Effect of soy food intake on mineral status in women of childbearing age

Many health benefits are attributed to soy food intake, but data on mineral balance are limited. Our main objective was to determine the effect of soy foods intake for 10-wk on iron or zinc status in women of childbearing age. We also tested the effect on bone and thyroid hormones. Women (18-28 y) non-smokers without chronic disease, anemia, pregnancy, and/or irregular menstrual cycles were randomly assigned to either a soy (n=31) or an animal food (n=32) group. Blood and urine samples and 3-d dietary records were collected prior to and after intervention. At baseline, iron and zinc status, biochemical markers of bone, and thyroid hormones were not different between two groups. After intervention, no significant changes were observed in hemoglobin, transferrin saturation, serum iron, ferritin, or transferrin receptor concentrations, as well as the transferrin receptor-ferritin index. Intervention significantly decreased plasma zinc (5 yg/dl in each group) but not serum alkaline phosphatase (soy vs. animal food group: 1.1 vs. 1.2 IU/L) concentrations. Soy intake slightly increased (1.5 U/L) bone-specific alkaline phosphatase concentration, with the change being significantly different from the animal food group (-0.7 U/L). No significant changes were observed in bone resorption marker, thyroid stimulating hormone or free thyroxine after soy food intake. In conclusion, incorporating 2 servings/day of soy foods with ~20 g protein for 10-wk had no significant effect on iron and zinc status, bone resorption, or thyroid hormones and a beneficial effect on bone formation, compared to animal foods intake, in women of childbearing age