Several clinical studies have examined the effect of soy protein and soy-derived isoflavones in the context of the prevention of cardiovascular disease (CVD). In a study in the American Journal of Clinical Nutrition, Gardner et al. studied soy protein with or without soy isoflavones to determine if the lipid-lowering effect of soy could be specifically attributed to the isoflavone-containing fraction. Soy consumption in the two groups was compared to a control group who consumed milk protein. The reduction in low-density lipoprotein (LDL) and cholesterol was greatest among those who consumed soy protein with isoflavones. However, an unexpected and similar LDL cholesterol reduction in the milk protein (control) group suggested that the reductions attributed to soy isoflavones may be non-specific.
The 94 postmenopausal women who participated in the study were healthy nonsmokers who had not been taking hormone replacements or lipid-lowering medications. During a dietary adaptation period, they consumed a milk protein supplement while reducing their consumption of other sources of calories and protein to maintain weight stability. Subsequently, they were randomly assigned to receive 42 grams daily of milk protein or soy protein that was either supplemented or unsupplemented with isoflavones. After 12 weeks, LDL cholesterol was reduced in both the control milk protein group and in the soy isoflavone group, but not in the plain soy protein group. HDL cholesterol and triacylglycerol concentrations did not change significantly in any of the study groups.
An accompanying editorial by Dr. Alice Lichtenstein reviews the varying results of soy isoflavone research to date. She concludes that soy protein enriched with isoflavones probably has a modest LDL-cholesterol lowering effect in persons in the high-risk range. Nevertheless, other unrealized diet and lifestyle goals, such as reduced body weight and intake of saturated fat, should remain primary targets in reduc
Contact: Elizabeth Horowitz
American Journal of Clinical Nutrition