although anthocyanins have been shown to have antioxidant properties "in vitro", there is no evidence for antioxidant effects in humans after consuming foods rich in anthocyanins. unlike controlled test-tube conditions, the fate of anthocyanins "in vivo" shows they are poorly-conserved (less than 5%), with most of what is absorbed existing as chemically-modified metabolites that are excreted rapidly. the increase in antioxidant capacity of blood seen after the consumption of anthocyanin-rich foods may not be caused directly by the anthocyanins in the food, but instead, by increased uric acid levels derived from metabolizing flavonoids (anthocyanin parent compounds) in the food. it is possible that metabolites of ingested anthocyanins are reabsorbed in the gastrointestinal tract from where they may enter the blood for systemic distribution and have effects as smaller molecules.