Abstract Metabolic syndrome is a cluster of metabolic abnormalities that includes central obesity, insulin resistance, dyslipidemia, elevated blood pressure, and impaired glucose regulation. Evidence suggests that oxidative stress and chronic low-grade inflammation contribute to the development and progression of these abnormalities. Oxidative stress occurs when the production of reactive oxygen species exceeds the capacity of antioxidant defense systems to regulate their effects, potentially causing lipid, protein, and DNA damage, as well as mitochondrial dysfunction and altered cellular signaling. This review discusses the biochemical mechanisms linking oxidative stress to insulin resistance and disturbed lipid metabolism, with emphasis on lipid peroxidation markers, including malondialdehyde, and antioxidant defenses such as superoxide dismutase, catalase, and glutathione peroxidase. The limitations of these biomarkers in clinical interpretation and potential future therapeutic directions are also considered. Integrating oxidative stress markers with metabolic and inflammatory indicators may provide a more informative assessment than relying on a single biomarker. Nevertheless, further standardized studies are required before these markers can be routinely applied in clinical risk assessment. Keywords: Oxidative stress; metabolic syndrome; insulin resistance; antioxidant defense; malondialdehyde; antioxidant enzymes. 1. Introduction Metabolic syndrome is a multifactorial condition associated with an increased risk of type 2 diabetes mellitus and cardiovascular disease. Its development involves genetic, environmental, and behavioral factors, together with abnormalities in adipose tissue function and glucose and lipid metabolism. Oxidative stress is one biochemical pathway potentially linking excess adiposity to inflammation and impaired insulin signaling. It develops when reactive oxygen species production exceeds the capacity of cellular antioxidant systems to maintain redox balance. However, reactive oxygen species also participate in normal cellular signaling; therefore, their biological effects depend on their concentration, location, and duration of exposure. 2. Biochemical mechanisms of oxidative stress 2.1. Generation of reactive oxygen species Reactive oxygen species arise from several sources, including the mitochondrial electron transport chain, NADPH oxidases, and other enzymatic reactions. Sustained excess production may promote cellular oxidation and interfere with normal cellular functions. 2.2. Lipid peroxidation Polyunsaturated fatty acids in cellular membranes are susceptible to oxidation, producing secondary compounds such as malondialdehyde. These compounds can serve as research indicators of oxidative damage, although their measured levels depend on analytical methods and laboratory conditions. 2.3. Mitochondrial dysfunction Oxidative stress may impair mitochondrial function and energy production. These changes can interfere with fatty acid and glucose metabolism and may contribute to the persistence of metabolic dysfunction. 3. Oxidative stress and insulin resistance Oxidative and inflammatory signals can affect cellular pathways involved in insulin responsiveness. Chronic inflammation in adipose tissue may alter cytokine and adipokine secretion, thereby influencing glucose and lipid regulation. These processes interact with mitochondrial dysfunction and oxidative stress, although their relationships are complex and cannot be attributed to a single pathway. 4. Biomarkers of oxidative stress and antioxidant defense Commonly investigated biochemical markers include: Malondialdehyde (MDA): An indirect indicator of lipid peroxidation. Superoxide dismutase (SOD): Catalyzes the conversion of superoxide radicals into hydrogen peroxide. Catalase (CAT): Contributes to hydrogen peroxide decomposition. Glutathione peroxidase (GPx): Reduces hydrogen peroxide and lipid hydroperoxides using glutathione. Reduced glutathione (GSH): An important component of cellular antioxidant defense. These markers should be interpreted alongside metabolic indicators such as fasting glucose, triglycerides, and high-density lipoprotein cholesterol, as well as inflammatory markers when appropriate. None of the listed oxidative stress markers independently establishes a diagnosis of metabolic syndrome. 5. Therapeutic perspectives Addressing metabolic risk factors through dietary quality, physical activity, adequate sleep, and appropriate weight management is central to reducing metabolic risk. Dietary patterns rich in vegetables, fruits, and sources of antioxidant compounds have been investigated for their potential benefits. However, antioxidant supplementation should not automatically be assumed to improve clinical outcomes, because effects vary according to the compound, dose, study population, and quality of evidence. Pharmacological interventions and supplements should be assessed using appropriate clinical evidence and professional guidance. 6. Research challenges and future directions Important challenges include variation in oxidative stress assays, the influence of age, diet, medications, and comorbidities, and the difficulty of establishing causal relationships between oxidative stress and insulin resistance. Future studies may benefit from combining oxidative, inflammatory, and metabolic biomarkers, standardizing laboratory procedures, and using longitudinal designs to evaluate changes over time. 7. Conclusions Oxidative stress is an important pathway associated with metabolic dysfunction in metabolic syndrome and interacts with chronic inflammation, mitochondrial impairment, and insulin resistance. Oxidative stress biomarkers may provide useful research information when interpreted within a broader panel of clinical and biochemical indicators. Further standardized research is needed to establish their predictive and clinical utility. References Birben, E., Sahiner, U. M., Sackesen, C., Erzurum, S., & Kalayci, O. (2012). Oxidative stress and antioxidant defense. World Allergy Organization Journal, 5, 9–19. https://doi.org/10.1097/WOX.0b013e3182439613 Mechanisms of Oxidative Stress in Metabolic Syndrome. (2023). International Journal of Molecular Sciences, 24(9), 7898. https://doi.org/10.3390/ijms24097898 Neeland, I. J., Lim, S., Tchernof, A., et al. (2024). Metabolic syndrome. Nature Reviews Disease Primers, 10, 77. https://doi.org/10.1038/s41572-024-00563-5