Long‐Term Feeding of a Soy‐Protein‐Based Diet Improves Trabecular and Cortical Bone Outcomes in Low‐Fit, Intact and Ovariectomized Female Rats
Authors: Richard Matthew W. , Ortinau Laura C. , Zidon Terese M. , Hinton Pamela S , Vieira‐Potter Victoria 
Published: November 2023

Osteoporosis and related fractures are serious health concerns for postmenopausal women. In addition to the loss of estrogen, decreased physical activity may further predispose postmenopausal women to osteoporosis. Soy protein contains the phytoestrogens genistein and daidzein, which might reduce the negative effects of estrogen loss on bone. The objective of this study was to evaluate the effects of ovariectomy (OVX) and a soy‐protein‐based diet (SOY) on bone outcomes in female, low‐capacity‐running (LCR) rats selectively bred for intrinsically low aerobic fitness as a rodent model of menopause. Twenty‐eight week‐old LCR rats underwent OVX or sham (SHAM) surgery followed by 23 weeks of the SOY diet (600 ppm genistein+daidzein) or a corn‐gluten‐meal‐based protein diet (CORN, <15 ppm genistein+daidzein). At 52 weeks of age, body composition was measured using EchoMRI, and the animals were sacrificed and blood and tibiae collected. Glucose, insulin and triglycerides were measured in fasting plasma by a commercial laboratory. Serum markers of bone formation (osteocalcin, OC; propeptide type I procollagen, P1NP) and resorption (tartrate‐resistant acid phosphatase, TRAP5b; C‐terminal telopeptide of type I collagen, CTx) were measured using ELISA. Trabecular and cortical microarchitecture of the tibia were evaluated using μCT; torsional loading of the tibia to failure was used to assess cortical bone strength. A two‐factor (OVX, SOY) ANOVA was used to test for significant main and interactive effects with body weight as a covariate for extrinsic bone strength. Final body weight, body fat (%), and insulin were significantly increased by OVX vs. SHAM; uterine weight was significantly decreased by OVX vs. SHAM. There was a trend for OC and CTx to be higher and TRAP5b lower in OVX vs. SHAM (main effects: p<0.1). In OVX, the ratio of P1NP/CTx was significantly less than SHAM. There were no effects of SOY on serum bone turnover markers. OVX adversely affected trabecular microarchitecture; and SOY partially corrected the elevated trabecular spacing (Tb.Sp) and loss of connectivity density (Conn.D). SOY also improved Tb.Sp and Conn.D in SHAM rats. There were no effects of OVX or SOY on cortical thickness or relative area in the tibia. SOY significantly increased cortical strength outcomes (maximal torque, Tmax; torsional stiffness, Ks; and shear modulus of elasticity, G) independent of OVX. In conclusion, OVX adversely affected trabecular bone microarchitecture, and SOY partially attenuated loss of connectivity density and reduced increases in Tb.Sp. SOY also improved trabecular microarchitecture in ovary‐intact animals. SOY improved cortical bone strength in both intact and ovariectomized rats. Taken together, these results indicated that a soy‐protein‐based diet may improve trabecular microarchitecture and cortical bone strength in female low‐fit rats, regardless of ovarian hormone status.Support or Funding Information(The University of Missouri‐Columbia Center for Botanical Interactive Studies to V. Vieira‐Potter) by Grant Number P50AT006273; Department of Nutrition & Exercise Physiology.