BOX2–3 LIPIDS IN THE BLOOD
cause in this form cholesterol is more easily
removed from the blood by the liver and excreted
in bile.
A diet low in total fat, with most of it unsaturated
fat, tends to raise HDL levels and lower LDL levels.
The benefit is the delaying of atherosclerosis and
coronary artery disease. A simple blood test called a
lipid profile (or lipid panel) can determine levels of
total cholesterol, triglycerides, HDLs, and LDLs. A
high HDL level, above 50 mg/dL, is considered
good, but some researchers now believe that the
LDL level is more important and should be as low as
possible, below 100 mg/dL.
Other factors contribute to coronary artery dis-
ease, such as heredity, smoking, being overweight,
and lack of exercise. Diet alone cannot prevent ath-
erosclerosis. However, a diet low in total fat and
high in polyunsaturated fats is a good start.Triglycerides and cholesterol are transported in the
blood in combination with proteins. Such mole-
cules made by the small intestine are called chy-
lomicrons. Those made by the liver are called
lipoproteins and are categorized by their density,
which reflects the proportion of protein to choles-
terol.
Low-density lipoproteins (LDLs, which are low in
protein and high in cholesterol) transport choles-
terol to the tissues, where it is used to synthesize
cell membranes or secretions. LDLs are also called
“bad cholesterol,” because in this form the choles-
terol is more likely to be deposited in the walls of
blood vessels, leading to atherosclerosis.
High-density lipoproteins (HDLs, which are
higher in protein and lower in cholesterol than
LDLs) transport cholesterol from the tissues to the
liver. HDLs are also called “good cholesterol,” be-BAGlycerol
Triglyceride
3 Fatty acids
Cholesterol
Figure 2–7. Lipids. (A) A triglyceride made of one glycerol and three fatty acids. (B) The
steroid cholesterol. The hexagons and pentagon represent rings of carbon and hydrogen.
QUESTION:What would a diglyceride look like?36