Dietary proanthocyanidins: occurrence, dietary intake, bioavailability, and protection against cardiovascular disease.

The French have one of the lowest incidences of coronary heart disease in the Western world despite a diet with a relatively high fat content. This phenomenon that has puzzled researchers worldwide for more than a decade is known as the 'French paradox' and has been linked to the high consumption of red wine in France. Red wine is rich in the complex polyphenols, the proanthocyanidins, and these compounds have recently attracted attention as potential cardiac-protective compounds. The present review summarizes the literature on proanthocyanidins with focus on their chemical structure, the occurrence, the daily intake from foods, the bioavailability and metabolism, and the evidence for a protective effect against cardiovascular diseases.

Urinary excretion of flavonoids reflects even small changes in the dietary intake of fruits and vegetables.

BACKGROUND: Due to the random and systematic measurement errors associated with current dietary assessment instruments, there is a need to develop more objective methods of measuring the intake of foods of importance to human health. OBJECTIVE: The purpose of this study was to test whether urinary excretion of flavonoids could be used to identify subjects who are meeting Norwegian recommendations for fruit and vegetable intake (5 servings per day) from individuals who are consuming the national average amount of fruits and vegetables (2 servings per day). DESIGN: Twenty-four-hour urine samples were collected in a strict crossover controlled feeding study. Forty healthy subjects (19-34 years) were included in the study. After a 1-week run-in period, one group was given a controlled diet that included 2 servings (300 g) of fruits and vegetables daily for 14 days, while the other group was given a diet containing 5 servings (750 g) per day. Following a 2-week washout and a 1 week run-in period, the regimens were switched between the groups. RESULTS: An increased intake of mixed fruits and vegetables from 2 to 5 servings per day significantly enhanced urinary excretion of eriodictyol, naringenin, hesperetin, quercetin, kaempferol, isorhamnetin, and tamarixetin. The citrus flavonoids naringenin and hesperetin showed a steep dose-response relationship to dietary intake of fruits and vegetables, whereas the association to eriodictyol, quercetin, kaempferol, isorhamnetin, and tamarixetin was more moderate. CONCLUSION: The present study indicates that urinary excretion of dietary flavonoids may be used to assess changes of mixed fruit and vegetable intake corresponding to an increase from the present national intake in Norway to the recommended amount of 5 servings of fruits and vegetables daily.

Non-nutritive bioactive food constituents of plants: bioavailability of flavonoids.

Flavonoids are polyphenols widely distributed in the plant kingdom, and are present in fruits and vegetables regularly consumed by humans. In vitro metabolic studies of flavonoids in rat liver microsomes identified the 3',4'-dihydroxylated derivatives as the major metabolic endpoint. However, in vivo in rats almost none of this metabolite and only minor amounts of the 4'-monohydroxylated derivative was produced. Flavonoids with the 4'-monohydroxylated structure were generally not metabolised and were excreted unchanged in urine in higher amounts than other flavonoids investigated. It has for long been a controversy, whether flavonoids are absorbed as the intact glycoside or whether they have to be hydrolysed to the free aglycon prior to absorption. Recent data suggest that beta-glucosidases and maybe also lactase phlorizin hydrolase (LPH) in the small intestine are capable of hydrolysing flavonoid glucosides and these compounds are thus taken up as the free aglycon and not as the intact glycosides. LC-MS analyses of 12 dietary flavonoids in human urine showed that no flavonoid glycosides were excreted, and that the citrus flavanones and phloretin are excreted in higher amounts than the flavonols. Furthermore, total flavonoid excretion may be a useful biomarker for habitual fruit and vegetable consumption.