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Department of Nutritional Sciences, Oklahoma State University, Stillwater, Oklahoma 74078
2To whom correspondence should be addressed at Department of Nutritional Sciences, 416 Human Environmental Sciences; Oklahoma State University, Stillwater, OK 74078. E-mail: arjmand{at}okstate.edu
Soy protein consumption has been linked to reduction in hypercholesterolemia, a risk for coronary heart disease. However, to what extent soy protein itself or its non-nutritive components, e.g., isoflavones and saponins, exert this cholesterol-lowering effect requires further investigation. To evaluate the effect of the protein component alone on lipid variables, ethanol-extracted, isoflavone-depleted soy protein isolate (SPe) was studied in ovarian hormone-deficient hamsters. Forty-eight 6-month-old female Golden Syrian hamsters were either sham-operated or ovariectomized and fed casein-based or SPe-based diets for 70 d. Ovariectomy, but not protein source, significantly (P < 0.05) increased serum phospholipids and total, nonhigh density lipoprotein, free and esterified cholesterol concentrations. Serum HDL cholesterol concentrations were not altered with either treatment. No significant differences were observed in liver total lipids or liver total cholesterol among the groups. Soy protein isolate, however, lowered serum triglyceride concentrations in both sham-operated and ovariectomized hamsters. These findings confirm the ovariectomized hamster as a model of postmenopausal hypercholesterolemia. The results are consistent with earlier observations that isoflavones or other nonprotein components, perhaps in combination with soy protein, play an important role in exerting this hypocholesterolemic effect. Further studies are needed to investigate whether isolated nonprotein components of soy would be able to prevent the ovarian hormone deficiencyassociated rise in serum cholesterol regardless of dietary protein source.
KEY WORDS: lipids triglycerides casein ovariectomy isoflavones
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