Effects of soy isoflavone consumption on bone structure and milk mineral concentration in a rat model of lactation-associated bone loss

Like menopause, during complete lactation, circulating estrogen concentrations are markedly reduced, resulting in amplified bone resorption. To investigate the effects of soy isoflavones, common dietary components used to mitigate the bone loss of menopause, on the bone loss associated with lactation. Lactating rats were randomized to one of four diets supplemented with different levels of soy isoflavones (0, 2, 4, 8 mg aglycone isoflavone/g protein). Milk was collected from all dams between days 12 and 15 of lactation and was analyzed for calcium, phosphorus and genistein concentrations. Serum and bones from half of the animals from each diet group were taken at weaning and from the remaining half at 4 weeks post-weaning. Bones underwent histomorphometric analysis and serum was used for genistein determinations. Serum genistein and milk concentrations reflected dietary isoflavone dose. Isoflavone intake had no effect on any of the bone changes associated with lactation or recovery. Milk calcium and mineral concentrations were unaffected by dietary isoflavones. Consumption of soy isoflavones, in levels that can be readily attained through soy foods, have neither protective effects on bone nor deleterious effects on milk quality or quantity during lactation.