Introduction: Cholecystokinin (CCK) and peptide YY (PYY) are satiety-stimulating hormones that are released during eating. As such, their levels may be used useful in obesity intervention. The aims of this study were to determine the optimal cutoff values, sensitivity and specificity of plasma CCK and PYY in adult men, in order to determine hormonal dysfunction in obesity. Methods: We investigated 16 obese [body mass index (BMI) ≥25.1)] and 16 normal weight (BMI 18.5–22.9) men. They ate isocaloric fast-food for breakfast. Blood for the determination of the hormones was collected at 0 (before), 30, 60, and 120 minutes after consumption. The data that was obtained were analysed using an independent t-test or the Mann– Whitney U-test. The receiver operating characteristic (ROC) curve was drawn and the trapezoidal rule analysis was performed to determine the area under the curve, to determine the optimal cut-off values, sensitivity and specificity. Results: In obese subjects, CCK was lower compared with normal weight subjects at any time (p<0.05). There were no major differences in PYY among subject groups. ROC curve analysis demonstrated that the plasma CCK had an optimal cut-off of 6,310 pg/ ml at 120 minutes after eating, with 0.97 area under curve (AUC), sensitivity was 94%, and specificity was 94%. The cut-off for optimal PYY was an average of 294.5 pg/ml at 120 minutes after eating (AUC 0.74; sensitivity 75%; specificity 75%). Conclusion: Our findings suggest that the plasma CCK level is a better potential predictor of obesity and constantly decreased over time compared to PYY.