The current study investigated whether sardine protein mitigates the adverse effects of fructose on plasma glucagon‑like peptide-1 (GLP-1) and oxidative stress in rats. Rats were fed casein (C) or sardine protein (S) with or without high‑fructose (HF) for 2 months. Plasma glucose, insulin, GLP‑1, lipid and protein oxidation and antioxidant enzymes were assayed. HF rats developed obesity, hyperglycemia, hyperinsulinemia, insulin resistance and oxidative stress despite reduced energy and food intakes. High plasma creatinine and uric acid levels, in addition to albuminuria were observed in the HF groups. The S‑HF diet reduced plasma glucose, insulin, creatinine, uric acid and homeostasis model assessment‑insulin resistance index levels, however increased GLP‑1 levels compared with the C‑HF diet. Hydroperoxides were reduced in the liver, kidney, heart and muscle of S‑HF fed rats compared with C‑HF fed rats. A reduction in liver, kidney and heart carbonyls was observed in S‑HF fed rats compared with C‑HF fed rats. Reduced levels of nitric oxide (NO) were detected in the liver, kidney and heart of the S‑HF fed rats compared with C‑HF fed rats. The S diet compared with the C diet reduced levels of liver hydroperoxides, heart carbonyls and kidney NO. The S‑HF diet compared with the C‑HF diet increased the levels of liver and kidney superoxide dismutase, liver and muscle catalase, liver, heart and muscle glutathione peroxidase and liver ascorbic acid. The S diet prevented and reversed insulin resistance and oxidative stress, and may have benefits in patients with metabolic syndrome.