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Nutrition: Fat

Saturated Fats

Fats in your diet are often divided into two types: visible and invisible. Visible fats are those that are obvious, such as butter, margarine and other spreads, cooking oils and fat on meat. Invisible (hidden) fats are incorporated during cooking (for example, in cakes and biscuits) or during food preparation (as in sausages). Emulsions of fat are used extensively in products such as mayonnaise. Some foods such as eggs are also rich in fat.

Why You Need Fats

A lot is written about the harmful effects of fat. But fat is an essential part of your diet for three reasons. Fat means palatability. Yes, fat makes many foods taste better. It's no use a food being nutritious if people don't like it and therefore won't eat it. Fat provides energy. Fats are a concentrated source of energy, providing nine kcal per gram (38 kj per gram). Fats are also essential nutrients. Fat in your diet provides fat-soluble vitamins and essential fatty acids.

If your diet does not provide enough energy, your body will eventually use functional body proteins (proteins that are incorporated into the essential structure of your body). Your body can adapt to a lack of protein in the short term. However, conditions such as injury, infection, cancer, uncontrolled diabetes and starvation can cause substantial protein losses. In these circumstances, the body starts to lose muscle in order to generate enough energy. If left unchecked, this can become life threatening.

What are Fats?

The basic building blocks of fat are fatty acids and glycerol. A fatty acid is made up of a chain of carbon atoms with an acid group at one end and a methyl group at the other. A methyl group consists of one carbon atom and three hydrogens. Three different fatty acids combine with glycerol to form a triglyceride. The fat in your food is made up of a mixture of triglycerides. The amount and type of fatty acids you eat influence the way in which your body handles them and therefore their role in diseases such as coronary heart disease. Each carbon atom in a fatty acid chain is attached to one or two hydrogen atoms. If the fatty acid has all the hydrogen atoms that it can hold, it is said to be saturated. If, however, some hydrogen atoms are missing, the fatty acid is said to be unsaturated. In unsaturated fats, the missing hydrogen atoms are replaced by a double bond between the carbon atoms. All fats contain both saturated and unsaturated fatty acids, but their relative proportions give fat its predominant characteristics (for example, oil or solid). The level of saturation of a fat is also referred to as hydrogenation. It is possible to alter this level of saturation (or hydrogenation) in the manufacture of fats and oils.