Plasma concentrations of the flavonoids hesperetin, naringenin and quercetin in human subjects following their habitual diets, and diets high or low in fruit and vegetables

Objectives: To determine the fasting plasma concentrations of quercetin, hesperetin and naringenin in human subjects consuming their habitual diets, and diets either high or low in fruit and vegetables. To investigate whether plasma concentrations of flavanones can serve as biomarkers of their intake. Design: This was a cross-over, strictly controlled dietary intervention consisting of a 2 week baseline period, and two 5 week dietary periods with a 3 week wash-out period in between. The low-vegetable diet contained few fruit and vegetables and no citrus fruit. The high-vegetable diet provided various fruits and vegetables daily including on average one glass of orange juice, one-half orange and one-half mandarin. Subjects: Thirty-seven healthy females. Results: The high-vegetable diet provided 132mg of hesperetin and 29mg of naringenin. The low-vegetable diet contained no flavanones. The mean plasma hesperetin concentration increased from 12.2nmol/l after the low-vegetable diet to 325nmol/l after the high-vegetable diet. The respective increase for naringenin was from < 73.5nmol/l for all subjects to a mean value of 112.9nmol/l. The mean plasma quercetin concentration was 52nmol/l after the baseline period, during which habitual diets were consumed, and it did not change significantly during the intervention. Interindividual variation in the plasma levels of hesperetin and naringenin was marked and, after the baseline and wash-out periods, and the low-vegetable diet, a majority of the samples had plasma flavanone levels below the limit of detection. After the high-vegetable diet, hesperetin and naringenin were detectable in 54 and 22% of all samples. Quercetin was detectable in nearly all samples after all study periods. Conclusion: Hesperetin, naringenin and quercetin are bioavailable from the diet, but the plasma concentrations of hesperetin and naringenin are poor biomarkers of intake.