Dietary equol induces changes in femur, but not tibia, calcium content of ovariectomized rats in a dose‐dependent manner

Abstract

Soy isoflavones and their metabolites have been considered strong candidates for reducing estrogen‐related bone loss. In particular, equol, a product of intestinal bacteria metabolism of the soy isoflavone, daidzein, shows potential, but less than 30% of the American population is capable of producing equol. Equol exhibits stronger estrogenic activity than daidzein. We examined the effect of (+/−)‐equol on calcium metabolism and bone parameters in ovariectomized (OVX) rats. We conducted an eight‐week feeding study and compared four dietary treatments of (+/−)‐equol (0, 50, 100, 200 ppm) in 6‐month old OVX female Sprague‐Dawley rats. SHAM rats (control group) and OVX rats on the highest amount of (+/−)‐equol had significantly higher calcium in the femur. All OVX rats receiving dietary (+/−)‐equol had significantly lower calcium in the tibia than SHAM and OVX control groups. There were no significant group differences in calcium balance, late in the intervention, over a period of 4 days. SHAM rats had significantly higher femur bone density than all OVX groups. There were no significant differences in bone length or width for right femurs or tibias. Thus, (+/−)‐equol increased calcium content and breaking force of a non‐loaded bone, but not a loaded bone, but only at the highest level, which also significantly increased uterine weight.