Soy compounds help preserve bone.

Soy protein may have benefits that extend beyond those already known--reducing a person's risk of heart disease and of breast cancer. A pair of animal studies now suggests that soy also helps prevent the bone loss that can lead to osteoporosis and fractures in the elderly.

After menopause, women produce less estrogen, a hormone that helps keep bones strong. To simulate menopause in rodents, Bahrain H. Arjmandi of Oklahoma State University in Stillwater and his colleagues removed the ovaries of female rats. They then fed the animals diets rich in a protein from milk or soy.

Arjmandi's team found that accelerated bone turnover--breakdown and reformation--followed the simulated menopause. However, only among animals on the soy diets did the rate of bone formation exceed the rate of breakdown.

In a 9-week feeding trial, this net increase in the production of bone was small, the group reports in the December 1998 supplement of the AMERICAN JOURNAL OF CLINICAL NUTRITION. This suggests, the researchers say, "that for soy protein to reverse bone loss, long-term consumption may be necessary."

Findings from a 5-week feeding study, also reported in the issue, indicate that estrogenlike compounds in soy--principally the isoflavones daidzein and genistein (SN: 5/30/98, p. 348)--"are responsible for its bone-sparing effects." How the compounds spur bone growth remains unclear, Arjmandi's team adds.

The researchers say their data indicate that soy probably won't make a good substitute for estrogen-replacement therapy for bone protection, though it may offer a good adjunct.