Habitual Physical Activity Is Associated With Intrahepatic Fat Content in Humans

Abstract

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/m 2 ). IHF content was assessed in a quantitative fashion and noninvasively as a continuous variable by means of 1 H magnetic resonance spectroscopy (MRS), and habitual physical activity was assessed by means of a questionnaire. Fatty liver was defined as IHF content of Ͼ5% 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; 2 ϭ 15.63; P ϭ 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 ϭ Ϫ0.27; P Ͻ 0.000). This association was not attenuated when adjusted for age, sex, BMI, HOMA-2, and adiponectin (partial correlation r ϭ Ϫ0.25; P Ͻ 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. Diabetes Care 30:683-688, 2007A lanine aminotransferase and ␥-glutamyltransferase are associated with type 2 diabetes risk (1-3), and it is thought that the link is represented by the intrahepatic fat (IHF) content. Ectopic fat accumulation within the liver, in fact, has been reported in association with impairment of insulin-stimulated glucose metabolism, of suppression of endogenous glucose production, and of whole-body lipolysis in nondiabetic individuals with nonalcoholic fatty liver disease (NAFLD) (4,5). Additional results also demonstrated that decreased levels of circulating adiponectin in NAFLD are related to hepatic insulin sensitivity and to the IHF content, suggesting that hypoadiponectinemia may be involved in excessive hepatic fat accumulation (6).Physical exercise was found to be associated with a reduced risk of development of type 2 diabetes (7,8) and is a wellrecognized tool to improve insulin sensitivity at the level of the skeletal muscle (9). However, whether physical exercise may affect insulin sensitivity and diabetes risk via an effect on the IHF content and adiponectin remains unknown.The IHF content may be assessed as a continuous variable by means of 1 H magnetic resonance spectroscopy (MRS) (10), and recently this technique was found to be a sensitive, quantitative, and noninvasive method also when applied to a large population (11) without the need for the use of a more invasive approach such as liver biopsy. The ...

Fatty liver is associated with insulin resistance, risk of coronary heart disease, and early atherosclerosis in a large European population

“…This result is in agreement with previous cross-sectional studies that have shown an association of the level of physical activity with hepatic fat content 22 and with ALT and GGT. 23 Moreover, physical activity has been shown to be associated with a reduced risk to develop T2DM, 24,25 and CVD 26 and exercise is a well-recognized tool to improve insulin sensitivity at the level of the skeletal muscle.…”

Fat distribution in men of different waist girth, fitness level and exercise habit

“…Exercise training prevents steatosis in hyperphagic, obese rats, 33 but physical activity explained only 8% of the variance in liver fat in 191 non-alcoholic men and women. 34 These findings suggest that other factors may influence liver fat content.…”

Fitness versus fatness: Moving beyond weight loss in nonalcoholic fatty liver disease

“…Epidemiologic studies show a negative relationship between NAFLD and selfreported habitual PA levels, [22][23][24][25][26] although this may not persist when adjusted for body weight 23,24 (Table 2). These observations need to be viewed with caution because subjective measures of PA level can be inaccurate and prone to reporter bias.…”