Women and Bone Health

Asian women have lower rates of hip fractures ¹ in spite of the fact that they consume less calcium and use hormone replacement therapy less frequently than Western women. This observation led researchers to investigate the possible role of soy protein and isoflavone consumption, which is significantly higher in the traditional Asian diet, in reducing the risk of osteoporosis.

A study of 24 403 postmenopausal women from Shanghai, followed for 4.5 years, showed a significant reduction in the risk of bone fractures (up to 37 %) with increasing soy food intake, especially in the early years following menopause ¹⁸ . However, clinical trials are necessary to confirm it is the soy providing the positive effect on bone, as population studies can only show associations but are unable to prove cause and effect. Various studies have therefore examined the effects of soy consumption on markers of bone turnover and bone mineral density.

Women consuming soy foods (as soy drink and soy nuts) for three months experienced an improvement in markers of their bone health. Specifically, consuming the soy diet was found to result in a drop in the level of a chemical marker of bone breakdown and an increase in the level of a protein indicating that the bone-making cells of the body were more active ¹⁹ . From a pool of 31 similar studies, looking at the effect of soy on markers of bone formation and bone breakdown, nine of the best designed were included in a meta-analysis that examined the effect of consuming soy isoflavones on a collective group of 432 subjects. The scientists from Peking University, Beijing, found that isoflavones - even at doses lower than 90 mg per day and taken for under 12 weeks - significantly inhibit bone breakdown and stimulate bone formation in menopausal women ²⁰ .

In the short-term Australian study by Dr. Fabian Dalais ⁸ discussed above, post-menopausal women consuming 45g of soy grits daily, experienced a surprising 5.2% increase in bone mineral content (BMC) after 12 weeks. Dr. Sue Potter, then from the University of Illinois ²¹ , reported a significant increase in spinal BMC and bone mineral density (BMD) in a group of post-menopausal women, who consumed 40 grams of soy protein with naturally occurring isoflavones daily for six months. These are just two of more than 33 studies published, considering the impact of soy on bone mineral density and content. The same group of Chinese researchers mentioned in the above paragraph, conducted a further meta-analysis of the 10 best designed studies (selected from 33 published trials) that examined the effect of soy on BMD in the spine ¨C the area of the skeleton considered to be most sensitive to oestrogen loss during the menopause. Soy isoflavones were found to provide significant protection against actual bone loss in the spine of menopausal women ²² . Stronger effects on BMD were found when more than 90 mg isoflavones were consumed daily, and for at least six months.

The other interesting learning from the meta-analysis on soy and BMD was that there appears to be teamwork going on between the isoflavones in soy and other important nutrients contained in soy protein or soy foods. If the isoflavones were provided to the women naturally packaged as part of the soy protein, there was a more significant effect in preventing bone loss. This may help to explain the lack of benefit seen in a recent study of postmenopausal women from three European countries given biscuits and bars enriched with isoflavones but not containing the broader range of nutrients found in whole soy foods ²³ . This finding is similar for many other nutrients from foods, where they act more beneficially when consumed as part of the natural food matrix, rather than being extracted and provided in a more purified and singular form. For example, beta-carotene supplied through fruits and vegetables is linked with protection from cancer but it has a neutral effect or may even cause cancer, when given as a nutrient, away from its natural food sources.

Another factor that is thought to determine how women respond to soy, is their ability to produce a substance called equol. This is made by the bacteria that live in the bowel from daidzein, one of the isoflavones supplied by soybeans. It is then absorbed into the bloodstream where it seems to have more potent effects in the body than the isoflavones obtained directly from soy. A double-blind, randomized, controlled study of Japanese postmenopausal women given isoflavones for a year, clearly showed superior results in preventing bone loss and body fat accumulation (which also more readily occurs after the menopause), among those women who were equol producers ²⁴ . This supports the earlier findings by Dr Kenneth Setchell, from the University of Cincinnati, where equol producers showed a significant increase in their lumbar spine BMD whereas no significant change was observed in the BMD of the nonproducers after a two year isoflavone intervention ²⁵ .

Unfortunately, it appears that only 30-50 % of individuals are capable of making equol (although Asians and vegetarians seem to be more likely to do so). The search is now on for lifestyle factors that may switch on our equol producing capability, as this might benefit other areas of health, not just bones.