Soy isoflavones do not affect bone resorption in postmenopausal women: a dose-response study using a novel approach with 41Ca.
BACKGROUND
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 (>or=6 yr since menopause) were predosed with 41Ca 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 41Ca/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 41Ca/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 41Ca excretion from prelabeled bone.
Cheong
J M K
JM
Foods and Nutrition, Purdue University, 700 West State Street, West Lafayette, Indiana 47907-2059, USA.
Martin
B R
BR
Jackson
G S
GS
Elmore
D
D
McCabe
G P
GP
Nolan
J R
JR
Barnes
S
S
Peacock
M
M
Weaver
C M
CM
D000328:Adult; D001862:Bone Resorption / Q000188:drug therapy* / Q000378:metabolism*; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000652:urine; D002132:Calcium Radioisotopes / Q000652:urine; D024042:Collagen Type I / Q000652:urine; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage*; D008875:Middle Aged; D015675:Osteocalcin / Q000652:urine; D010455:Peptides / Q000652:urine; D008517:Phytotherapy; D017698:Postmenopause; D030262:Soybean Proteins / Q000008:administration & dosage*
D002132:Calcium Radioisotopes; D024042:Collagen Type I; D007529:Isoflavones; D010455:Peptides; D030262:Soybean Proteins; C052929:collagen type I trimeric cross-linked peptide; D015675:Osteocalcin; D002118:Calcium