Effect of Soy Protein with Isoflavones on Postmenopausal Women

No beneficial effects were found on cognitive function, bone mineral density or plasma lipids when postmenopausal women age 60 years or older took soy protein supplements with isoflavones for one year, according to a study in the July 7 issue of The Journal of the American Medical Association (JAMA).

“The sudden decline in estrogen levels after menopause coincides with acceleration of several aging processes,” according to background information in the article. “On average, bone mineral density (BMD) decreases and cognitive function declines, whereas total cholesterol and low-density lipoprotein cholesterol (LDL-C) [the bad type of cholesterol] increase.” The authors write that some women have taken hormone therapy to counteract some of these changes; however, hormone therapy has short- and long-term risks. Isoflavones, estrogenlike compounds naturally occurring in plant foods, have been suggested as an alternative for traditional estrogen therapy with fewer adverse effects.

Sanne Kreijkamp-Kaspers, M.D., Ph.D., from the University Medical Center, Utrecht, the Netherlands, and colleagues conducted a study with 202 healthy postmenopausal women aged 60 to 75 years between April 2000 and September 2001 in the Netherlands. The women were randomly assigned to receive 25.6 grams of soy protein containing 99 milligrams (mg) of isoflavones or the placebo, a total milk protein as a powder, each of which could be mixed with food or beverages on a daily basis for 12 months. Cognitive testing was performed at baseline and at the final visit, one year later, using several standardized tests. Bone mineral density was measured at baseline and 12 months using dual-energy x-ray absorptiometry (DXA) scans, and plasma lipid levels also were assessed at baseline and 12 months.

“In this longer-term, relatively large double-blind, placebo-controlled , randomized trial, we did not find any effect of soy protein supplementation, which naturally contains large amounts of isoflavones, on cognitive function, BMD, or plasma lipids in the relevant population of aging women,” the authors report. Timing of the supplementation may provide an explanation for the difference in findings from this study compared to previous ones that were more promising, the authors write. “…the most pronounced effects of estrogen on cognitive function have been reported in perimenopausal women, and not in late postmenopausal women. With respect to bone, it has been suggested that it is easier to prevent changes or losses after menopause than reverse them when they have already taken place. … The influence of the timing of supplementation needs to be elucidated in further research,” the authors suggest.