Soy Doesn't Improve Bones in Young Women
Benefits May Be Confined to Those Who are Menopausal and Older
Oct. 25, 2002 -- Studies suggest that eating foods rich in soy helps protect older women from bone loss, but a new study finds that the same is not true for young women.
In a University of North Carolina (UNC) study, women in their 20s who ate diets high in isoflavone-enriched soy protein did not show improvements in bone mineral content and bone density. And women who consumed isoflavone-deficient diets saw no declines in bone density during the yearlong study.
The isoflavones found in soy are structurally similar to human estrogens, which are known to protect women against bone loss prior to and after menopause. Two recent short-term studies suggest that eating an isoflavone-rich diet may slow bone loss in women who are menopausal and beyond. In one of the studies, postmenopausal women eating high soy diets had modest improvements in spine bone density.
"Even though the women in our study were young, we were surprised to find no benefit in terms of bone health," lead researcher John J.B. Anderson, PhD, tells WebMD. "We aren't saying that isoflavones don't benefit these women in other ways. But they did not have a measurable impact on bone mineral density."
Anderson, who is a professor of nutrition at UNC's schools of public health and medicine, speculates that naturally occurring estrogens are so effective at protecting younger women against bone loss that they may overwhelm any possible effects conveyed by isoflavones.
He adds that the findings say nothing about the benefits of dietary soy in young girls who are approaching or have just reached puberty.
"We know that this is a critical time for bone building, and that at this age there are low levels of circulating estrogen," he says.
Anderson's study included 28 women in their 20s who either took a soy protein-diet enriched with isoflavones for a year or who consumed placebosupplements with no isoflavones. The researchers measured bone mineral content and density at the beginning of the study and at six months and one year.
They found no changes in bone density and content at the end of the study in either the isoflavone-treated women or the isoflavone-deficient group. The findings are reported in the October issue of the Journal of the American College of Nutrition.