Isoflavone content of foods with soy additives

The health effects of consumption of isoflavones from soy products are being actively investigated, yet food composition tables often have incomplete values for commercial foods containing soy additives. Therefore, we analyzed 167 processed and fast foods with soy additives (e.g. isolated soy protein, soy protein concentrate, soy flour, and hydrolyzed soy protein) for the isoflavones daidzein, glycitein, and genistein. Total isoflavones were computed by adding these three isoflavones. Additionally, 12 traditional soybean products were analyzed, including soy flour and Asian condiments made from soybeans. Foods were sampled from food stores and fast-food restaurants in Hawaii. Concentrations of total isoflavones, expressed as aglycones, ranged from not detected (ND, for 49 foods) to 149.9 mg/100 g. Ranges within food groups were: bread and grain products (ND-93.9), gravies and sauces (ND-2.7), meat and poultry products (ND-15.9), meat substitutes (0.3-149.9), nutritional products (0.4-36.5), reduced fat peanut butters (0.1-4.0), seafood products (ND-1.6), and soybean products (2.9-109.3). For 56 foods on our food composition table, we calculated composite isoflavone values reflecting the mean of multiple brands and the proportion of brands containing soy additives. The resulting table now permits more accurate estimates of total isoflavone intakes by participants in our research studies.