The aim of this study is to determine by isoelectric focusing the level of AMPKa1, an energy sensor, in sera of patients who are in energy-demanding situation. After Western blotting, detection was performed with specific antibodies against AMPKa and its phosphorylated form. To evaluate the effect of weight loss on AMPK, sera from 24 patients were collected before and after intragastric balloon insertion over a 16-week follow-up period. Compared to baseline, all patients showed postoperatively an increase of AMPK. Patients with ischemic heart, with inflammatory bowel disease, with chronic undernutrition or with hepatic diseases were examined. Compared to control subjects, the majority of them showed a significant increase of AMPK. These results suggest that serum AMPK may have a potential for diagnosis of several metabolic diseases. However, this has to be confirmed by further studies with additional biomarkers and with more specific techniques.