Fat in liver/muscle correlates more strongly with insulin sensitivity in rats than abdominal fat

Intrahepatic or intramuscular lipid (IHL/IML) content has been reported to be correlated with insulin resistance. Visceral fat has also been shown to be associated with insulin resistance. Thus, we investigated whether IHL/IML or visceral fat content is more closely associated with insulin resistance. Twenty Sprague-Dawley rats were divided into two groups based on regular chow diet (RCD) or high-fat diet (HFD; 40% fat). The insulin-sensitivity index (ISI) was determined by euglycemic glucose clamp study, the amount of visceral fat by computed tomography (CT), and the IHL/IML content by magnetic resonance spectroscopy (MRS). Weight, food, and water intake, physical activity, energy expenditure, lipid profile, adiponectin, and high-sensitivity C-reactive protein (hsCRP) levels were measured. At the study end point, visceral fat, and the IHL/IML content were higher in the HFD group than in the RCD group. The IHL/IML content was more highly correlated with ISI than was visceral fat amount. Stronger correlations were also found between adiponectin or hsCRP level and IML/IHL content than visceral fat, especially in the HFD group. Furthermore, the IHL/IML content was significantly associated with the ISI in the multiple regression models but visceral fat was not. There was clear discrimination between RCD and HFD groups in scatter plots of IML/IHL against the ISI, but substantial overlap in that of visceral fat against the ISI. This result suggests that IHL/IML contents are closely related with insulin resistance or atherosclerosis and is a better metabolic index of insulin sensitivity than the visceral fat.