Prevention of hypercholesterolemia in cholesterol-fed chickens by high-casein and high-soybean protein diets.

Chickens were fed cholesterol-enriched semipurified diets containing two levels (20% and 50%, w/w) of casein or soybean protein for 29 days. The ingestion of the cholesterol-enriched diets containing 20% casein or soybean protein resulted in markedly elevated levels of serum cholesterol, compared with the feeding of a cholesterol-free control diet containing 20% soybean protein. However, this hypercholesterolemic response could be prevented by feeding high-casein and high-soybean protein diets (50%). Similarly, lower levels of serum triglycerides and phospholipids were observed in the chickens fed the 50% protein diets compared with those fed the 20% protein diets. The excess of serum cholesterol and phospholipids in the 20% protein groups was mainly carried in the VLDL and to a lesser extent in the IDL fraction; this was associated with a decrease of cholesterol and phospholipids in the LDL fraction. The amount of cholesterol in the liver paralleled the cholesterol concentrations in the serum; the chickens fed the 20% protein diets exhibited significantly higher concentrations of liver cholesterol than those on the 50% protein diets. Thus, in chickens, the proportion of protein in the diet significantly affects the levels of serum and liver cholesterol, whereas there is practically no differential cholesterolemic effect of casein and soybean protein in the diet.