Promotion of bone growth by dietary soy protein isolate: Comparison with dietary casein, whey hydrolysate and rice protein isolate in growing female rats

Abstract

The effects of different dietary protein sources: casein (CAS), soy protein isolate (SPI), whey protein hydrolysate (WPH) and rice protein isolate (RPI) on bone were studied in intact growing female rats and in ovarectomized (OVX) rats showing sex steroid deficiency‐induced bone loss. In addition, SPI effects on bone were compared to those of 17β‐estradiol (E2) in the OVX osteopenic rat models. Peripheral quantitative computerized tomography of tibia demonstrated that SPI, WPH and RPI diets all had positive effects on either bone mineral density or content (BMD, BMC) relative to CAS, but SPI had the greatest effects in both intact and OVX female rats. Soy and E2 showed positive effects on BMD and BMC in OVX rats, respectively, but trabecular BMD was lower in SPI+E2 groups compared to E2 alone. E2 reduced both serum bone formation (osteocalcin, alkaline phosphotase) and resorption (RatLaps) markers. In contrast, SPI increased serum bone formation markers but suppressed bone resorption markers. Interestingly, both SPI and E2 increased alkaline phosphatase gene expression while SPI but not E2 decreased RANKL and estrogen receptor gene expression in RNA isolated from whole tibial bone. These data suggest that dietary protein source can affect bone quality and that beneficial SPI effects on bone are modulated by E2 status. Supported in part by ARS CRIS #6251‐51000‐005‐03S.