Free fruit at workplace intervention increases total fruit intake: a validation study using 24 h dietary recall and urinary flavonoid excretion

Background/Objectives: To validate 24 h dietary recall of fruit intake by measuring the total 24 h excretion of 10 different flavonoids in 24 h urine during an intervention with free fruit at workplaces. Subjects/Methods: Employees at workplaces offering a free-fruit program, consisting of daily free and easy access to fresh fruit, and controls employees at workplaces with no free-fruit program were enrolled in this validation study (n = 103). Dietary intake was assessed by using a 24 h dietary recall questionnaire at baseline and approximately 5 months later. Ten flavonoids, quercetin, isorhamnetin, tamarixetin, kaempferol, hesperetin, naringenin, eriodictyol, daidzein, genistein, and phloretin, were measured using HPLC-electrospray ionization-MS. Results: The 24 h urinary excretion of total flavonoids and the estimated intake of fruits were significantly correlated (r(s) = 0.31, P<0.01). The dietary intake of citrus fruits and citrus juices was significantly correlated with total excretion of citrus specific flavonoids (r(s) = 0.28, P<0.01), and orange was positively correlated with naringenin (r(s) = 0.24, P<0.01) and hesperetin (r(s) = 0.24, P<0.01). Phloretin in urine was correlated with apple intake (r(s) = 0.22, P<0.01) and also with overall estimated intake of fruit (r(s) = 0.22, P<0.01). Conclusions: This study shows that a 24 h dietary recall can be used as a valid estimate of the intake of fruits in agreement with an objective biomarker of fruit intake in free fruit at workplace interventions. European Journal of Clinical Nutrition (2010) 64, 1222-1228; doi:10.1038/ejcn.2010.130; published online 4 August 2010