If patients with hyperlipoproteinemia type IIa are treated with diet and 
additionally over a period of two weeks with 2 grams of Clofibrate daily, the 
cholesterol-level in the serum decreases. This decrease is caused mainly by a 
reduction of the apolipoprotein B and the LDL-cholesterol in serum. If elevated 
cholesterol-levels in the serum are reduced through a "prudent" diet, the 
concentration of apolipoprotein B in serum remains the same. It is not fully 
understood which influence a diet, which is rich in poly-unsaturated fatty acids 
and has a low content of saturated fatty acids and carbohydrates, has upon the 
lipoproteins in the serum. The mode of action of this diet and its significance 
for the concentration of HDL need further investigation.