Obesity treatment is often burdensome for patients. We used the combination of moderate caloric restriction (CR) with hypoglycemic metformin to assess their multidirectional effect in obese patients. One group was treated only with moderate CR (n=21) the second was treated with moderate CR and 800 mg metformin twice daily (n=23). Serum was drawn before and after treatment. The following parameters were monitored: anthropometric, cardiovascular, inflammatory, metabolic, and markers characteristic for thyroid, liver, pancreas, and kidney functions. Both tested groups did not significantly differ in most tested parameters after the treatment. Two groups reduced anthropometric parameters (body mass, body mass index (BMI), waist circumference) and fat mass but also muscle and fat-free mass, improving systolic blood pressure, insulin and leptin concentration, insulin sensitivity, leptin to adiponectin ratio, and inflammatory markers. Unfortunately, there was little impact on improving dyslipidemia and the thyroid and liver parameters. Free triiodothyronine (fT3) and gamma glutamyl transferase (GGT) activity were decreased in both groups, but triglycerides were reduced only in patients treated with moderate CR. Metformin with CR treatment decreases uric acid and aspartate aminotransferase (AspAT) activity. Metformin treatment with moderate CR in obese patients mainly improved insulin sensitivity, resulting in a reduction of patients with glucose intolerance, improved anthropometric, cardiovascular, and inflammatory mediators, and only slightly enhanced liver and thyroid function. No changes in kidney and pancreas function were observed during the treatment. In conclusion, eight weeks of CR alone and CR with metformin in obese adults improved anthropometric and metabolic markers, reduced muscle mass, fT3, GGT, proinflammatory, and CV parameters, and displayed no changes in kidney and pancreas function. The group treated with metformin after the treatment was still more obese and had higher C-reactive protein (CRP) and homeostasis model assessment-an index of insulin resistance (HOMA-IR), but despite this, considerably reduced the number of patients with glucose intolerance.