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Fatty acids 'Omega-3 fish oils', PUFAs, HUFAs. These are names much bandied about but little understood. The role of fatty acids in nutrition is complex. In the 1970s the story seemed simple: saturated fats were bad, raised blood cholesterol levels and hence caused heart disease; polyunsaturated fats were good: they lowered cholesterol levels and hence protected against heart disease. This is an oversimplification. Firstly, we need to understand what the terms 'saturated' and 'polyunsaturated' mean. They are terms from organic chemistry, the chemistry of carbon compounds, which includes all living substances. Carbon tends to link to four other atoms. Very many chemical compounds (including fatty acids) consist of long chains of carbon atoms. Compounds with all four links around each carbon atom, occupied by another atom, usually hydrogen, are called saturated. But sometimes there is double link between two carbons in the chain and such compounds are called unsaturated. The double link changes the chemical properties in quite a fundamental way, making the substance more reactive. A polyunsaturated compound simply has several of these double links. Fatty acids are so called because they are essential components of all fats and oils ( a fat is simply an oil that is solid at room temperature). They are carbon-based acids (as opposed to the mineral acids such as sulphuric and nitric). In fats they are compounded with glycerine but it is the fatty acid that gives the fat its special character. Fatty acids can have chains of carbon atoms that are short (less than 8), medium (8-12) or long. The first short-chain fatty acid is none other than vinegar, acetic acid. The interesting fatty acids nutritionally are long chain acids with 18-22 carbon atoms. These are the fatty acids found in milk products, nuts, vegetable and fish oils. All such oils are complex mixtures of fatty acids but particular acids predominate in specific oils, for example oleic acid in olive oil, linoleic acid in corn oil, palmitic acid in palm oil. PUFAs are polyunsaturated fatty acids, that is they have several double linkages; HUFAs are highly unsaturated fatty acids with many double linkages. So where does the omega-3 come in? The omega refers to the position of the double linkage: omega-3 means that the 3rd carbon from the methyl end of the molecule (that's the opposite end to the acid group) has a double linkage. The important omegas to remember in nutrition are omega-3 and omega-6. Omega-6 unsaturated acids include linoleic and arachidonic acids. Most vegetable oils, such as safflower, sesame, soy, corn and sunflower, are rich in various omega-6 acids, principally linoleic, but have virtually no omega-3. The principal omega-3 acids are eicosapentaenoic (EPA) and docosahexaenoic (DHA), found mainly in oily fish such as mackerel, tuna and anchovies. A further omega-3 acid, alpha-linolenic acid (not to be confused with linoleic), is found in some vegetable oils, mainly linseed, canola, walnut, rape and soya. The reason for the current interest in omega-3 oils is that they are important in nourishing the developing brain; so important that human evolution is thought to have involved an essentially fishy diet from the lakes of East Africa. A healthy diet has a balance of omega-3 and omega-6 acids but modern diets are skewed in favour of omega-6. Modern cooking oils are certainly healthier than the saturated fats of butter or margarine but they cannot entirely substitute for fish oils. Omega-3 oil is now added to some foods; it is one of the growing class of functional foods (link): foods that confer a recognised health benefit. All unsaturated chemical compounds are vulnerable to attack by peroxide free radicals. These can damage most living systems and are responsible for initiating many diseases, including cancer and heart disease. Polyunsaturated fatty acids in the body need protection. Antioxidants such as the tocopherols (E306-9, also known as Vitamin E) can do this. Vitamin E is highly polyunsaturated and it simply mops up the dangerous free radicals before they can attack the fatty acids. |