The Effect Of A Soybean Diet On Osteoporosis

Osteoporosis is a degenerative thinning of the bones related to decreasing estrogen levels. Soybeans and soy products have generated interest in connection with osteoporosis because they contain a phytoestrogen called isoflavone, which is believed to have potential as a substitute for estrogen without its adverse side effects. Unfortunately, although a few studies have shown improvements in bone health, more comprehensive studies have found no beneficial effects of either dietary soy consumption or soy supplements.

Osteoporosis and Estrogen

Osteoporosis is a weakening of the bones associated with decreasing estrogen levels. Although a small percent of persons suffering from osteoporosis are male, it is overwhelmingly a disease of postmenopausal women.

Until 2002, the standard of care for promoting post menopausal bone health was hormone replacement therapy, or HRT. That year, preliminary findings from the Women's Health Initiative, a large clinical trial, found that HRT reduced osteoporosis-linked fractures by 34 percent. However, other results of the Women's Health Initiative showed an increased risk of breast cancer with HRT. As a result, millions of women have stopped taking HRT and sought other alternatives to promote bone health.

What Is In Soy?

According to the Linus Pauling Institute of Oregon State University, soybeans and other soy products contain the richest dietary source of isoflavones. These phytoestrogens, plant products with estrogen-like properties, bind to estrogen receptors on cells throughout the body including bone tissue. It may vary with the type of tissue as to whether this binding to estrogen receptors blocks the binding of human estrogen or exerts weak estrogen-like responses.

For estrogen-sensitive tumors like breast cancer, blocking the action of human estrogen may reduce the risk. In contrast, the Linus Pauling Institute notes evidence that consuming soy isoflavones, instead of the estrogens in HRT, can stimulate positive effects on post-menopausal bone health while simultaneously generating the negative effects of increasing breast cancer risk.

The Research Question

Research on preventing osteoporosis looks at two measures. First, is a whether a particular treatment increases bone mineral density, or BMD. In osteoporosis, BMD decreases, thinning the bones making them subject to fracture. Second, is evidence that new bone is forming. We know that estrogen does both. The question is whether soy products can mimic these effects.

The Research Results

According to Harvard Health Publications, a 2009 clinical trial looked at the effects of both soy isoflavones and soy protein in postmenopausal women over a two-year period. The researchers concluded that neither the soy protein nor the isoflavone supplements built bone or prevented bone loss in postmenopausal women.

Another, larger study reported in 2010 reached the same conclusions. According to that report in the "Journal of Clinical Nutrition," researchers undertook a large, multisite, three-year study of women taking isoflavone tablets as a follow-up to their previous, smaller study that showed modest improvements in bone health. To their surprise, their second study, the longest and most comprehensive on the effects of soy isoflavones on bone density ever done, failed to show any improvement in bone mineral density or bone turnover.

Considerations

Although some studies have shown benefits to bone health in taking some form of soy products, the jury is still out. Most research has involved postmenopausal women, and little is known about whether consuming soy products prior to menopause might have an impact. Also, for research purposes, concentrated forms of soy isoflavones are usually used to promote consistency. It is not known whether consuming soy products such as soybeans in your diet would have the same effect. It is notable, however, that the National Osteoporosis Foundation does not discuss soy or soy isoflavones on its Web site. The only mention is in an article on diet and osteoporosis that states that soy milk might be fortified with vitamin D and calcium.