When I look at a food label, there are different types of fats listed, such as saturated and unsaturated fats. Can you explain more about the differences between the types of fats?

There are two main sorts of fats.

• Saturated fats are mainly of animal origin. They are the bad fats and it is the saturated fat that raises your cholesterol levels.

• Unsaturated fats are mainly of vegetable origin and they lower your cholesterol levels.

Saturated fats are a mixture of alcohol, glycerol and fatty acids. The fatty acids contain long chains of carbon atoms - most commonly 12, 14 or 16. These are the most effective at raising the LDL ('bad cholesterol') in the blood. The more saturated fat we eat, the higher the cholesterol; if we eat less, our cholesterol will fall over 3-4 weeks. Unsaturated fats contain carbon atoms that are joined (with double bonds) at certain points; this leads to the fats being liquid or soft at room temperature. When there is one double bond, the fat is monounsaturated; when there are two or more, it is polyunsaturated. Monounsaturated fats include olive, rapeseed and peanut oils and are contained in avocados, almonds and oily fish. Polyunsaturated fats include sunflower oil and most soft margarines (always read the label!). Polyunsaturated fats help prevent blood clots forming, which is another benefit in addition to their cholesterol-lowering effect.

As well as lowering your LDL (bad) cholesterol by switching you away from saturated fat, unsaturated fats also appear to have an additional good effect on lowering cholesterol. Monounsaturated fat may raise the HDL (good) cholesterol as well. All kinds of fat, whether saturated or unsaturated, are rich in calories, so you need to bear in mind, when you change to a healthy diet, not to go overboard on unsaturated fat.

Chapter 9 gives lots of information about which foods contain the different types of fats and gives you lists from which you can choose a healthy diet.

The media has also talked about the harmful effects of trans fatty acids. How can I avoid them?

Trans fatty acids are present in small quantities in meat and dairy products but are present in larger quantities in those oils which have been manufactured to be firmer at room temperature (i.e. when oils have been made into margarines or spreads) by a process known as hydrogenation. Trans fatty acids raise LDL and lower HDL cholesterol levels. When you are selecting vegetable oils and margarine it is important to look for the trans content. The best oils are blended vegetable oils, rapeseed oil and soft margarines that are low in saturates and trans fatty acids, but high in polyunsaturates and mono-unsaturates (see the question above). Always read the margarine label.

The article that I read also mentioned vitamin E as being beneficial. Why is it important?

Vitamin E is an antioxidant; antioxidants help protect the body from free radicals'. Free radicals are produced by some of the normal chemical reactions in the body cells. They are unstable and, in excess, can damage the lining of the cells by oxidising LDL ('bad') cholesterol, causing it to stick to the walls of the arteries.

Antioxidants are present in fruit and vegetables and can prevent cholesterol being oxidised so that it does not tend to stick to the artery wall.

Some early studies suggested that vitamin E protects against heart disease, but unfortunately subsequent studies have not shown any benefit from tablet supplements. Vitamin E is present in food containing a lot of polyunsaturates, such as vegetable oils (especially sunflower) and deep green leafy vegetables. Nuts and vegetable oils, although good sources of vitamin E, are also high in calories, so these should not be eaten too frequently. There is a small amount of vitamin E in wholemeal bread. Some margarines are enriched with vitamin E. If your food intake is high in polyunsaturates, it will contain a lot of vitamin E. Because some of the major sources are high in calories, you may be advised to take extra vitamin E as supplementary tablets by some specialists to avoid putting on weight, but for most of us this will not be necessary. Chemists and health food shops sell vitamin E preparations and the recommended dose is 100-200 units a day (70-140 mg). However, as vitamin supplements have been shown to be of no benefit - save your money!

 
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