In recent years fats have become the ‘villains’ of the food world. Some people go to great lengths to calcu-late the cholesterol content and the ratio of saturated to unsaturated fatty acids in their foods. Whatever the details, however, there is one piece of nutritional advice that experts agree on and that all of us should heed: eating too much fat is bad for health. This is not to say, however, that any fat is bad for you. Taken in the right amounts, the right sorts of fat are an extremely important part of your diet. Fats provide the human body with the most concentrated source of energy of all dietary elements. Each gram of fat con-tains twice as many calories as a gram of either carbo-hydrate or protein. In addition, fats make other foodstuffs more palatable by contributing to the overall taste and smell of the food. Bread and its well-known fatty companion, butter, are generally considered easier and pleasanter to eat than bread on its own. Fats act both as lubricants for other foods and as ‘carriers’ of certain vitamins which are soluble only in fat. Fatty tissues even help protect some parts of the body from accidental injury. For exemple, the kidneys, liver and heart are surrounded by layers of protective, shock-absorbent fat. And the fatty ma-terial called adipose tissue, which lies just below the skin, acts as an insulating layer to help conserve body heat. Altogether, about ten per cent of body weight is fat. In general, women have a higher proportion of fat in their bodies than men.
Fats are made up of two different types of chemical -glycerol (a sticky liquid popularly known as glycerine) and fatty acids. In the common fats, each molecule is composed of three molecules of fatty acid joined to one molecule of glycerol. Because of this they are also known as triglycerides. Although the glycerol molecule is the same in all fats, the fatty acids attached to it vary considerably. As many as 40 different fatty acids are known to occur in different fats, though generally only 16 of these are present in the fats we eat. The fatty acids attached to glycerol can be either ‘saturated’ or ‘unsaturated’. Saturated fatty acids consist of long chains of carbon atoms, with two hydrogen atoms attached to each carbon atom along the chain. Fats that contain a high proportion of saturated fatty acids are mostly hard or solid at room temperatures. They are found mainly in animal and dairy products, such as lard, suet, bacon fat, butter and cream.
In unsaturated fatty acids not all of the carbon atoms along the length of the chain have two hydrogen atoms. Fatty acids with more than one unsaturated carbon atom are known as ‘polyunsaturated’. Polyun-saturated fats are normally liquid at room tempera-tures and are commonly referred to as oils. They are found naturally in many plant materials, especially nuts and seeds such as corn oil, olive oil, soya bean oil, sunflower oil and rape seed oil. Fish, too – espe-cially the meat of ‘oily’ fishes such as tuna, herring and mackerel – contain polyunsaturated fats. Some of the polyunsurated fats provide your body with ‘essential’ fatty acids. These are substances your body cannot produce itself but which it needs for good health. Linoleic, linolenic and arachidonic acids are polyunsurated fatty acids considered essential for growth and development, and for this reason fats are important in the diets of children.
How much fat do we need?
The amount of dietary fat you need to remain healthy cannot be stated definitively. The smallest amount needed to make the rest of your food palatable is usually from 15 to 20 per cent of the total energy intake. Ideally, a diet of 3,000 Calories should contain at least 75 grams of fat (700 Calories). If you are carrying out a lot of physical activity, or if you are exposed to extremely cold weather, then you need more fat. After you have eaten a fat-containing meal, excess fat which cannot be used is conveyed through the bloodstream to the adipose (fatty) tissues where it is stored. This reserve fat can be used to provide energy when needed.
Several years ago, cholesterol was the centre of medical attention. This fatlike substance which your body can make in the liver is essential for the manufacture of bile acids and certain hormones. High levels of cholesterol in the blood, however, are associated with hardening and narrowing of the arteries (atherosclerosis) and consequent cardiovascular disease. Recent research suggests that eating large amounts of saturated fatty acids increases blood cholesterol levels; on the other hand, a diet rich in polyunsaturated fats may reduce blood cholesterol. But whether eating a high ratio of unsaturated to saturated fats actually decreases one’s chances of suffering from heart disease is hotly debated. Other factors related to heredity and how each person’s body uses cholesterol may be equally important.
In some people, particularly overweight middleaged women (traditionally described as ‘fair, fat and forty’), excess cholesterol in the body accumulates in the gall bladder and forms gallstones. If you are the sort of person who likes fatty foods and you want to do something about becoming ‘healthier’, then perhaps the best advice is to cut down on all fats, including saturated fat and cholesterol. Apart from the obvious fats mentioned above, you may be eating quite considerable quantities of fats without knowing it in such foods as bread, biscuits and cakes. It is not necessary to avoid any foods completely. Indeed, many fat- or cholesterol-rich foods (such as liver) are nutritionally important because they also provide a source of vitamins, minerals and proteins. But you should be aware that some margarines and cooking oils may contain quite high levels of saturated fat. Many margarines, for example, are made from vegetable and fish oils by turning the fats from unsaturated to saturated. Palm and coconut oils are both rich in saturated fat. You may therefore need to look on the labels of cooking-oil bottles and margarine packs and select those ‘high in polyunsaturates’. Low-fat spreads contain about half the number of calories as ordinary margarine or butter. They can therefore be used as substitutes if you are trying to lose weight. These ‘slimming’ spreads contain at least 50 per cent water, as against 15 per cent water in butter or ordinary margarine.