Bone and Soy

A review of the current research is confusing regarding the effect of soy on bone. What we do know is that soy contains phytoestrogens or plant estrogens. During menopause estrogen levels drop in women and so does their bone density. The soy phytoestrogens called isoflavones act like a weak form of estrogen and may help to preserve bone. In several studies, soy isoflavones' influence on bone has been investigated.

The scientific results presented at the Fourth International Symposium on the Role of Soy in Preventing and Treating Chronic Disease are conflicting. Eva Lydeking-Olsen, from the Institute for Optimal Nutrition in Denmark, found that postmenopausal women eating a diet with a high isoflavone soymilk had an increase in spinal bone mineral density (BMD) whereas, the spine BMD of women eating a soymilk low in isoflavones decreased. However, Mara Vitolins, from Wake Forest University, found no differences in BMD at any bone site when women ate soy protein. Lisa Spence, from Purdue University, also showed no differences in BMD between women who ate a low and women who ate a high isoflavone diet. However, epidemiological studies do suggest that a higher isoflavone intake is associated with a higher BMD. So why all the conflicting information? The study designs, the age of the subjects, the number of subjects, and the length of the studies all contribute to conflicting results regarding soy. Research studies are only beginning to determine the effects of soy on bone health.

Apart from the possible beneficial effects of soy isoflavones on bone, substituting soy protein for animal protein may reduce the loss of calcium in the urine. Since 99% of the body's calcium is stored in the bones, eating soy may preserve calcium thus, may preserve bone. On a gram basis, soy protein causes less calcium to be lost in the urine than animal protein. In addition, soy foods provide high quality protein, are low in saturated fat, and are a good source of essential fatty acids. The Food and Drug Administration announced diets low in saturated fat and cholesterol that include 25g of soy protein a day may reduce the risk of heart disease.

The relationship between soy and bone is unclear at this time. However, adding soy to any diet will add variety. Variety, balance and moderation are the keys to a healthy diet