The Effect of Exercise Training on Liver Fat and Fibrosis

Non-alcoholic fatty liver disease (NAFLD) is a major health burden, affecting 25% of the global population. NAFLD can progress to non-alcoholic steatohepatitis (NASH), liver cirrhosis, and sometimes liver cancer, and is associated with an increased risk for type-2 diabetes and cardiovascular disease. The fibrosis stage is the strongest histologic predictor for disease-specific and overall mortality or for the need of liver transplantation in patients with NAFLD. Liver biopsy remains the gold standard for histological evaluation of NASH and fibrosis, but its use is limited due to its invasive nature and sampling error. Currently, the most reliable noninvasive method for liver fibrosis diagnosis and quantification is Magnetic Resonance Elastography (MRE). Several studies have reported that a comprehensive lifestyle modification based on reduced energy intake and increased physical activity for 6-12 months induced improvement in liver enzymes and metabolic parameters, reduced liver fat concentrations, and reduced histologic steatosis and necroinflammation. Exercise without weight loss produces a 20-30% relative reduction in liver fat. Different modalities of exercise (aerobic exercise, resistance exercise, or high-intensity intermittent exercise) appear to have similar effects on liver fat. However, most exercise trials to date were small and based on short-term interventions, between 8 and 12 weeks. Even though exercise is recommended as part of the treatment for NAFLD, there have been no large-scale studies to guide healthcare practitioners in prescribing specific exercise programs for the management of NAFLD patients and to promote health among people with obesity and metabolic syndrome.