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May 14, 2010 | Comments: 0

Soybeans for Bones

Is soy beneficial for bones—especially for women after menopause, when bone loss accelerates? It’s too soon to say, but isoflavones in soy may help stimulate bone formation.  

Women in Asia, where soy foods are frequently consumed, have low rates of osteoporosis, compared to Western women, who eat little soy. Even among women in Asia, those with the highest soy intake tend to have higher bone density and fewer fractures. Such observations do not prove that soy is responsible for the bone protection, however. Other diet, lifestyle, or genetic factors may be responsible.  

Clinical trials, in which soy is added to people’s diets, have had mixed results. Most studies have involved postmenopausal women taking soy isoflavone supplements, not soy foods. An analysis of 10 studies in 2008 linked soy isoflavones to improved spinal bone density. But a more recent analysis concluded that isoflavones are unlikely to have a significant benefit on bone density at the hip or spine. A study in the American Journal of Clinical Nutrition in 2009 found that soy reduced whole-body bone loss but didn’t slow bone loss at sites where postmenopausal women are likely to have a fracture. No studies have looked at whether soy actually reduces fractures.

Not soy clear cut

Even if soy foods—and the isoflavones they contain, in particular—help keep bones strong, the effect is probably small. And not everyone may benefit. There is some evidence that people break down isoflavones into different active byproducts, and this can have varying effects on bone. It may also depend on when soy is consumed—that is, soy may lessen bone loss, or even help build bone, in women in the early years after menopause but have little or no effect later in life. Even less is known about soy’s effects in young women or in men. 

It’s also not clear which compounds in soy are most important, or how much you need to consume. Part of the proposed bone benefit may come from soy protein, which many  supplements lack. Moreover, the long-term safety of isoflavone supplements is largely untested, and researchers caution women with (or at high risk for) breast or endometrial cancer not to take them.

Words to the wise: Soy foods—such as tofu, soy milk, edamame, and tempeh—are worth eating, in moderation, if you like them. Even if their bone-health benefits are not confirmed, they provide good-quality protein and other nutrients, including magnesium, boron, and often calcium, which are important for bones and overall health. 

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