Context: Although metabolic abnormalities are often developed in Asians with body mass index (BMI) of 23-25 kg/m2, the characteristics of the nonobese Asians with metabolic abnormality have not been fully understood. Objective: The aim of this study was to investigate the clinical significance of insulin sensitivity in Japanese men with BMI of 23-25 kg/m2. Design and Participants: In this study, we defined hypertension, hyperglycemia, and dyslipidemia as cardiometabolic risk factors (CMRFs). We recruited subjects who met the following selection criteria: men with BMI of 21-23 kg/m2 and no CMRF (n = 24); men with BMI of 23-25 kg/m2 and no CMRF (n = 28), or one CMRF (n = 28), or at least two CMRFs (n = 14); and overweight men with metabolic syndrome (n = 20). Insulin sensitivity (IS) and ectopic fat content in muscle and liver were measured by two-step hyperinsulinemic-euglycemic clamp and 1H-magnetic resonance spectroscopy, respectively. Results: Among subjects with BMI of 23-25 kg/m2, impaired IS in muscle, but not in liver, was found in those with even one CMRF, whereas impaired IS in both muscle and liver was observed in overweight men with metabolic syndrome. Liver fat accumulation and elevated liver enzymes were associated with impaired IS in both muscle and liver in those subjects. Conclusions: Among Japanese men with BMI of 23-25 kg/m2, muscle insulin resistance was present in those with even one CMRF. In this population, liver fat accumulation and/or elevated liver enzymes could be a good marker for impaired IS in both muscle and liver.
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