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

Elevated iron stores, oxidative stress, and estrogen deficiency may place postmenopausal women at greater risk of heart disease and cancer than premenopausal women.

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.

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.

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.

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.