Introduction: Insulin resistance (IR), a pathological state of low sensitivity to insulin in humans and animlas, is closely associated with type 2 diabetes mellitus, obesity and cardiovasculare dieseas. IR can be quantified using detailed protocols, such as the euglycemic-hyperinsulinemic clamp (EC) technique and the intravenous glucose tolerance test, or based on indices derived from the oral glucose tolerance test. Although these indices showed greater association with the incidence of diabetes, they allow no personalized estimation of the individual risk and cannot be used for monitoring of the individual changes in the insulin resistance. The modification of nutritional pattern is one of the first steps of prevention the IR and associated diseases. Diets with increased intake of branched chain amino acid lead to increase in IR in animals and human, possibly via disruption of insulin signaling in skeletal muscle. Here we aimed to investigate the changes in the plasma metabolome during constant insulin infusion. Additionally, the correlations between baseline concentrations of metabolites and changes of IR, which was measured in the EC-experiments, after high-protein and control diet were studied. Methods: In the first study (NCT00774488), middle-aged healthy obese subjects (n=14) underwent saline infusion and/or EC at a steady-state capillary plasma glucose concentration of 4.4 mmol/l. Plasma metabolites were measured using time-of-flight gas chromatography-mass spectrometry (GC-TOF/MS) technique. In the second study (NCT00579657), a randomized, controlled nutritional intervention (18-weeks) was conducted in 72 non-diabetic participants (overweight/obese: 29/43) with at least one further risk factor of metabolic syndrome. Participants were group-matched and allocated to 4 isoenergetic supplemented diets: control; high cereal-fiber; high-protein; or moderately increased cereal-fiber and protein (MIX). Whole-body IR was measured using EC. Plasma metabolome and IR were studied at 0, 6 and 18-weeks. Results: Eight metabolites: altrose, asparagine, glycerol-2-phosphate, gulose, heptadecanoic acid, phenylalanine, pyroglutamate and talose correlated with high-protein diet-induced changes in IR and significantly changed during EC. Conclusions: Multimarker strategy with use of plasma metabolic profiling appears to be a useful tool for both the assessment of IR and the ‘metabolic signature of insulin effects’ (i.e. doping control of elite athletes) in humans.