THE EFFECT OF DIETARY CASEIN AND SOYBEAN PROTEIN ON PLASMA-LIPID LEVELS IN CEBUS MONKEYS FED CHOLESTEROL-FREE OR CHOLESTEROL-ENRICHED SEMIPURIFIED DIETS

Two groups of six cebus monkeys were alternately fed semipurified diets containing either casein or soybean protein for periods of 8-10 weeks. The type of protein in the diet had little effect on the plasma cholesterol levels when cholesterol-free diets were fed. However, when 0.2% cholesterol was added to the diets, transferring the monkeys from a soybean protein diet to a casein diet resulted in a significant increase in plasma cholesterol levels (7.97 +/- 1.09 versus 9.33 +/- 1.31 mmol/L, n = 6, mean +/- SD). On the other hand, changing the monkeys from a casein diet to a soybean protein diet significantly lowered the plasma cholesterol levels (9.64 +/- 0.58 versus 7.41 +/- 1.07 mmol/L, n = 6, mean +/- SD). These changes in plasma cholesterol concentrations were attributed to changes in very-low and low-density lipoprotein cholesterol concentrations. The results of his study suggest that the different cholesterolemic effect of dietary casein and soybean protein in cebus monkeys becomes more pronounced when cholesterol-enriched diets are fed.