EFFECTS OF CASEIN, SOY, AND WHEY PROTEINS AND AMINO-ACID SUPPLEMENTATION ON CHOLESTEROL-METABOLISM IN RATS

Cholesterol metabolism was studied in male rats fed high-fat, cholesterol-enriched diets containing casein, soy, or whey protein. Liver weight, total lipids, and cholesterol were higher for rats fed casein and whey than for those fed soy. Serum total, HDL, and LDL cholesterol were not significantly altered by the protein fed. VLDL cholesterol was lower for rats fed soy than for those fed casein, but there were no significant differences between whey-fed rats and the other two groups. During week 1, fecal output was highest for the soy-fed group, but during week 7, it was highest for the whey-fed group. During week 1, fecal cholesterol, coprostanol, and total steroids for the soy-fed group were higher than for the other two groups. During week 7, the soy-fed group was still excreting the most coprostanol, but the least cholesterol. Addition of amino acids had little impact on liver total lipids or cholesterol, except they decreased with addition of methionine to soy and whey diets. Serum total and LDL cholesterol were not altered by amino acid supplementation. Addition of cystine to casein decreased VLDL cholesterol. Addition of methionine to soy and whey increased HDL cholesterol. Little effect of amino acid supplementation was found on fecal steroids.