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The effectiveness of soy isoflavones to prevent bone loss in postmenopausal women is controversial. While consumption of soy in Vietnam is very high, we recently reported a prevalence of osteoporosis comparable to that of many Western populations. In the present study, we analyzed the isoflavone content of soy drink products commercially available in Vietnam and Sweden, and we also compared these products to "home-made" soy drink from beans of different origin. The amounts of the bioactive aglycones (daidzein, glycitein and genistein) and their glycoside isomers were quantified by high-pressure liquid chromatography. We found that the total isoflavone content was low in all preparations, around 70-100 mg/L and of this only 10% were bioactive aglycones. Of these, the Vietnamese products contained significantly lower levels of glycitein than the products from Sweden and "home-made" soy drink preparations. The results show that consumption of several liters of soy drink per day would be needed to achieve threshold levels for a protective effect on bone. There was no significant association between total protein and isoflavone content in different products. Accurate labeling of soy drink and other products eg of aglycone and glycoside content would allow health professionals and researchers to better explore the possible benefits of soy in dietary intervention studies.