Exercise Training Rapidly Increases Hepatic Insulin Extraction in NAFLD

Purpose We aimed to determine the immediacy of exercise intervention on liver-specific metabolic processes in nonalcoholic fatty liver disease. Methods We undertook a short-term (7-d) exercise training study (60 min.d(-1) treadmill walking at 80%-85% of maximal heart rate) in obese adults (N= 13, 58 +/- 3 yr, 34.3 +/- 1.1 kg.m(-2), >5% hepatic lipid by(1)H-magnetic resonance spectroscopy). Insulin sensitivity index was estimated by oral glucose tolerance test using the Soonthorpun model. Hepatic insulin extraction (HIE) was calculated as the molar difference in area under the curve (AUC) for insulin and C-peptide (HIE = 1 - (AUC(Insulin)/AUC(C-Pep))). Results The increases in HIE, (V) over dotO(2max), and insulin sensitivity index after the intervention were 9.8%, 9.8%, and 34%, respectively (all,P< 0.05). Basal fat oxidation increased (pre: 47 +/- 6 mg.min(-1)vs post: 65 +/- 6 mg.min(-1),P< 0.05) and carbohydrate oxidation decreased (pre: 160 +/- 20 mg.min(-1)vs post: 112 +/- 15 mg.min(-1),P< 0.05) with exercise training. After the intervention, HIE correlated positively with adiponectin (r= 0.56,P< 0.05) and negatively with TNF-alpha (r= -0.78,P< 0.001). Conclusions By increasing HIE along with peripheral insulin sensitivity, aerobic exercise training rapidly reverses some of the underlying physiological mechanisms associated with nonalcoholic fatty liver disease, in a weight loss-independent manner. This reversal could potentially act through adipokine-related pathways.