Why the fuss about fats?

Fat is a nutrient with important functions:

• It is a rich source of energy, providing more than double that of either carbohydrate or protein.
• It is a carrier for the fat-soluble vitamins - A, D, E and K.
• It provides the essential fatty acids, linoleic and alpha-linolenic acid, which are polyunsaturated.

To remain healthy, we need moderate amounts of the right type of fats eaten as part of a good, balanced diet. However, a high fat intake - and in particular, a high intake of saturated fats - is associated with raised blood cholesterol and coronary heart disease.

Not all fats are the same
Fats are made up of fatty acids and glycerol. A fatty acid consists of a chain of carbon atoms, where each carbon atom in the chain is attached to hydrogen atoms. The number of hydrogen atoms per carbon atom determines whether the fatty acid is saturated or unsaturated.

Saturated fats
If a fatty acid has all of the hydrogen atoms it can hold (2 per carbon atom in the chain) and all of the carbon atoms in the chain are linked by single bonds, it is described as saturated. Saturated fats are usually solid or semi-solid at room temperature, and are strongly associated with raised blood cholesterol - which is why nutritionists recommend eating them as little as possible.

Lard, butter, hard cheeses, whole milk, animal fats and palm and coconut oils - plus products containing them - all contain high levels of saturated fat.

Monounsaturated fats
If a pair of carbon atoms in the fatty acid chain is linked by a double bond instead of a single bond, the fatty acid is described as monounsaturated. Fats rich in monounsaturates tend to be liquid at room temperature. Olive oil is one of the richest sources of monounsaturated fatty acids.

Polyunsaturated fats
These contain more than one double bond and are liquid at room temperature. The main sources are vegetable oils, such as sunflower oil, corn oil and rapeseed, but not tropical oils such as coconut, palm and palm kernel oils.

Trans fats
Trans fats are created when a hydrogenation process is applied to solidify oil for use in margarines or to improve a product's shelf life. This processing causes trans fats to act like saturated fats.

Fats and Cholesterol

Cholesterol is a substance which has some important functions in our bodies. However, in excess it can build up in the artery walls and this can lead to risk of heart attack and stroke.

There are actually two types of cholesterol in our blood: LDL-cholesterol and HDL-cholesterol. LDL-cholesterol is sometimes described as 'bad' cholesterol because it is the form that becomes deposited in arteries. HDL-cholesterol, on the other hand, is described as 'good' cholesterol because it is destined to be eliminated from the body. Although the total level of cholesterol in our blood is an indicator of our risk for heart disease, the ratio of LDL to HDL is also important. Ideally, we should keep our total levels of cholesterol low, but within this, the proportion of HDL should be high.

We eat very little cholesterol in our diet and it does not have a significant impact on our blood cholesterol levels. However, our blood cholesterol levels are influenced by the type of fat we eat, especially our consumption of saturated and unsaturated fats.

Saturated fats are well known to raise total cholesterol and LDL-cholesterol levels and are therefore harmful if eaten to excess.
Polyunsaturated fats lower total cholesterol and lower LDL-cholesterol, but they also lower HDL-cholesterol, so their effects are only partly beneficial.
Monounsaturated fats lower total cholesterol and LDL-cholesterol, but have no effect on HDL-cholesterol. This is ideal, because not only do they lower blood cholesterol, but they also improve the ratio between LDL and HDL.