Intrahepatic lipid content is linked to insulin resistance in obese subjects

Abstract

Abdominal visceral fat (VAT) and intrahepatic lipid (IHL) are associated with insulin resistance in obese subjects, but VAT is usually measured on CT scans at the umbilical level or on MRI images of the partial abdomen. Thus, the association of the total abdominal visceral fat volume (VFV) with insulin resistance is unclear. In this study, we evaluated the correlations of obesity-related factors, including VFV and IHL, with clinical markers of insulin resistance (HOMA-R and the MATSUDA Index), and then assessed the effect of weight loss on these factors and markers. The study population consisted of 30 obese Japanese subjects with a BMI > 25 kg/m(2) (13 men and 17 women) who underwent a 75-g oral glucose tolerance test to calculate HOMA-R and the MATSUDA Index, dual energy X-ray absorptiometry (DEXA) for measurement of body fat (%-Fat), proton magnetic resonance spectroscopy ((1)H MRS) to assess IHL, and whole abdominal CT scanning (from the top of the liver to the floor of the pelvic cavity = about 700 slices) to determine the total abdominal subcutaneous fat volume (SFV) and VFV. Seven subjects from the original population were placed on a diet and exercise program, and these indices were examined again after 5% reduction of body weight. Abdominal SFV, VFV, and IHL were mutually independent, but BMI and %-Fat were not independent of the other factors. According to multiple regression analysis, IHL (but not SFV or VFV) was significantly correlated with both HOMA-R and the MATSUDA Index in obese patients. Weight reduction by 5% led to improvement of the MATSUDA Index and decreased the number of subjects with metabolic syndrome, and the reduction of IHL was greater than that of SFV or VFV. These results suggest that IHL may be a superior marker of insulin resistance.