Habitual physical activity is associated with the intra-hepatic fat content in humans

OBJECTIVE: Fatty liver may be involved in the pathogenesis of type 2 diabetes. Physical exercise is a tool to improve insulin sensitivity, but little is known about its effect on intrahepatic fat (IHF) content. The purpose of this study was to examine the association of habitual physical activity, insulin resistance, and adiponectin with IHF content. RESEARCH DESIGN AND METHODS: Participants were 191 (77 female and 114 male) apparently healthy, nonalcoholic individuals (aged 19-62 years; BMI 17.0-35.5 kg/m2). IHF content was assessed in a quantitative fashion and noninvasively as a continuous variable by means of 1H magnetic resonance spectroscopy (MRS), and habitual physical activity was assessed by means of a questionnaire. Fatty liver was defined as IHF content of >5% wet weight, and insulin sensitivity was estimated using the computer homeostasis model assessment (HOMA)-2 indexes. RESULTS: A reduced prevalence of fatty liver in the quartile of the most physically active individuals (25, 11, 25, and 2% in quartile 1, 2, 3, and 4, respectively; chi2 = 15.63; P = 0.001) was found along with an inverse correlation between the physical activity index and the IHF content when plotted as continuous variables (Pearson's r = -0.27; P < 0.000). This association was not attenuated when adjusted for age, sex, BMI, HOMA-2, and adiponectin (partial correlation r = -0.25; P < 0.001). CONCLUSIONS: This study demonstrated that a higher level of habitual physical activity is associated with a lower IHF content and suggested that this relationship may be due to the effect of exercise per se.