Soy protein antioxidant actions in active, young adult women

Verification of the idea that soy exerts antioxidant effects in humans is limited. The present study examined intake of soy protein or a control whey protein (protocol of 40 g protein/day, 4 weeks). Soy protein, but not whey, depressed values for one oxidant stress marker (plasma lipid peroxides), though neither protein affected another marker (urinary 8-hydroxy-2-deoxyguanosine). Soy protein, but not whey, raised plasma antioxidant capacities based on the total antioxidant status (TAS) assay. This effect seemed not to simply reflect increased plasma isoflavone contents since spiking plasma in vitro with isoflavones had no major effect on TAS values. The TAS effect also did not result from increased plasma uric acid values since these were unchanged by soy protein. These results suggest that 4 weeks of soy intake exerts some antioxidant effects but not others. (C) 2002 Elsevier Science Inc. All rights reserved.