A study in which postmenopausal women substituted 25g of soy protein for meat showed no alteration in the women's calcium retention or indicators of bone and cardiovascular health.
"In a controlled feeding study, the effects of substituting 25g soy protein for meat on calcium retention and bone biomarkers were determined. Postmenopausal women (n=13) ate two diets that were similar, except that, in one diet, 25g high-isoflavone soy protein was substituted for an equivalent amount of meat protein (control diet), for seven weeks each in a randomized crossover design.
"After three weeks of equilibration, calcium retention was measured by labeling the two-day menu with Ca-47, followed by whole-body counting for 28 days," said Z.K. Roughead and colleagues, U.S. Department of Agriculture, Agricultural Research Service. "Urinary calcium and renal acid excretion were measured at weeks 3, 5 and 7. Biomarkers of bone and cardiovascular health were measured at the beginning and end of each diet."
Study results showed that "calcium was similarly retained during the control and soy diets (d 28, percent dose, mean ±pooled SD: 14.1 and 14.0±1.6, respectively)."
Additionally, "despite a 15%-20% lower renal acid excretion during the soy diet, urinary calcium loss was unaffected by diet. Diet also did not affect any of the indicators of bone or cardiovascular health," reported Roughead's team.
They concluded, "Substitution of 25g high isoflavone soy protein for meat, in the presence of typical calcium intakes, did not improve or impair calcium retention or indicators of bone and cardiovascular health in postmenopausal women."
Roughead and coauthors published their study in the Journal of Clinical Endocrinology and Metabolism (“Controlled Substitution of Soy Protein for Meat Protein: Effects on Calcium Retention, Bone and Cardiovascular Health Indices in Postmenopausal Women.” J Clin Endocrinol Metab, 2005;90(1):181-189).
For additional information, contact Z.K. Roughead, ARS, USDA; Grand Forks Human Nutrition Research Center; Grand Forks, ND 58202.