In one trial, soy slowed bone loss overall and at no single site
Over two years, 403 postmenopausal women took 80 or 120 mg of soy isoflavones a day or placebo. Only the 120 mg arm separated, and only on whole-body density.
What the study found
Bone loss slowed across the whole body and nowhere in particular
Over two years, 403 postmenopausal women took 80 or 120 mg of soy isoflavones a day, or placebo, all of them with calcium and vitamin D. Only the 120 mg arm separated from placebo, and only on whole-body bone density: the hip, the spine and every other site measured showed nothing.
The caveat · How much bone was saved is unknown
The abstract gives p values and directions but no effect sizes, so how much bone was saved cannot be stated. Whole-body density is the weakest endpoint measured, and the sites where people actually fracture were null. The 80 mg arm showed nothing, so two doses do not make a dose-response.
What we don't know
The abstract gives p values and directions but no effect sizes, so how much bone was saved cannot be stated. Whole-body density is the weakest endpoint measured, and the sites where people actually fracture were null. The 80 mg arm showed nothing, so two doses do not make a dose-response.