Taxonomic classification helps identify flavonoid-containing foods on a semiquantitative food frequency questionnaire

We describe foods on the National Cancer Institute (NCI) semiquantitative food frequency questionnaire with respect to their botanical taxonomic classification and the likely presence of flavonoids. Foods listed in the NCI questionnaire were classified for potential flavonoid content using information from Linnaean taxonomic classification and processing techniques known to modify flavonoid content. The outcome measure was flavonoid presence in foods as evidenced in the food composition analytical literature. We then verified the presence of 6 classes of flavonoids in these foods by searching the chemical analytical literature (represented by Food Science and Technology Abstracts Service from January 1969 to June 1996). One hundred ninety foods were mentioned on the NCI questionnaire; after duplications were removed, 153 foods remained. Data obtained from literature searches indicated that 54 foods (35%) contained flavonoids. An additional 19 recipe foods (12%) had flavonoid-containing components or ingredients. Thirty-nine foods (25%) had flavonoids that had been reduced or removed during milling and other processing. Seven foods (5%) were stripped and judged to have no flavonoids. Thirty-four foods (22%), for example, dairy, meat, and sugar, were completely devoid of flavonoids. When food composition data are unavailable, botanical taxonomic classifications may be helpful in ascertaining the likely presence of flavonoids in foods. However, quantitative estimates are likely to be imprecise.