BACKGROUND: Weight loss through low-calorie diets (LCDs) decreases visceral fat (VF). However, the effects on muscle mass, changes of dietary quality, and insulin sensitivity are unknown for Korean obese type 2 diabetic subjects. Therefore, this study examined such effects of LCDs. METHODS: A total of 30 obese type 2 diabetic subjects (body mass index, 27.0 +/- 2.2 kg/m2) were randomly assigned to an LCD or control group. Subjects on LCDs took 500~1,000 kcal fewer energy than their usual dietary intake (1,000~1,500 kcal/day) over the course of 12 weeks. The abdominal VF and femoral muscle mass were evaluated by computed tomography, and insulin sensitivity was assessed using an insulin tolerance test (Kitt; rate constant for plasma glucose disappearance, %/min). Dietary nutrient intake consumed by subjects was assessed by 3-day food records. RESULTS: The percent VF reduction was -23.4 +/- 17.2% in the LCD group and -9.8 +/- 11.8% in the control group after 12 weeks (P < 0.001, P = 0.002). However, significant decrease in femoral mass or proportional change of marcronutrient intake and mean adequacy ratio were not found in the LCD group, as compared to the control group. Insulin sensitivity improved in the LCD group, as compared to the control group (P = 0.040). CONCLUSION: LCD effectively improved insulin sensitivity and reduced abdominal VF without reduction of femoral muscle and dietary quality in obese type 2 diabetic subjects.