ABSTRACTBACKGROUNDThe gastrointestinal tract (GI) is constantly exposed to reactive species released by the GI tract itself, and those present in food and beverages. Phenolic compounds may help in protecting the GI tract against damage produced by the reactive species. In this paper we have analyzed the effects of a grape seed proanthocyanidin extract (GSPE) on reactive oxygen species (ROS) production in two different intestinal cell types: the absorptive cell line Caco‐2 and the enteroendocrine cell line STC‐1.RESULTSWe show that GSPE prevents tert‐butylhydroperoxide‐induced oxidative stress in both cell lines, and that the effects are dose and time dependent. We have also analyzed whether GSPE has any in vivo effect, and found that 25 mg kg−1 body weight cannot counteract the increase in intestinal ROS induced by the cafeteria diet. However, an acute (1 h) treatment of 1 g GSPE kg−1 body weight reduced ROS in fasted animals and also decreased ROS induction by food. These effects were found only after a short‐term treatment. Furthermore, we have compared the in vitro GSPE effects with those of another proanthocyanidin‐rich extract from cupuassu seeds, though it has compounds with different structures. Cupuassu extract also shows antioxidant effects in both cell types, which suggests different mechanisms from those of GSPE.CONCLUSIONNatural proanthocyanidin‐rich extracts have an antioxidant effect in the GI tract, acting on absorptive cells and enterohormone‐secreting cells, although the effects depend on the dose and period of treatment. © 2015 Society of Chemical Industry