Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women

Background: No published studies have directly examined the effect of soy p rotein with isoflavones on bone or bone turnover in perimenopausal women. Objective: Our objective was to determine the effects of 24 wk of consumpti on of soy protein isolate with isoflavones (80.4 mg/d) in attenuating bone loss during the menopausal transition. Design: Perimenopausal subjects were randomly assigned, double blind, to tr eatment: isoflavone-rich soy (SPI+; n = 24), isoflavone-poor soy (SPI-; n = 24), or whey (control; n = 21) protein. At baseline and posttreatment, lum bar spine bone mineral density (BMD) and bone mineral content (BMC) were me asured by using dual-energy X-ray absorptiometry. At baseline, midtreatment , and posttreatment, urinary N-telopeptides and serum bone-specific alkalin e phosphatase (BAP) were measured. Results: The percentage change in lumbar spine BMD and BMC, respectively, d id not differ from zero in the SPI+ or SPI- groups, but loss occurred in th e control group (-1.28%, P = 0.0041; -1.73%, P = 0.0037). By regression ana lysis, SPI+ treatment had a positive effect on change in BMD (5.6%; P = 0.0 23) and BMC (10.1%; P = 0.0032). Baseline BMD and BMC (P less than or equal to 0.0001) negatively affected the percentage change in their respective m odels; baseline body weight (P = 0.0036) and bone-free lean weight (P = 0.0 16) contributed positively to percentage change in BMD and BMC, respectivel y. Serum BAP posttreatment was negatively related to percentage change in B MD (P = 0.0016) and BMC (P = 0.019). Contrast coding using analyses of cova riance with BMD or BMC as the outcome showed that isoflavones, not soy prot ein, exerted the effect. Conclusion: Soy isoflavones attenuated bone loss from the lumbar spine in p erimenopausal women.