Good or bad?

Fats often have a negative connotation, but some fats are essential in the diet. Overall intake of fats should be limited, as weight for weight, they contain more calories than protein, carbohydrate, and even alcohol. However, some vitamins (the fat soluble vitamins A, D, E and K) are found with fat in the diet. Therefore, diets very low in fat may be deficient in these vitamins.

The different kinds of fats you may have heard of are saturated, unsaturated (which includes mono-unsaturated and poly-unsaturated fats, and omega-3, omega-6 and omega-9 fats) and trans fats. These names refer to differences in the chemical structure of the fat, but also reflect differences in where they may be found in the diet.

Saturated Fats

Saturated fats are primarily found in food of animal origin. This includes not just meat lard and animal suet, but also vegetarian foods such as butter and cheese. Saturated fats are often 'hidden' in baked goods, such as cakes, biscuits and pastries. Two vegetable oils (coconut oil and palm oil) also contain significant amounts of saturated fat. You can think of the chemical structure of saturated fat molecules as being like straight sticks (this is because they do not have any 'double bonds' which cause kinks, or bends, in the structure). These 'sticks' pack tightly together, which is why saturated fats tend to be solid at room temperature (like butter and lard).

HIgh levels of saturated fats in the diet are associated with increased risk of certain cancers, and cardiovascular disease.

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Unsaturated Fats

Unsaturated fats are found in foods of plant origin, such as nuts, seeds and vegetable oils. Olive and rapeseed oils are particularly high in monounsaturated fats, whereas sunflower and soya oils are higher in polyunsaturated fats. In terms of chemical structure, unsaturated fats have one or more double bonds, and each of these double bonds causes a kink or bend in the structure. So, unlike the straight stick structure of saturated fats, unsaturated fats resemble a bent stick. Mono-unsaturated fats have one double bond (and therefore one bend) while polyunsaturated fats have more than one double bond, and therefore, more than one bend. The bends prevents the sticks from packing together tightly, and means that unsatured fats are often liquid at room temperature.

Replacing saturated fat with unsaturated fats in your diet should lower your cholesterol levels, and reduce your risk of cardiovascular diseases and some cancers. Don't forget that all fat contains the same amount of calories, so you should still take care over your total fat intake.

Unsaturated fats are also classified according to the position of the first double bond in their structure. This gives rise to the omega-3, omega-6 and omega-9 fats, where omega refers to one end of the molecule, and the number refers to the position of the first double bond, counting from the 'omega' end.

Specific omega-3 fats are called 'alpha linolenic acid' (ALA), 'eicosapentaenoic acid' (EPA), and 'docosahexaenoic acid' (DHA).

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Trans Fats

Trans fats are not present in nature, but are formed during high temperature processing of unsaturated fats, such as hydrogenation. Hydrogenation is used to convert liquid, unsaturated oils, such as sunflower oil, into a more solid fat, such as sunflower spread. In trans fats, the bend in the bent stick fat molecule has an 'N' shape. Regular unsaturated fats have a bend shaped like a 'U'. Our bodies use these differently shaped fat molecules in different ways: trans fats have a similar effect to saturated fats on our health, and therefore should be avoided.

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Please remember, the nutritional information on vegan Volumes' pages are a general guide only. if you are in doubt about your health or diet, consult your doctor or a dietitian.

These pages were last updated 22nd May 2010
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