Time course of the development of hypercholesterolemia in rabbits fed semipurified diets containing casein or soybean protein

The time course of the development of hypercholesterolemia was studied in rabbits fed semipurified diets containing casein or soybean protein. When the rabbits were transferred from a commercial diet to semipurified diets, a rapid increase in the concentration of serum cholesterol and phospholipids occurred. After only one day on the semipurified diets, the cholesterol and phospholipid levels increased by about 50% on the diet containing soybean protein and more than doubled on the diet containing casein. Further elevations were observed after one and two weeks on the diets. However after one month, a decrease in the group on the diet containing soybean protein was found. The increases in serum cholesterol and the differences between the soybean protein and casein group were mainly attributable to differences in the LDL fraction and to a minor extent to differences in the HDL fraction. The feeding of semipurified diets resulted in a steep increase in the ratio of cholesterol to protein in all the lipoprotein fractions after only one day. This suggests that lipoprotein particles relatively rich in cholesterol were formed. Marked variations in the density profile of the serum lipoproteins were observed between individual rabbits fed semipurified diets.