WHAT DO FATTY ACIDS LOOK LIKE? CIS AND TRANS FATTY ACIDS
To further complicate the picture, the unsaturated fats can be classified as cis or trans and this difference also has health effects. Fatty acids that contain a double bond can align themselves in two different geometric formations. If the hydrogen atoms attached to the carbons that have formed a double bond with each other are on the same side of the molecule, the molecule is called cis. If they are on opposite sides, they are called trans. The cis or trans configuration determines the fate of the molecule within the body.
The trans tatty acids are stiffer and tend to act more like saturated fat in the body, raising blood cholesterol levels. Trans fatty acids occur naturally (e.g. about 5 per cent in butter), or from processing (up to 15 per cent in margarine). The studies which have recently dulled the halo over polyunsaturated fats were done in the US and based on American diets in the 1970s when the harder ‘stick’ margarines were used. These are much higher in trans fatty acid content than the softer table margarines now in use. Manufacturers are likely to lower the trans fatty acid content of foods even further in the future.
We have touched on a few of the metabolic consequences of the type of fat in the diet. As well as affecting blood cholesterol, clotting and inflammation, they may also affect other processes such as insulin and glucose metabolism and tumour formation. For body fat storage, the type of fat is of limited importance and the total amount of fat is still regarded as the most important.
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