Synergistic Preventive Effect of Aerobic and Resistance Exercises on Nonalcoholic Fatty Liver Disease (original) (raw)

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Ju-Yeon Cho1 , Won Sohn2

1Department of Internal Medicine, Chosun University College of Medicine, Gwangju, and 2Division of Gastroenterology, Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Nonalcoholic fatty liver disease (NAFLD) is defined as the presence of excessive fat in the liver without significant alcohol consumption. NAFLD is closely associated with metabolic disorders such as obesity, hypertension, dyslipidemia, and diabetes mellitus. The burden of NAFLD is increasing worldwide. The global prevalence of NAFLD has increased over time, from 26% in studies from 2005 or earlier to 38% in studies from 2016 or beyond.1 NAFLD management is important because it can increase the risk of cardiovascular diseases, overweight/obesity-related cancers, and liver-related outcomes, such as cirrhosis or hepatocellular carcinoma.2

The mainstay of NAFLD treatment is weight reduction through lifestyle modification. Weight loss of 5% improves hepatic steatosis and insulin resistance, whereas >7% weight reduction is associated with an improvement in histological steatohepatitis. Lifestyle modifications in NAFLD treatment primarily involve diet and exercise. A meta-analysis showed that exercise reduced only intrahepatic fat in patients with NAFLD.3 Whether aerobic physical activity or resistance exercise is effective in NAFLD treatment is debatable. Magnetic resonance spectroscopy revealed that both aerobic physical activity and resistance exercise significantly reduced intrahepatic fat.4 A meta-analysis revealed no significant difference in the improvement of hepatic steatosis between aerobic physical activity and resistance exercise.5

It is unclear whether aerobic physical activity and resistance exercise have a synergistic effect on the improvement of NAFLD. In this issue of Gut and Liver, Yang et al.6 investigated the synergistic effect of aerobic and resistance exercises on fatty liver in Korean individuals. The authors showed that the prevalence of NAFLD was negatively associated with intensive physical activity and frequent resistance exercise. Moreover, this study revealed that the combination of aerobic physical activity and resistance exercise was associated with a reduced risk of NAFLD. The prevalence of NAFLD in individuals undertaking highly active physical activity and resistance exercise ≥5 days/week was significantly lower than that in those who were physically inactive and performed resistance exercises 0–1 day/week (odds ratio: 0.64 and 0.28 in men and women, respectively).6

The present study6 had some limitations. First, hepatic steatosis was defined based on a simple blood test using the NAFLD fat score. The accuracy of the NAFLD fat score in the diagnosis of fatty liver is not high compared to that of imaging studies such as ultrasonography or magnetic resonance-based tests. Second, this study did not investigate the relationship between exercise and liver fibrosis in patients with NAFLD because of the lack of diagnostic tests for liver fibrosis. It is well known that the stage of liver fibrosis is the most important factor in predicting the prognosis of NAFLD. Advanced fibrosis or cirrhosis is an independent risk factor for liver-related events, cardiovascular diseases, obesity-related malignancies, and all-cause mortality.7 A previous study based on liver histology showed that the risk of nonalcoholic steatohepatitis and advanced fibrosis was decreased in patients who undertook vigorous-intensity exercise but not in those who undertook moderate-intensity exercise.8 Third, there was a lack of information on diet and calorie restrictions in the present study. Calorie restriction is a crucial lifestyle modification for the management of NAFLD. Previous studies have revealed that exercise can only reduce intrahepatic fat but not decrease lobular inflammation, hepatocyte ballooning, and liver fibrosis in patients with NAFLD.9 Weight reduction by calorie restriction and exercise results in the reduction of intrahepatic fat and regression of steatohepatitis and liver fibrosis in patients with NAFLD.10 Finally, the causal inference in this study was relatively weak because it was a cross-sectional study. Despite these limitations, this study is important for a better understanding of the effect of exercise in patients with NAFLD. Particularly, the synergistic effects of aerobic physical activity and resistance exercise on reducing the risk of NAFLD. Further prospective studies are needed to clarify the aforementioned issues regarding the role of exercise in NAFLD management.

CONFLICTS OF INTEREST

No potential conflict of interest relevant to this article was reported.

References

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