The antioxidant actions of single food items or extracts rich in flavonoids (e.g., apple and black currant juice, grape skin extract, tea extract and parsley) were evaluated in short-term human trials [Denmark; date not given]. An overall weak trend toward decreased lipid oxidation with increased polyphenol intake was observed. There was an increased oxidative stress response toward plasma proteins from food items rich in polyphenols and vitamin C and a decreased response when fruits and vegetables were omitted using a controlled diet. There also was a similar trend toward increased antioxidant enzymes in red blood cells, particularly GR and Gpx, with increased polyphenols or vitamin C.