Effects of dietary proteins from a variety of sources on plasma lipids and lipoproteins of rats.

Five experiments were conducted to study the effect of various protein sources on fasting blood lipids and lipoproteins in the rat. Plasma levels of total cholesterol, high density lipoprotein (HDL)-cholesterol and total triglyceride, as well as weight gain, food intake protein efficiency ratio and net protein utilization were measured over 28-day test periods with male Sprague-Dawley rats. The purified proteins studied included casein, egg albumin, lactalbumin, soy and alfalfa. Crude proteins studied included yeast, fish meal and blood meal. Diets low in methionine were supplemented with this amino acid to insure that all diets were nutritionally adequate. Although the plasma total cholesterol levels varied by 40-50% and HDL-cholesterol by 90% among the various diets, the changes were not associated with any particular dietary protein source or level. Plasma total triglyceride levels varied independently of the dietary source and level of protein. Plasma HDL-cholesterol accounted for approximately 70% of the plasma total cholesterol. Plasma HDL-cholesterol concentrations correlated positively (R = 0.72) with plasma total cholesterol and negatively (R = -0.34) with plasma triglyceride levels. These results clearly show that the pure and crude plant proteins did not have a hypocholesterolemic effect compared with pure and crude animal proteins in rats. Plasma HDL-cholesterol levels were the same in rats fed plant and animal proteins.