Cholesterol

Cholesterol is not itself fat, but a fat-soluble substance that normally combines with fats in the blood. It is essential to the human body but there is no need for us to consume it in our diet because the body itself can usually manufacture enough to meet its needs for cellular health, good digestion, hormone production and other bodily functions.

Because it does not dissolve in the blood, cholesterol is transported around the body by linking with fat and protein to form a lipoprotein. It is the proportion of cholesterol to protein in these combination molecules that determines their effect on the body. If the cholesterol proportion is high, the density decreases. Low Density Lipoproteins (LDLs) tend to clump together and cling to the walls of the arteries, forming a thick, hard deposit that can eventually clog the blood vessel and restrict the flow of oxygenated blood. This condition is termed atherosclerosis and can lead to heart attack or stroke.

High Density Lipoproteins (HDLs) on the other hand seem to do the opposite. They actually remove cholesterol from the artery walls and return it to the liver for disposal. It's not surprising therefore that LDL, which contributes significantly to hypercholesterolemia (high cholesterol) is widely dubbed the "bad" cholesterol and HDL the "good" cholesterol.

Coronary Heart Disease (CHD) is the biggest cause of death in the UK, taking one in five women and one in four men. There is a clear link between these horrifying statistics and the fact that the average blood cholesterol level in the UK is one of the highest in the world - 5.8mmol/litre compared to, say 4.2mmol/litre in China. What is even more surprising though is that every time our cholesterol level drops by 1%, our risk of heart disease falls by 2%. If this is the case, why aren't we all doing more to cut our own risk?

Perhaps the principal reason is that we don't even know we're at risk. Atherosclerosis remains an invisible problem until an affected artery becomes so clogged with sludgy cholesterol that heart attack or stroke occurs "out of the blue."

Another reason is that it is not obvious which foods contribute to raising blood cholesterol levels. Eggs, prawns, shrimps and organ meats like liver actually contain natural cholesterol and are best avoided if your cholesterol level is very high. However, if they are eaten, it is thought that the body simply compensates by producing less cholesterol in the liver. The real baddies in terms of cholesterol are saturated fats, the prime sources of which are dairy products, animal fats and tropical oils like palm and coconut. These all raise levels of LDL cholesterol, while polyunsaturated fats like vegetable oils lower both "good" and "bad" cholesterol and monounsaturated fats like olive oil reduce "bad" cholesterol and, at the same time help to protect levels of the "good" HDL cholesterol.

As well as restricting intake of the wrong types of fat, cholesterol levels can also be controlled by reducing its absorption in the gut. Fibre in fruit and vegetables helps to do this by speeding the passage of foods through the intestine but high amounts of fibre will reduce HDL as well as LDL cholesterol.

The most valuable dietary components for reducing cholesterol levels are plant sterols and plant stanols. Sterols are a natural part of the cell membrane in both plants and animals, cholesterol being exclusively an animal sterol. Plant stanols, less common in nature are produced by hydrogenating sterols and the term sterols is generally used as a generic term to encompass both. Because plant sterols are structurally very similar to cholesterol, they reduce the absorption of cholesterol by competing for the limited sites for take-up in the gut. The result is a lower concentration of cholesterol in the bloodstream.

Unfortunately, plant sterols are easily destroyed during food processing and, as a consequence, we generally don't consume anywhere near as many as we should. Studies indicate that consuming 2g per day of plant sterols can significantly reduce LDL cholesterol while retaining HDL levels and produce a 25% reduction in the risk of heart disease. The average daily intake in the UK is a pitiful 167mg.

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