Soy isoflavones do not affect bone resorption in postmenopausal women: A dose-response study using a novel approach with Ca-41

Published in:

Journal of Clinical Endocrinology and Metabolism 92,2 (2007) 577-582;


Introduction: The purpose of this 3-way crossover study was to identify the effective dose of soy protein isolate enriched with isoflavones for suppressing bone resorption in postmenopausal women using a novel, rapid assessment of antibone resorbing treatments. Methods: Thirteen postmenopausal women (>= 6 yr since menopause) were predosed with Ca-41 iv. After a 200-d baseline period, subjects were given 43 g soy protein/d that contained 0, 97.5, or 135.5 mg total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-d intervention phase was preceded by a 50-d pretreatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four-hour urine samples were collected approximately every 10 d during each phase for Ca-41/Ca analysis by accelerator mass spectrometry. Results: Serum isoflavone levels reflected the amount of isoflavones consumed in a dose-dependent manner. None of the isoflavone levels had a significant effect on biochemical markers of bone turnover, urinary cross-linked N teleopeptides of type I collagen and serum osteocalcin, or bone turnover as assessed by urinary Ca-41/Ca ratios. Conclusions: Soy protein with isoflavone doses of up to 135.5 mg/d did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary Ca-41 excretion from prelabeled bone.


randomized controlled-trial;; accelerator mass-spectrometry;; intestinal calcium-absorption;; mineral density;; biochemical markers;; protein isolate;; metabolism;; estrogen;; osteoporosis;; risedronate

Date of this Version

January 2007

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