The effect of thermally oxidized sunflower oil ingestion on antioxidant levels, enzyme activities and expressions in the small intestine of fed and fasted rats was studied. For three consecutive days, 12 male Wistar rats received 0.5 g of unused sunflower oil/100 g of body weight (controls, C) while another 12 were given 0.5 g of thermally oxidized sunflower oil/100 g of body weight (test group, T). On the night of day 3, 6 rats from each group were fasted (FC and FT, respectively) while the other 6 animals from each group were given free access to food (NFC and NFT, respectively). On day 4, FC and NFC rats received 1 g of unused oil/100 g of body weight, while FT and NFT rats were given 1 g of altered oil/100 g of body weight. Small intestines were extracted after 4 h exposure to the oils. Fasting and oil alteration significantly interacted modifying total, Se-GPx (both, P < 0.001) and non-Se-GPx (P < 0.05) activity, and GPx and Cu,Zn-SOD expressions (both P < 0.001). FT rats showed a significant increase in TBARS (P < 0.05) and catalase activity (P < 0.001) and a decrease in SOD, Se- and non-Se-dependent GPx activities (at least, P < 0.05) with respect to FC and NFT animals. SOD and GPx expressions decreased (p<0.001) but that of TNFalpha increased significantly (P < 0.001) in FT rats with respect to FC and NFT animals. Lengthy fasting and consumption of food containing oxidized fat should both be avoided to prevent intestinal oxidative stress.