Chronic systemic inflammation is essential in many chronic non-infectious diseases, including type 2 diabetes, obesity and metabolic syndrome (MS). This study aimed at characterization of systemic inflammatory reaction as a component of diet-induced MS in rat model. Thirty-three male Wistar rats were distributed into two groups designated 'control' (n = 15) and 'experimental (MS)' (n = 18). The groups were fed, respectively, regular and high-fat/high-carbohydrate diets for 12 weeks. The intensity of systemic inflammatory process against the background of metabolic impairments was assessed by total and differential counts of white blood cells and serum levels of total protein, C-reactive protein, cytokines (IL6, IL10 and TNFα), insulin and leptin. We also assessed the production of reactive oxygen species in adipose tissue samples. The experiment revealed signs of systemic inflammation in MS as compared to control, including reactive leukocytosis, hyperproteinemia and increased serum levels of C-reactive protein (2.6-fold; р = 0.001), IL10 (3.7-fold; р = 0.029) and TNFα (4.2-fold; р = 0.035). The observed changes were accompanied by elevated metabolic activity of visceral adipose tissue, indicated by hyperleptinemia and increased free radical oxidation intensity. Pairwise positive correlations of serum levels were revealed for leptin and insulin (r = 0.701; р = 0.001) and leptin and IL10 (r = 0.523; р = 0.012). Thus, high-fat/ high-carbohydrate diet promoted metabolic impairments concomitantly with early signs of systemic inflammation characteristic of MS and obesity.