Many studies showed that soy foods or soy isoflavones can lower the risk of cardiovascular disease (CVD), osteoporosis and some cancers, but few human studies assessed effects of purified isoflavone components (genistein and daidzein) on glucose metabolism. This double-blinded, randomized, placebo-controlled trial will examine the effects of purified genistein and daidzein on glucose metabolism in prediabetic or diabetic women. One hundred and eighty eligible women age 30-70 years(without any treatment of diabetic drugs) will be recruited and randomly allocated into the following three arms: Placebo (10g isolated soy protein, ISP); Genistein (10g ISP + 50mg genistein); Daidzein (10g ISP + 50mg daidzein) per day for 6 mo. Fasting glucose, lipids, insulin, inflammation marks and post-load for glucose and insulin will be determined at 0, 3th, and 6th month. Changes in these indices will be compared among the three groups.