A SOY-PROTEIN-BASED DIET DOES NOT ALTER SERUM MARKERS OF BONE FORMATION AND RESORPTION IN OVARIECTOMIZED, LOW-FIT RATS

Matthew W. Richard, Laura C. Ortinau, Terese Z. Zidon, Pamela S. Hinton and Victoria Viera-Potter. University of Missouri, Columbia, MO; e-mail: [email protected] Osteoporosis and the associated increased risk of fracture are serious health concerns for postmenopausal women. In addition to a significant decline in estrogen post-menopause, decreased physical activity may further predispose women to osteoporosis. The soy isoflavones genistein and daidzein are phytoestrogens, and, therefore, might reduce the negative effects of estrogen loss on bone. Low-capacity runner (LCR) rats are selectively bred for intrinsically low aerobic fitness and might serve as an effective model of menopause, following ovariectomy. Purpose: Therefore, the purpose of this study was to examine the effects of a soy-protein-based diet or a corn-based-diet on serum bone markers of formation and resorption in ovariectomized, low-capacity runner (LCR) rats. Methods: LCR rats were either ovariectomized or sham operated and fed a soy-protein-based diet (600 ppm genistein+daidzein; SOY) or a corn-gluten-meal-based protein diet (\u3c15 ppm genistein+daidzein; CORN) for 23 weeks. Bone formation (osteocalcin, OC; propeptide type I procollagen, P1NP) and resorption (tartrate-resistant acid phosphatase, TRAP5b; C-terminal telopeptide of type I collagen, CTx) serum markers in LCR rats were measured following ovariectomy (OVX) or sham (SHAM) surgery at 28 weeks of age. Results: Final body weight was significantly increased by OVX vs. SHAM (p=0.002), but not by diet. P1NP, OC, TRAP5b, and CTx were measured in plasma using ELISAs. A two-factor (OVX, diet) ANOVA was used to test for significant main and interactive effects. There was a trend for OC and CTx to be higher and TRAP5b lower in OVX vs. SHAM (main effects: p=0.098, p=0.083, and p=0.099, respectively). In OVX, P1NP/CTx was significantly less than SHAM (p=0.003). Conclusion: There were no effects of diet on serum bone markers. In conclusion, serum markers of bone formation and resorption are affected by OVX, but not by a soy-protein-based diet, in LCR rats