Abstract
Exercise training ameliorates nonalcoholic fatty liver disease (NAFLD) as well as obesity and metabolic syndrome. Although it is difficult to eliminate the effects of body weight reduction and increased energy expenditure—some pleiotropic effects of exercise training—a number of studies involving either aerobic exercise training or resistance training programs showed ameliorations in NAFLD that are independent of the improvements in obesity and insulin resistance. In vivo studies have identified effects of exercise training on the liver, which may help to explain the “direct” or “independent” effect of exercise training on NAFLD. Exercise training increases peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) expression, improves mitochondrial function and leads to reduced hepatic steatosis, inflammation, fibrosis, and tumor genesis. Crosstalk between the liver and adipose tissue, skeletal muscle and the microbiome is also a possible mechanism for the effect of exercise training on NAFLD. Although numerous studies have reported benefits of exercise training on NAFLD, the optimal duration and intensity of exercise for the prevention or treatment of NAFLD have not been established. Maintaining adherence of patients with NAFLD to exercise training regimes is another issue to be resolved. The use of comprehensive analytical approaches to identify biomarkers such as hepatokines that specifically reflect the effect of exercise training on liver functions might help to monitor the effect of exercise on NAFLD, and thereby improve adherence of these patients to exercise training. Exercise training is a robust approach for alleviating the pathogenesis of NAFLD, although further clinical and experimental studies are required.
Highlights
Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease related to obesity and one of the manifestations of metabolic syndrome
Following the development of imaging modalities to evaluate liver steatosis such as 1H magnetic resonance (1HMR), conventional B-mode ultrasonography, and controlled attenuation parameters based on transient elastography, liver steatosis has been used as an endpoint of exercise training in many clinical studies
Of the 39 exercise training protocols we reviewed, four ineffective ones were found, of which three were without significant body weight reduction and all were without dietary consultation (Supplementary Material 2)
Summary
Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease related to obesity and one of the manifestations of metabolic syndrome. Exercise Training in NAFLD with all-cause mortality, and high levels of moderate intensity physical activity eliminate the increased risk of death associated with prolonged sitting times [2]. A number of epidemiological studies have demonstrated a strong correlation between physical activity and non-communicable diseases including diabetes, metabolic syndrome, cardiovascular diseases and cancer [3,4,5,6]. Sitting time was positively correlated with NAFLD prevalence as diagnosed by ultrasonography, independent of body mass index (BMI), in a large crosssectional study [7]. Clinical evidence is analyzed in a systematic review manner and experimental evidence is summarized narratively to evaluate the therapeutic effects and mechanisms of exercise training on NAFLD.
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