Background Carboxylated osteocalcin (Gla‐OC) participates in bone remodeling, whereas the undercarboxylated form (Glu‐OC) takes part in energy metabolism. This study was undertaken to compare the blood levels of Glu‐OC and Gla‐OC in nonobese, healthy obese, and prediabetic volunteers and correlate it with the metabolic markers of insulin resistance and early markers of inflammation. Methods Nonobese (body mass index [BMI] <30 kg/m2 ; n = 34) and obese subjects (30 <BMI <40 kg/m2 ; n = 98), both sexes, aged 25 to 65 years, were divided into healthy control, normal weight subjects, healthy obese, and obese with biochemical markers of prediabetes. The subgroups with obesity and low or high Gla‐OC or Glu‐OC were also considered for statistical analysis. After 2 weeks of diet standardization, venous blood was sampled for the determination of Gla‐OC, Glu‐OC, lipid profile, parameters of inflammation (hsCRP, interleukin 6, sE‐selectin, sPECAM‐1, and monocyte chemoattractant protein 1), and adipokines (leptin, adiponectin, visfatin, and resistin). Results Gla‐OC in obese patients was significantly lower compared to nonobese ones (11.36 ± 0.39 vs 12.69 ± 0.90 ng/mL, P = .048) and weakly correlated with hsCRP (r = −0.18, P = .042), visfatin concentration (r = −0.19, P = .033), and BMI (r = −0.17, P = .047). Glu‐OC was negatively associated with fasting insulin levels (r = −0.18, P = .049) and reduced in prediabetic individuals compared with healthy obese volunteers (3.04 ± 0.28 vs 4.48 ± 0.57, P = .025). Conclusions Decreased blood concentration of Glu‐OC may be a selective early symptom of insulin resistance in obesity, whereas the decreased level of Gla‐OC seems to be associated with the appearance of early markers of low grade inflammation accompanying obesity.