Intact dietary soy protein, but not adding an isoflavone-rich soy extract to casein, improves plasma lipids in ovariectomized cynomolgus monkeys

The dietary consumption of soy protein has been linked to a reduction in co ronary heart disease and improvements in a number of related risk factors. Recent investigations have focused on isoflavone components of soy protein. The purpose of this study was to examine plasma lipids and lipoproteins, p articularly LDL, with the intake of intact soy protein or casein-lactalbumi n diets with and without a semipurified extract of soy, rich in isoflavones . Sixty ovariectomized cynomolgus monkeys were assigned to one of three gro ups fed diets containing the following: 1) casein-lactalbumin as the protei n source (CAS; n = 20); 2) CAS plus a semipurified extract of soy, rich in isoflavones (ISO; n = 20); or 3) intact soy protein (SOY; n = 20) for 12 wk . Lipoproteins were fractionated by combined ultracentrifugation and HPLC. Isolated LDL particles were further subfractionated by dividing the LDL pea k into three fractions for compositional analyses. The SOY group had signif icantly lower plasma total cholesterol, VLDL plus IDL cholesterol and LDL c holesterol, and significantly less HDL cholesterol than the CAS group. LDL particles from the SOY group had a significantly less cholesteryl ester tha n the CAS group. The semipurified extract of soy, rich in isoflavones, adde d to casein-lactalbumin protein did not have the same effects as intact soy protein on plasma lipids and lipoproteins, Other components of soy protein , either alone or in combination with isoflavones, may be involved in the e ffects seen in this study.