Cholestrol

It is estimated that in the UK 45% of deaths from coronary heart disease in men and 47% iof deaths from coronary heart disease in women are due to a raise blood cholesterol level. It is thought that 10% of deaths from coronary heart disease in the UK could be avoided if everyone had a blood cholesterol level of less than 6.5 nmol/l. 

Like all lipids, cholestrol is not solube in water. In order to be transported in the bloodstream, insoluble cholesterol is combined with proteins to form soluble lipoproteins.

There are two major transport lipoproteins:

• low-density lipoproteins (LDLs) - the main cholesterol carrier in the blood. The triglycerides from saturated fats in our diet combine with cholestrol and protein to form LDLs. These circulate in the bloodstream and bind to receptor sites on cell membranes before being taking up by the cells. Excess LDLs in the diet overload these membrane receptors, resulting in high blood cholesterol levels. Saturated fats may also reduce the activity of LDL receptors so the LDLs are not rememoved from the blood, thus further increasing the blood cholesterol levels. This cholesterol may be deposited in the artery walls forming atheromas. 

• high-density lipoproteins (HDLs) - HDLs have higher percentage of protein compared with LDLs, hence their higher density. High-density lipoproteins are made with trigylcerides from unsaturated fats combine with cholesterol and protein. HDLs tranport cholesterol from the body tissues to the liver where it is broken down. This lowers blood cholesterol levels and helps remove the fatty plaques of atherosclerosis.

Monounsaturated fats are thought to help in the removal of LDLs from the blood. Polyunsaturated fats are thought to increase the activity of LDL receptor sites so the LDLs are actively removed from the blood.

LDLs are associated with the formation of atherosclerotic plaques whereas HDLs reduce the blood cholesterol deposistion. Therefore, it is desirable to maintain a higher level of HDL (good cholesterol) and a lower level of LDL (bad cholesterol). Eating a low-fat diet which particulary avoids saturated fats will help reduce total blood cholesterol, and especially LDL cholesterol, which constitutes the major component ofthe cholestrol risk for CVD.