Brent Cornell

    
Humans can synthesise most fatty acids from carbohydrates, but two (cis)-polyunsaturated fatty acids are considered essential

• Alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) cannot be synthesised by the body
• This is because humans lack the enzyme required to introduce double bonds at the required position of the carbon chain

Essential fatty acids are modified by the body to make important lipid-based compounds (such as signalling molecules)

• There is evidence to suggest dietary deficiencies of these fatty acids may be linked to impaired brain development (e.g. depression) and altered maintenance of cardiac tissue (e.g. abnormal heart function) – although this evidence is contested

Foods rich in essential fatty acids (omega-3 and omega-6) include fish, leafy vegetables and walnuts

    
Fats and cholesterol cannot dissolve in the bloodstream and so are packaged with proteins (to form lipoproteins) for transport

• Low density lipoproteins (LDLs) carry cholesterol from the liver to the body (hence raise blood cholesterol levels)
• High density lipoproteins (HDLs) carry excess cholesterol back to the liver for disposal (hence lower blood cholesterol levels)

The mix of fatty acids consumed as part of a diet directly influences the levels of cholesterol in the bloodstream:

• Saturated fats increase LDL levels within the body, raising blood cholesterol levels 
• Trans fats increase LDL levels and lower HDL levels, significantly raising blood cholesterol levels
• Cis-polyunsaturated fats raise HDL levels, lowering blood cholesterol levels
  

High cholesterol levels in the bloodstream lead to the hardening and narrowing of arteries (atherosclerosis)

• When there are high levels of LDL in the bloodstream, the LDL particles will form deposits in the walls of the arteries
• The accumulation of fat within the arterial wall leads to the development of plaques which restrict blood flow
• If coronary arteries become blocked, coronary heart disease (CHD) will result – this includes heart attacks and strokes

Role of Cholesterol and Lipoproteins in Coronary Heart Disease