Comparison of Estimated and Measured Isoflavone Content of Foods Commonly Consumed by Adventists in the United States and Canada

Agricultural, growth, and genetic factors; storage, and processing techniques can have an effect on isoflavone content in foods, and may contribute to differences between food composition databases and content measured by chemical analyses. Errors in estimating nutrient composition of dietary exposure variables can contribute to mixed research findings in evaluating the association between diet and disease. The objective of this study was to compare estimated and measured soy isoflavone content of soy food products. Thirty‐eight most frequently consumed soy food items were identified based on 40,000 responses to the Adventist Health Study‐2 food frequency questionnaire (FFQ). The FFQ included 51 soy‐containing food items and open‐ended questions about the use of meat analogues and soy milk. Soy protein and isoflavone content (in aglycone equivalents) estimates were based on the soy ingredients contained in recipes. The isoflavone content of these 38 food items was measured by liquid chromatography methods on two samples of each food. Corrected (to remove the measured isoflavone between and within variance) Spearman correlations were calculated between estimated and measured isoflavone content. The estimated total isoflavones from meat analogs and soymilk ranged from 0.19 to 225 μg/g. Estimates for daidzein, genistein, and glycitein were 0.08 to 82, 0.07 to 116 and 0.04 to 27 μg/g respectively. Mean laboratory measures of aglycone content ranged from 0.00 to 24 μg/g for daidzein, 0.00 to 31 μg/g for genistein, and 0.00 to 5 μg/g for glycitein. Mean measured glucosides ranged from 0.00 to 292, 0.14 to 345, and 0.00 to 28 μg/g for daidzin, genistin, and glycitin respectively. Mean measures of total isoflavone (aglycones plus glucosides) content was 0.45 to 699 μg/g. Estimated isoflavone content was moderately correlated with measured aglycones (r=0.56 for total; r=0.53 for daidzein, r=0.66 for genistein), except for a weak correlation with glycitein (r=0.32). Estimated isoflavone content was moderately correlated with measured glucosides (r=0.63) and total measured isoflavones (r=0.64). The correlation between estimated soy protein and total measured isoflavones was 0.61. Observed moderate correlations, indicate that our estimated isoflavone content may be a good measure of actual content. Support or Funding Information McClean Funds for Nutrition Research