Objective:: This double-blind, 15-month pilot study was designed to investigate the effect of soy protein isolate with varying concentrations of isoflavones on early postmenopausal bone loss and lipids.
Design:: A total of 65 women, with a mean age of 55 years and 7.5 years since menopause, were randomized to one of three groups; soy protein with 96 mg isoflavones/day, soy with 52 mg isoflavones/day, or soy without isoflavones (< 4 mg isoflavones/day). Soy was given for 9 months and then discontinued; participants were followed for an additional 6 months. Bone mineral density (BMD) and blood lipids were measured during this time.
Results:: Measurement of serum isoflavones at 3 months showed dose-related increases in the three groups. There was no significant effect of the soy supplements on BMD of the spine or femoral neck in any of the three groups. BMD increased significantly in the trochanter at 9 months (P = 0.0219) and at 15 months (P < 0.05) in the group given isoflavone-free soy compared with the other two groups. There was no significant effect of soy on lipid metabolism at the end of the intervention.
Conclusion:: The present study did not find a significant positive effect of soy protein isolate supplemented with isoflavones on BMD and the serum lipid profile in early postmenopausal women.
Isoflavone supplemented soy protein isolate did not reduce bone loss at the spine or femoral neck in early postmenopausal women. There was no effect on bone markers, nor was there any positive effect on serum lipids.
From the 1Bone Metabolism Unit, School of Medicine and the 2Osteoporosis Research Center, Creighton University, Omaha, NE; and the 3Department of Pediatrics, University of Nebraska Medical Center, Omaha, NE.
Received April 9, 2003; revised and accepted August 29, 2003.
Part of this study was presented as an abstract at the 3rd International Symposium on the Role of Soy, October 1999, Washington, DC, USA (Gallagher et al, J Nutr 2000;130:666S–679S).
This work was supported by the Solae Company (St. Louis, MO) and the Nebraska Soy Bean Board.
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