Effect of soy isoflavones and prebiotics on bone metabolism in a post menopausal rodent model
Post menopausal women are at increased risk for several chronic diseases, including osteoporosis and cardiovascular disease. Phytoestrogens, especially equol and genistein, and prebiotics are of interest for their potential to improve bone and heart health by increasing calcium retention and lowering cholesterol. There are limited data on the dietary effects of equol on bone and metabolism of dietary equol and its metabolites. A dose response study of equol at low (50 ppm), medium (100 ppm), and high (200 ppm) doses on bone properties and a pharmacokinetic study comparing dietary daidzein and equol were conducted in ovariectomized (OVX) Sprague Dawley rats. In OVX rats receiving 200 ppm equol, femoral calcium concentration was greater compared to lower doses but was still less than SHAM (p<0.05); other bone measures were not improved. At this dietary equol intake, uterine weight was significantly higher (p<0.05) than other OVX groups, but lower than the SHAM operated intact rats. At 200 ppm, dietary equol also significantly increased proliferative index in the uterine epithelium. Dietary equol had no stimulatory effect on mammary gland epithelium. The majority (≥99%) of circulating equol metabolites present were glucuronide conjugates. However, low levels of sulfated conjugates were detected, specifically equol monosulfate. There were higher and longer circulating equol sulfated conjugate concentrations with dietary equol compared to dietary daidzein. Another soy isoflavone, genistein, has also gained interest due to its potential bone and heart benefits. Recent evidence suggests a combination of prebiotics and phytoestrogen consumption may be more effective than either alone. A four week feeding study was conducted in 5 mo. old OVX Sprague Dawley rats to examine the effect of genistein, Synergy® (prebiotic) and genistein + Synergy® on bone density and strength, calcium metabolism and lipid biomarkers. SHAM Control rats had significantly higher femoral bone density, as determined by underwater weighing, than all other groups. A three-point bending test showed that OVX rats receiving daily estradiol injections, and OVX rats on 5% Synergy® diet matched bone breaking strength (p<0.05) of the SHAM Control. Rats receiving genistein only had significantly lower total cholesterol than Control, rats receiving daily estradiol injections, and rats fed 5% Synergy® . Dietary equol provided minimal bone health effects at a dose that caused adverse effects on reproductive tissue. Genistein supplementation imparted modest heart health benefits and prebiotic consumption (Synergy® ) resulted in mild bone health benefits in ovariectomized rats.
Weaver, Purdue University.
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