A patient with familial type III hyperlipoproteinemia (HLP) was subjected to a clinical trial in which the effects of different diet regimens and drugs on all plasma lipoprotein density classes were studied. In this patient, whose plasma cholesterol and triglyceride were within normal limits under clofibrate treatment, medication was discontinued in favor of a diet enriched in carbohydrate. This management resulted, within eight days, in the development of a type III phenotype featuring all of the most widely used criteria typical for this form of lipid disorder. Very low density lipoproteins contained an increased amount of cholesterol and the "arginine-rich" apolipoprotein at both the beginning of the trial and at the eighth day. When the carbohydrate-enriched diet was replaced by a diet commonly used in type III hyperlipoproteinemia, the plasma cholesterol and triglyceride values were lowered to upper normal limits. However, after zonal ultracentrifugation, a lipoprotein profile typical for a type III subject without treatment was observed. Administration of either clofibrate or nicotinic acid to the type III diet resulted in a further decrease of the plasma levels of cholesterol and triglyceride. Zonal ultracentrifugation indicated that these decreases were caused by lowering the plasma concentrations of very low density, intermediate density, and low density lipoproteins. Furthermore, both drugs raised the two high density lipoprotein classes from their initially decreased levels to normal plasma values. These results suggest that drug and diet treatment of a type III hyperlipoproteinemic not only lowers the amount of very low, intermediate, and low density lipoproteins but also increases the high density lipoproteins which are considered protective against atherosclerosis.
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