Satured fats and cholesterol

There are several potential mechanisms by which an intake of saturated fat could lead to increased blood cholesterol:
bullet unsaturated fatty acids tend to favour the formation of HDLs. Presumably this is linked to the reaction involving the enzyme lecithin cholesterol acyl transferase (LCAT) in which unsaturated fatty acids are transferred from plasma lecithin (a phospholipid) onto the cholesterol molecule to form an ester. HDL then transports this cholesterol to the liver where it is broken down. Hence unsaturated fatty acids would tend to reduce plasma cholesterol. Conversely saturated fatty acid or low levels of unsaturated fatty acid would elevate cholesterol levels in plasma because HDL levels relative to LDL have decreased.

Low-density lipoprotein (LDL) particles tend to contain cholesterol esters rich in saturated fatty acids, whereas high-density lipoprotein (HDL) contains unsaturated fatty acids. Thus a high proportion of saturated fatty acids in the diet could (in theory at least) increase LDLs

Saturated fatty acids and cholesterol tend to be present together in foods such as animal fat. Hence consumption of food rich in saturated fatty acids would raise cholesterol levels concurrently. (However, a recent study by Kromhaut (1999) indicates that this does not apply in the case of stearate which does not raise LDL)
Saturated fatty acids may have some regulatory effects on cholesterol synthesis which tends to raise plasma cholesterol levels (via LDL), an effect which is not produced by unsaturated fatty acid.

There is clear epidemiological evidence that diets rich in cholesterol and saturated fats lead to an increased risk of coronary heart disease as a consequence of high plasma cholesterol levels promoting the development of atherosclerotic plaques in blood vessel walls. Polyunsaturated fatty acids are regarded as being protective because they reduce the risk of atheroma development.

Saturated fats taken in with the diet are incorporated into cholesterol esters (and triglycerides) which form part of the LDL complexes in the blood, whereas polyunsaturated fatty acids are taken up mainly into cholesterol esters in HDL. The chemical composition of these two particles is quite different: LDL contains 80% fat, of which 50% is made up of cholesterol, and 20% protein. HDL contains 55% fat, of which 25% is cholesterol, and 45% read more