Isoflavone-rich soy products may prevent bone loss in women

August 27, 2000

During the perimenopausal transition period, the average woman may be expected to lose 2-3% of bone per year, a deterioration which may continue into menopause leading to osteoporosis and possible bone fracture in later life. Current prevention includes hormone replacement therapy (HRT), but some women elect not to take this because of possible undesirable side effects. In a study by Alekel et al. published in The American Journal of Clinical Nutrition, consumption of soy protein powder with high levels of isoflavones appeared to lessen bone loss in the lumbar spine area in perimenopausal women who were not taking HRT. Soy-based foods may provide an alternative or adjunct treatment for women at this stage of life who are poor candidates for HRT or who choose not to receive it.

The double-blind study was conducted over a six month period using 69 white subjects who averaged 50.2 years of age, were going through the perimenopausal transition, and were not receiving HRT. The three treatment groups all consumed 40 grams of protein per day in the form of a jumbo muffin plus protein powder, one group receiving isoflavone-rich soy (SP+), one receiving isoflavone-poor soy (SP-), and one receiving whey control. The women's bone mineral density (BMD), bone mineral content (BMC) and serum bone-specific alkaline phosphatase (BAP)-an indicator of bone turnover-were measured at three time points during the study. Analysis of the lumbar spine at vertebrae L1-L4 was conducted using dual energy X-ray absorptiometry. Results indicated that the SP+ treatment attenuated bone loss from the lumbar spine, whereas the SP- and the control treatments had no effect on bone loss. At the conclusion of the study the control group had 1.08% lower BMD and 2.35% lower BMC than the SP+ group.

Preliminary studies in animals suggest that isoflavones exert both mild estrogenic and antiestrogenic effects, depending on the tissue in which they act. They may function as weak antagonists on the estrogen receptor, having an antiestrogenic effect in uterine and breast tissue. Alternatively, they may combine with the estrogen receptor in tissues with less estrogenic activity such as bone and blood vessel. In the current study, the SP+ treatment positively affected BMD and BMC, but showed no influence on changes in bone resorption and formation, which are an integral part of the menopausal transition. The fact that soy had a bone-sparing effect in the lumbar spine, but did not influence bone turnover suggests that it acts in a way that may be different from estrogen or other agents currently used as treatments for osteoporosis. Additional perceived health benefits of the regular consumption of soy, such as reductions in the incidence of cancer and heart disease in some populations might increase compliance in its use by perimenopausal women as an alternative to HRT in preventing bone loss. The authors add that, "This attentuation of loss, particularly if continued throughout the postmenopausal period, could translate into a decrease in lifetime risk of osteoporosis."

An editorial by Erdman et al. points out that 24 weeks is a short time period for a dietary study of bone loss because the bone remodeling cycle ranges up to 80 weeks. Although it would be premature to assume that soy isoflavones have a long-term bone-sparing effect, the positive results of two 24-week studies thus far underline the necessity for a longer period of study to confirm soy's benefits to bone.
-end-
Alekel, D Lee et al. Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. Am J Clin Nut 2000;72:844-852.

Erdman, John W et al Provocative relation between soy and bone maintenance. Am J Clin Nut 2000;72.

For more information please contact Dr. D L Alekel at alekel@iastate.edu or Dr John Erdman at j-erdman@uiuc.edu

This media release is provided by The American Society for Clinical Nutrition, to provide current information on nutrition-related research. This information should not be construed as medical advice. If you have a medical concern, consult your doctor.

To see the complete text of this article, please go to: http://www.faseb.org/ascn/temp/ajcn/September/844-852-alekel.pdf

American Journal of Clinical Nutrition

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