We investigated the relationship between insulin reaction and glycemic control in a 75-g oral glucose tolerance test of lipid in the paraspinal muscles using computed tomography (CT). The subjects were 79 males aged from 30 to 60 years old whose body mass index (BMI) was 25 or more. Those who had already been diagnosed as having type-2 diabetes mellitus in a regular health check and whose fasting plasma glucose was 126 mg/dl or more were excluded. Abdominal CT scan at the umbilicus level was conducted, and the visceral fat area (VFA) and subcutaneous fat area (SFA) were obtained. As an index of the relative lipid content within muscle, the mean skeletal muscle attenuation (MA) was determined. The age-adjusted odds ratio caused by the MA size for each variable was calculated. Compared with those with smaller intramuscular fat volume, those with larger volume demonstrated 8.75 times higher BMI, 3.73 times higher VFA and 2.88 times higher HOMA-IR. A significant difference was observed between the groups with high and low lipid content in the muscle in the values of Age, BMI, VFA, Fasting immunoreactive insulin (IRI) and HOMA-IR. It was suggested that MA of the paraspinal muscles reflected fat content, and this regional body composition parameter was closely related to insulin secretion response and glycemic control.