Cholesterol is transported in the blood in complexes called lipoproteins. High-density lipoproteins (HDLs) tend to remove cholesterol from the tissues to the liver for excretion. Low-density lipoproteins (LDLs) are more likely to deposit cholesterol in damaged areas of blood vessels and lead to the formation of atherosclerotic plaques. High levels of LDL cholesterol can lead to heart disease, whereas high levels of HDL cholesterol can protect against heart disease.

Close-up on cholesterol

Cholesterol molecule diagram

Close-up on cholesterol

Cholesterol is a necessary part of all of us

Our notion of cholesterol as bad is overly simplistic. For example, it helps regulate the fluidity of cell membranes. And, in the context of health, often when we say ‘cholesterol’, we’re actually referring to two cholesterol transporters found in the blood: high-density and low-density lipoprotein, otherwise known as HDL (‘good’) and LDL (‘bad’) cholesterol. (For more, see our animation on cholesterol transport.)

While further subdivisions of LDL cholesterol do make the picture more complex, raised levels of LDL cholesterol are generally associated with an increased risk of heart disease.

According to most sources, it is not eating high-cholesterol foods, such as eggs, that drives up our blood cholesterol levels, but eating foods that are high in saturated fats. This is because our livers turn saturated fats like those in cakes and pastries into LDL cholesterol in the blood.

The past few years have seen continued questioning of dietary guidance on saturated fats and cholesterol. However, a 2015 study based on changing the diets of 195 people for 16 weeks showed that replacing saturated fats with unsaturated fats reduced LDL cholesterol levels.

Our cholesterol levels are not determined only by what we eat but also by the genes we inherit from our parents. About 1 in 500 people have an inherited condition called familial hypercholesterolaemia, which means they have high cholesterol from birth – whereas in 499 out of 500 people, cholesterol levels don’t get higher until they get older.

Lead image:

Cholesterol molecule diagram.

‘Big Picture: Fat’ (2015)


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About this resource

This resource was first published in ‘Fat’ in December 2015.

Cell biology, Health, infection and disease
Education levels:
16–19, Continuing professional development