Positive Effects of Exercise Intervention without Weight Loss and Dietary Changes in NAFLD-Related Clinical Parameters: A Systematic Review and Meta-Analysis

Abstract

One of the focuses of non-alcoholic fatty liver disease (NAFLD) treatment is exercise. Randomized controlled trials investigating the effects of exercise without dietary changes on NAFLD-related clinical parameters (liver parameters, lipid metabolism, glucose metabolism, gut microbiota, and metabolites) were screened using the PubMed, Scopus, Web of Science, and Cochrane databases on 13 February 2020. Meta-analyses were performed on 10 studies with 316 individuals who had NAFLD across three exercise regimens: aerobic exercise, resistance training, and a combination of both. No studies investigating the role of gut microbiota and exercise in NAFLD were found. A quality assessment via the (RoB)2 tool was conducted and potential publication bias, statistical outliers, and influential cases were identified. Overall, exercise without significant weight loss significantly reduced the intrahepatic lipid (IHL) content (SMD: −0.76, 95% CI: −1.04, −0.48) and concentrations of alanine aminotransaminase (ALT) (SMD: −0.52, 95% CI: −0.90, −0.14), aspartate aminotransaminase (AST) (SMD: −0.68, 95% CI: −1.21, −0.15), low-density lipoprotein cholesterol (SMD: −0.34, 95% CI: −0.66, −0.02), and triglycerides (TG) (SMD: −0.59, 95% CI: −1.16, −0.02). The concentrations of high-density lipoprotein cholesterol, total cholesterol (TC), fasting glucose, fasting insulin, and glycated hemoglobin were non-significantly altered. Aerobic exercise alone significantly reduced IHL, ALT, and AST; resistance training alone significantly reduced TC and TG; a combination of both exercise types significantly reduced IHL. To conclude, exercise overall likely had a beneficial effect on alleviating NAFLD without significant weight loss. The study was registered at PROSPERO: CRD42020221168 and funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 813781.

Benefits of Physical Exercise as Approach to Prevention and Reversion of Non-Alcoholic Fatty Liver Disease in Children and Adolescents with Obesity

“…Exercise is beneficial both in the prevention and in the treatment of NAFLD in adulthood, aside from dietary changes and independently from weight loss [ 142 , 143 ]. Indeed, it has been shown that hepatic steatosis prevalence is significantly lower in physically active men who regularly exercise (≥2–3 days per week) with respect to men with sedentary lifestyle [ 140 ].…”

Effects of exercise on NAFLD using non-targeted metabolomics in adipose tissue, plasma, urine, and stool

“…Clinical studies focusing on physical exercise interventions have shown that exercise decreases weight, waist circumference, body fat, and blood pressure in NAFLD patients 5 . Moreover, clinical parameters of NAFLD, such as intrahepatic lipid content (IHL), insulin sensitivity, and liver enzymes such as alanine aminotransaminase (ALT) and aspartate aminotransaminase (AST) have also been improved with physical exercise 6 – 10 . Furthermore, changes in the levels of endogenous and gut-microbiota produced metabolites including purine, tryptophan, carnitine, and steroid metabolites induced by physical exercise may be partially responsible for the exercise-related health benefits 11 , 12 .…”

Nonalcoholic Fatty Liver Disease and Cardiovascular Disease: a Review of Shared Cardiometabolic Risk Factors

“…A multitude of studies have demonstrated that total sitting time and physical inactivity were independently associated with NAFLD in a dose-dependent manner, while physical activity reduced both the odds of developing NAFLD and the intrahepatic lipid content in NAFLD patients independently of weight loss. 26,27…”

“…[21][22][23][24][25] A multitude of studies have demonstrated that total sitting time and physical inactivity were independently associated with NAFLD in a dose-dependent manner, while physical activity reduced both the odds of developing NAFLD and the intrahepatic lipid content in NAFLD patients independently of weight loss. 26,27 Active and passive smoking are associated with increased risk of NAFLD development and NAFLDrelated mortality, with a more prominent effect on women, while smoking cessation can improve NAFLD. [28][29][30] Furthermore, body mass index (BMI) and active smoking may have a synergistic effect increasing the odds ratio for NAFLD >8-fold.…”