Soy Isoflavones Clinical Study

Cheong JM, Martin BR, Jackson GS, Elmore D, McCabe GP, Nolan JR, Barnes S, Peacock M, Weaver CM.

Foods and Nutrition, Statistics, PRIME Lab, Purdue University, West Lafayette, IN, USA, Pharmacology, University of Alabama, Birmingham, AL, USA, School of Medicine, Indiana University, Indianapolis, IN, USA.

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 anti-bone resorbing treatments.

Methods:
Thirteen postmenopausal women (>/= 6 yr since menopause) were pre-dosed with (41)Ca intravenously. After a 200-day baseline period, subjects were given 43 grams of soy protein per day that contained 0, 97.5, or 135.5 mg of total isoflavones in randomized order. The soy protein isolate powder was incorporated into baked products and beverages. Each 50-day intervention phase was preceded by a 50-day pre-treatment phase for comparison. Serum isoflavone levels and biochemical markers were measured at the end of each phase. Twenty-four hour urine samples were collected every approximately 10 days during each phase for (41)Ca/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 (NTx) and serum osteocalcin (OC), or bone turnover as assessed by urinary (41)Ca/Ca ratios.

Conclusions:
Soy protein with isoflavone doses of up to 135.5 mg per day did not suppress bone resorption in postmenopausal women. This is the first efficacy trial using the novel technique of urinary (41)Ca excretion from prelabeled bone.

PMID: 17148567 [PubMed - as supplied by publisher]

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