Sex-Specific Cytokine Responses and Metabolic Adaptation to Weight Loss in Obesity with Insulin Resistance

Background/Objectives: Obesity-related insulin resistance is accompanied by chronic low-grade inflammation, but the extent to which weight loss modifies circulating cytokines in a sex-specific manner remains insufficiently understood. The aim of this study was to assess sex-specific cytokine responses and metabolic adaptation in adults with obesity and insulin resistance following a six-month weight-reduction program (WRP). Methods: Thirty-six participants (24 women and 12 men) with a value of Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) ≥ 2 underwent an individualized low-calorie diet combined with moderate physical activity and health education. Anthropometric, body composition, biochemical, oxidative stress, and cytokine parameters were evaluated before and after the intervention. Results: Both women and men showed significant reductions in body mass, Body Mass Index (BMI), waist circumference, visceral fat area (VFA), body fat mass (BFM), fasting glucose, HOMA-IR, modified Atherogenic Index of Plasma (new-AIP), malondialdehyde (MDA), and Oxidative Stress Index (OSI). Women additionally showed significant decreases in fat-free mass (FFM), skeletal-muscle mass (SMM), total body water (TBW), glycated hemoglobin A_1c (HbA1c), and triacylglycerols, whereas cholesterol in high-density lipoproteins (HDL-C) increased significantly in men. Cytokine changes were selective rather than uniform. Interleukin-1 receptor antagonist (IL-1ra), Interleukin 6 (IL-6), and Tumor Necrosis Factor alpha (TNF-α) decreased in both women and men. In sex-stratified analyses, IL-1β decreased significantly only in women, whereas IL-7 decreased significantly only in men. ClinicalTrials.gov Registration: [NCT07645105] (retrospectively registered on [11 June 2026]). Conclusions: A 6-month lifestyle-based weight-reduction program in adults with overweight or obesity and insulin resistance was associated with metabolic improvement, reduced oxidative stress, and partial attenuation of obesity-related low-grade inflammation. The observed cytokine and metabolic changes suggest sex-related patterns of immunometabolic adaptation to weight reduction. However, these findings should be interpreted cautiously because of the relatively small sex-stratified subgroups and the number of cytokine endpoints analyzed, and they require confirmation in larger, sex-balanced studies.