Effect of soy protein-containing isoflavones on lipoproteins in postmenopausal women.

OBJECTIVE: Some clinical trials have demonstrated a beneficial effect of dietary soy protein on improving lipoproteins. Research also has documented that serum lipoproteins and some lipoprotein subclasses are altered as a consequence of menopause, resulting in a more atherogenic lipid profile. The purpose of this study was to determine the effects of isolated soy protein-containing isoflavones on lipoproteins and lipoprotein subclasses in both African American and white postmenopausal women with borderline to moderate low-density lipoprotein cholesterol elevations.

DESIGN: This was a randomized, double-blind, controlled clinical trial including 216 postmenopausal women. After a 4-week run-in period with a casein protein-based supplement, participants were randomly assigned to continue the casein placebo or receive soy protein-containing isoflavones for a period of 12 weeks.

RESULTS: In the soy group, the total cholesterol, low-density lipoprotein cholesterol, and low-density lipoprotein particle number decreased significantly as compared with the placebo group at 6 weeks. Although this decrease continued at 12 weeks in the soy group, the difference from the placebo group was attenuated for total cholesterol and low-density lipoprotein particle number. Multivariate analyses controlling for age, race, change in weight, change in dietary fat intake, and change in kilocalorie energy expenditure revealed that treatment remained a significant independent predictor of change in total cholesterol (P = 0.01), low-density lipoprotein cholesterol (P = 0.02), and low-density lipoprotein particle number (P = 0.002) after 6 weeks of dietary soy.

CONCLUSIONS: Increased consumption of soy protein replacing animal protein that is high in fat may help improve atherogenic lipid profiles.