The dietary flavonoid values in our study were obtained from the database of flavonoid values for USDA Survey Foods and Beverages (flavonoid database for short), which was established in 2003–2004 [19 ]. The flavonoid database provides the flavonoid values in foods and beverages in the USDA Food and Nutrient Database for Dietary Studies (FNDDS) [20 ] and corresponding dietary data from WWEIA [21 ] and NHANES. The amounts of 29 flavonoids (mg/100 g) in each food/beverage were determined by the USDA Nutrient Data Laboratory [22 (link)]. The dietary intake of flavonoids was calculated on days 1 and 2, including the six main flavonoid subclasses commonly consumed in the US diet, namely total anthocyanins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin), total flavan-3-ols ((-)-epicatechin, (-)-epicatechin 3-gallate, (-)-epigallocatechin, (-)-epigallocatechin 3-gallate, (+)-catechin, (+)-gallocatechin, theaflavin, theaflavin-3,3′-digallate, theaflavin-3′-gallate, theaflavin-3-gallate, and thearubigins), total flavanones (eriodictyol, hesperetin, and naringenin), total flavones (apigenin and luteolin), total flavonols (isohamnetin, kaempferol, myricetin, and quercetin), total isoflavones (diadzein, genistein, and glycitein), and subtotal catechins ((-)-epicatechin, (-)-epicatechin 3-gallate, (-)-epigallocatechin, (-)-epigallocatechin 3-gallate, (+)-catechin, and (+)-gallocatechin). The retention factors for cooked foods were introduced in the estimation of the flavonoid amounts. For moist-heat cooking, a loss of 50% was applied to anthocyanidins, as well as one reduction of 15% to flavonols, flavan-3-ols, flavanones, and flavones. No retention factors were implemented for isoflavones and dry heat cooking [20 ]. The association between individual flavonoid intake grouped by flavonoid subclasses was analyzed using the Pearson correlation method.
Based on the stratified and multistage probability sampling designed in the NHANES, we used the mean of the two-day intake of each flavonoid, as well as the weights “wtdr2d” constructed for participants who completed two days of dietary recall in making estimates representative of the US non-hospitalized population [18 ].
Based on the stratified and multistage probability sampling designed in the NHANES, we used the mean of the two-day intake of each flavonoid, as well as the weights “wtdr2d” constructed for participants who completed two days of dietary recall in making estimates representative of the US non-hospitalized population [18 ].
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