Controlled substitution of soy protein for meat protein: Effects on calcium retention, bone, and cardiovascular health indices in postmenopausal women

In a controlled feeding study, the effects of substituting 25 g 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, 25 g high-isoflavone soy protein ( SOY) was substituted for an equivalent amount of meat protein ( control diet), for 7 wk each in a randomized crossover design. After 3 wk of equilibration, calcium retention was measured by labeling the 2-d menu with Ca-47, followed by whole-body counting for 28 d. Urinary calcium and renal acid excretion were measured at wk 3, 5, and 7. Biomarkers of bone and cardiovascular health were measured at the beginning and end of each diet. 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). 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. Substitution of 25 g 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.