Iron indexes and total antioxidant status in response to soy protein intake in perimenopausal women

BACKGROUND: Elevated iron stores, oxidative stress, and estrogen deficiency may place postmenopausal women at greater risk of heart disease and cancer than premenopausal women. OBJECTIVE: The objective was to determine the effect of soy-protein isolate (SPI) intake and iron indexes on plasma total antioxidant status (TAS) in perimenopausal women after control for other contributing factors. DESIGN: Perimenopausal women (n = 69) were randomly assigned (double blind) to treatment: isoflavone-rich SPI (SPI+; n = 24), isoflavone-poor SPI (SPI-; n = 24), or whey protein (control; n = 21). Each subject consumed 40 g soy or whey protein daily for 24 wk. Plasma TAS, serum ferritin, serum iron, transferrin saturation, and hemoglobin were measured at baseline, week 12, and week 24. RESULTS: No significant time-by-treatment interactions on iron indexes or TAS were observed, whereas time had an effect on serum ferritin (P < or = 0.0001) and hemoglobin (P = 0.004) but not on TAS. Multiple regression analysis showed that at week 12, 48% (P < or = 0.0001) of the variability in TAS was accounted for by baseline TAS, alcohol intake, soy intake (soy compared with control; P = 0.016), plasma lipoprotein(a), and dietary iron. At week 24, 47% of the variability in TAS was accounted for by baseline TAS, serum ferritin, serum estrone, dietary zinc, and dietary meat, fish, and poultry. CONCLUSIONS: SPI intake had no significant effect on iron status, but our results suggest that dietary soy protein and low iron stores may protect perimenopausal women from oxidative stress.