No positive effect on bone health from soy isoflavones seen in randomized trial

Researchers at the University California-Davis, Iowa State University and centers, who conducted the longest study of its kind into the role that soy isoflavones play in the health of postmenopausal women, found only a slight benefit when the target population used this natural compound, according to a United Stated Department of Agriculture-Research, Education, and Economics press release.

However, what Agricultural Research Service (ARS) physiologist Marta D. Van Loan and colleagues learned from their 3-year randomized, controlled study of estrogen-like soy isoflavones has helped shed light on the role that these natural compounds may play in strengthening the skeleton.

According to Van Loan, more than two dozen other studies have already been conducted in this area, since soy has potential as a possible substitute for conventional steroid hormone replacement therapy for postmenopausal women. Some of those investigations suggested that soy enhances bone health, she noted in the release.

Van Loan, who is with the ARS Western Human Nutrition Research Center at the University of California-Davis, teamed up with Iowa State University researcher D. Lee Alekel and others to determine whether isoflavones extracted from soy protein would protect postmenopausal volunteers against bone loss.

Study participants took either a placebo tablet or a tablet containing one of two moderate amounts of the isoflavones — 80 mg or 120 mg — for the duration of the investigation. According to the press release, the isoflavones had no significant positive effect on preventing bone loss. However, the 120-mg treatment showed a modest benefit when evaluated in conjunction with lifestyle factors.

The findings were reported in the American Journal of Clinical Nutrition.

Explaining their results, researchers theorized the body's response to isoflavones extracted from soy proteins may be different from responses to isoflavones in their natural matrix of soy protein or soy foods, or in a soy-protein supplement. Or, some soy-protein compound other than the extracted isoflavones may have been responsible for the bone-protecting effects seen in some previous studies. Finally, the isoflavone doses used in this study may not have been high enough to produce a bone-sparing effect, according to the release.

Reference:
Alekel DL, et al. Am J Clin Nutr. 2010 Jan;91(1):218-30.

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