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| Sunday, 12 May 2002 |
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Features |  |
| News Business Features Editorial
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Know your fats Fat is the common name used to describe a whole family of compounds, including triglycerides, the phospholipids and sterols. About 95% of fats consumed in the diet are triglycerides. These may be visible (eg. white fat on cuts of meat, cooking oils) or invisible (eg. oils and solid fats used in bakery products, the oil in peanuts, coconut milk). All pure oils and solid fats, have the same caloric value. One gram of fat provides 9 calories of energy which is more than double the amount of calories for the same weight of carbohydrates or proteins. Chemically the triglycerides can be classified, according to their degree of saturation or hydrogenation. Fat molecules may be described as saturated, monounsaturated or polyunsaturated. In fact most foods contain a mixture of saturated and unsaturated fats. Low-fat or no-fat? With all the information on the risks of a high fat diet, it might be easy to forget that fats are actually an essential part of the diet. Research has found that a healthy diet requires at least 15% of calories to be derived from fat. Fats are required for the efficient absorption of the fat soluble vitamins (vitamins A, D, E and K); and also the source of the 2 essential fatty acids which the body cannot manufacture itself. As long as the diet contains linoleic acid and linolenic acid, the two building block fatty acids, the body can manufacture all other omega-3 and omega-6 long chain unsaturated fatty acids that it requires. For this reason, these two substances are known as the essential fatty acids and the best source of these, are generally plant oils. Evidence is not conclusive, but benefits seem to include reduced risk of thrombosis (blood clotting), reduction of triglyceride levels (associated with reduced risk of heart disease and atherosclerosis) and improvements in visual and mental abilities. In summary, the omega-3 fatty acids from plant and marine sources, as well as the omega-6 acids all have slightly different functions and a healthy diet will include rich sources of all three types of these polyunsaturated fatty acids. Fat is also an important source of energy and in a varied diet, helps to regulate appetite. Children under 2 years of age have relatively small appetites in relation to their energy needs, and should not be given low fat diets. Similarly anyone whose appetite is depressed or who finds it difficult to eat bulky, foods may need to eat more fat than required by a normal healthy adult. Fats and cholesterol Saturated and unsaturated fats in the diet have different effects on the cholesterol which is naturally present and circulating in the blood. We now know that saturated fats push up the LDL or bad forms of cholesterol, increasing the risk of heart disease and other cardiovascular diseases. Unsaturated fats decrease the bad LDL cholesterol, and increase levels of the healthy HDL cholesterol. Polyunsaturated fats have a slightly greater effect than the monounsaturated fats. Those with elevated blood cholesterol levels definitely benefit from a low cholesterol, low saturated fat diet but for those with normal blood cholesterol levels, controlling the amount of saturated fat in the diet seems to more important than restricting cholesterol consumption. Monounsaturated fats Monounsaturated fats have a similar effect on blood cholesterol as polyunsaturated fats, but do not produce as many free radicals in the body. Free radicals are damaging to body cells and require antioxidant nutrients to neutralise their effects. Cold-pressed olive oil is rich in both monounsaturated oleic acid and antioxidants and these are thought to be two of the reasons for the health benefits of the traditional 'Mediterranean diet'. In fact, other oils also contain high levels of oleic acid and antioxidants. Plant breeding for example has resulted in the development of high-oleic safflower, sunflower, peanut, canola and soybean oil also. Trans fatty acids There has been much concern about the effect of trans fatty acids on the body. Trans fatty acids are partially unsaturated fats. Their effect on the body is similar to saturated fats in that they raise total bad LDL cholesterol and lower the good HDL cholesterol. Trans fatty naturally occur in small amounts in some foods such as full fat milk and butter. Trans fatty acids are also found in shortening fats, which have been hardened by a process, called hydrogenation. Hydrogenation is used to turn liquid polyunsaturated oils into solid fats in baked goods such as biscuits and pastries. good quality margarines with high levels of polyunsaturated fats contain very low levels of trans fatty acids. Wise shopping choices The food industry has responded to concerns about rising dietary fat intake in many ways. Non-fat food ingredients such as emulsifiers and thickening agents have been developed to replace fats in some processed foods; improved hydrogenation processes have reduced the production of trans fatty acids; nutritional labelling enables consumers to monitor their own total and saturated fat consumption, and in some countries alternative lipids have been developed and marketed to actively reduce levels of bad cholesterol in the blood. Consumers can use these innovations to their advantage: Choose low fat options use information on labels, to check for total fat and proportions of saturated and unsaturated fats, or look at the lists of ingredients which are given in order of weight to check fat content. Low fat tips Eat at least five portions of fruit and vegetables per day Use low fat cooking methods such as grilling or baking instead of frying Choose lean meats and trim all visible fat from meat before cooking Choose low fat dairy foods Use a variety of unsaturated cooking oils and spreads sparingly Check fat content on food labels Avoid high fat foods such as rich pastries, crisps and fried foods Choose oily fish such as tuna, herring, mackerel, and sardines twice a week and white fish regularly also Eat a wide variety of foods Include whole grains beans and nuts in your diet regularly (nuts are high in calories - so limit consumption). Foods contain two main types of fat. They are called saturated and unsaturated fat. Saturated fat Saturated fats are generally those which tend to be hard at room temperature. They are found in animal products including beef, mutton, pork, milk and cheese. Others are egg yolks, shellfish, liver, fish roe, brain, shrimp, kidneys and processed foods such as sausages. Although of vegetable origin, palm and coconut oil are also enormously high in saturated fats. Research has shown that consistently high amounts of saturated fat in your food may increase the level of cholesterol in your blood stream. Polyunsaturated fat Polyunsaturated fats are those which are very soft, or even liquid, at room temperature. They are found naturally in many seeds and nuts; or in products made from these. Margarine made of polyunsaturated oil such as Sunflower oil is a very good example. Fish too - especially 'oily' fish like mackerel - contains polyunsaturated fats. Results of many studies have shown that polyunsaturated fats do not increase blood cholesterol levels and indeed may lower it. |
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