Women seeking an alternative to hormone-replacement therapy have hoped that soy foods, which contain a plant type of estrogen, might help prevent bone loss and lessen menopausal symptoms. But a major new clinical trial has found no benefit from soy compared to a placebo.
Part of the enthusiasm for soy stems from the lower prevalence of fractures from osteoporosis, as well as lower rates of breast cancer and cardiovascular disease, among women in Asia. Thats commonly been attributed to the high amounts of soy products in the typical Asian diet. But Silvina Levis, MD, of the University of Miami, and colleagues noted that previous research attempts to replicate such benefits in non-Asian populations using soy supplements were limited by short duration, small study population and poor design.
In their new Soy Phytoestrogens As Replacement Estrogen (SPARE) study, Dr. Levis and colleagues studied 248 women, ages 45-60, who were all within five years of the start of menopause. The women were randomly given either 200 milligrams daily of soy isoflavone tablets or a placebo.
After two years of followup, researchers found no significant difference in bone density at the lumbar spine, hip or femoral neck between those on soy supplements and those in the placebo group. Rather than seeing a benefit, women in the soy group actually suffered significantly more hot flashes.
In an accompanying editorial in Archives of Internal Medicine, Katherine Newton, PhD, of Group Health and Deborah Grady, MD, MPH, of the University of California-San Francisco, noted that soy may still have benefits for the fraction of women who can metabolize soy compounds into a more biologically active form. But they added that treatment may need to move away from the hope of a one-size-fits-all therapy for menopausal symptoms towards using existing treatments to target the symptoms that disturb patients most.
This is pretty convincing for soy, comments Bess Dawson-Hughes, MD, director of Tufts HNRCA Bone Metabolism Laboratory. However, it doesnt mean that all phytoestrogens are ineffective. More research is needed on the latter.
As for the lower incidence of osteoporosis among Asian women, other researchers whove failed to find bone benefits from soy have speculated that soy alone may not be responsible. Genetics as well as other dietary differences may contribute to Asian womens healthier bones.
TO LEARN MORE: Archives of Internal Medicine, August 8, 2011; abstract at archinte.ama-assn.org/cgi/content/abstract/171/15/1363.