lard.
2. Liquid vegetable oils, such as sunflower, consist mainly of polyunsaturated omega-6 fatty acids, with the exception of palm and coconut oils, which are mostly saturated - and for health reasons should be avoided. Fish oils are also polyunsaturated, but contain omega-3 fatty acids and other beneficial factors, such as reducing LDL 'bad' cholesterol levels and increasing the 'good' HDL variety, and the incidence of heart disease.
3. Monounsaturated - these occur in olives, avocado and some nut oils, making them more stable and less prone to oxidation than polyunsaturated varieties.
4. Trans-fatty acids - these are formed when vegetable oils are processed (hydrogenated), into items such as margarine. Although unsaturated, trans-fatty acids are thought to act like saturated fats in the body.
A certain amount of fat is vital to the body, as it enables the utilisation of the fat-soluble vitamins, A, E, D and K. Fats are the only substance that stimulate gall bladder activity - without which gallstones would be formed - and they are needed to produce hormones that are essential for sexual activity.
Certain types of fats insulate the nerves, ensuring they remain healthy.
Most fatty acids can be produced by the body, but there are three exceptions - linoleic, linolenic and arachidonic acids (vitamin F) - are known as 'essential fatty acids' (EFAs) and must be supplied by food intake. EFAs are required for the function of every cell, tissue, gland and organ. They maintain a healthy and supple skin and produce prostaglandins - hormone-like compounds that reduce blood clotting, lower hypertension and prevent hrart attacks and strokes. EFAs also form red blood cells and promote immunity against disease and are essential for mental function - half the brain is composed of EFAs.
The ideal diet is one in which fat is eaten sparingly, mostly in the form of fresh, unrefined vegetables and marine oils. These fats, in moderation, are thought to help prevent cancer and heart attacks. See' Fat; types of'; ' The French Paradox'; For more information on nutrition see 'Nutrition A to Z' by Dr. Michael Sharon (Prion books)