In this study, the antioxidant protection of ascorbic acid (AA) supplementation during different unfed periods (24, 48, 120 h) was determined with blood lipid peroxidation level (thiobarbituric acid reactive substances, TBARS) and compared with plasma antioxidant sulfydryl group (RSH) content. Weight loss was induced by increasing the unfed period together with vitamin C supplementation. Blood AA levels decreased by starvation but increased by vitamin C supplementation. RSH content in plasma also decreased with the unfed period; these decreases became apparent by vitamin C supplementation. TBARS formation increased significantly by AA supplementation in the 120-h starvation period. (C) 1999 Elsevier Science Inc. All rights reserved.