Data for the US population were calculated using the most updated USDA flavonoid and isoflavone databases, and the National Health and Nutrition Examination Survey (NHANES) III 24-h dietary recall. Estimated mean total flavonoid intake by US adults was 344.83 +/- 9.13 mg/day. Isoflavone intake was markedly lower, as average consumption was only 2.35 mg per day. Even among the “other” ethnic group, which excludes Mexican Americans and non-Hispanic whites and blacks, mean intake was only 5.23 mg. It is clear from these data that among the general US population soy intake is negligible since each gram of protein in traditional soyfoods is associated with about 3.5 mg isoflavones and each gram of isolated soy protein is associated with about 1 mg per gram.
In contrast to the low intake among the general population soy intake among vegetarians and vegans is significantly higher. The most comprehensive data on vegetarian soy intake come from a cross-sectional study of 71,751 participants (mean age=59 years) from the Adventist Health Study 2. Data were collected between 2002 and 2007. Participants completed a 204-item validated semi-quantitative food frequency questionnaire. Dietary patterns compared were nonvegetarian, semi-vegetarian, pesco vegetarian, lacto-ovo vegetarian, and strict vegetarian. Soy protein intake (g/d) increased in a step-wise fashion when going from non-vegetarian diet (4.9), to a semi-vegetarian one (8.0) to pesco-vegetarian (10.5) and lacto-ovovegetarian diets (10.2) and finally, to a vegan diet (13.1). Soy protein contributed 19.1% of total protein intake of the vegans. The non-vegetarian Seventh-day Adventists (SDA) consumed much higher amounts of soy protein than the general population, which is not surprising since even nonvegetarian SDAs have been shown to be more health-conscious than the general population.
Bai W, Wang C, Ren C. Intakes of total and individual flavonoids by US adults. Int J Food Sci Nutr 2013.
Rizzo NS, Jaceldo-Siegl K, Sabate J, et al. Nutrient profiles of vegetarian and nonvegetarian dietary patterns. J Acad Nutr Diet 2013.