The Impact of Body Composition on the Prognosis of Nonalcoholic Fatty Liver Disease (original) (raw)

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Editorial

Do Seon Song

Department of Internal Medicine, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, 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.

Body

In recent years, as the number of patients with obesity and type 2 diabetes has increased worldwide, nonalcoholic fatty liver disease (NAFLD) has become the most common cause of chronic liver disease.1 NAFLD is associated with not only liver-related complications but also an increased risk of cardiovascular events and nonhepatic cancer.2,3 Moreover, the NAFLD-related mortality is associated with hepatic fibrosis stage.3

NAFLD is closely associated with obesity. NAFLD is more prevalent in obese individuals, and obesity is a risk factor for severe NAFLD.4 Body mass index (BMI) is usually used to diagnose obesity (BMI ≥30 kg/m2 according to the World Health Organization definition and BMI ≥25 kg/m2 according to the World Health Organization Asian-Pacific definition). BMI reflects total body fat content, but it does not reflect the distribution of body fat because it cannot differentiate muscle mass from fat mass and cannot discriminate between visceral and subcutaneous fat. In addition, lean NAFLD patients with a normal BMI are less likely to be obese. Therefore, the number of studies on the effect of body composition on NAFLD have been increasing.

The important body components associated with NAFLD are visceral fat and skeletal muscle mass. Visceral adipose tissue, which is associated with metabolic dysregulation, is a key contributor to the inflammatory response that plays a role in the progression of NAFLD to nonalcoholic steatohepatitis. Because sarcopenia and NAFLD share a common pathophysiology, sarcopenia is common in patients with NAFLD. Sarcopenia is significantly associated with hepatic inflammation and fibrosis in patients with NAFLD.5

In the last issue of the Gut and Liver, Han et al.6 reported an association between the ratio of appendicular skeletal muscle mass to visceral fat area (SV ratio) and hepatic comorbidities, such as hepatic steatosis and fibrosis. Individuals with the lowest SV ratio had 3.11-fold and 2.44-fold greater risks of NAFLD among those with and without sarcopenia, respectively (all p<0.05). Only the patient group with both the lowest SV ratio and sarcopenia showed a significant increase in the risk of significant fibrosis (odds ratio [OR], 4.15; p=0.003), while neither the lowest SV ratio alone (OR, 1.17; p=0.505) nor sarcopenia alone (OR, 1.68; p=0.324) were shown to increase the risk of significant fibrosis after adjusting for multiple metabolic risk factors. In addition, atherosclerotic cardiovascular disease risk was significantly greater in those with both the lowest SV ratio and sarcopenia (OR, 2.66; p=0.025), while no such increase was observed in the other individuals (all p>0.05). These results indicate that assessing body composition in NAFLD patients may help identify patients at high risk of advanced hepatic fibrosis as well as those predisposed to cardiovascular events.

However, the results of this study should be interpreted with caution due to several limitations. First, hepatic steatosis and fibrosis were diagnosed by noninvasive imaging methods such as controlled attenuation parameters and transient liver elastography rather than by histologic methods. Although the accuracy of noninvasive imaging assessment for steatosis and fibrosis has increased, histologic diagnosis is currently the gold standard.7 Second, muscle strength and quality, typically evaluated by handgrip strength and the degree of myosteatosis, were not assessed. Previous studies have shown that myosteatosis, as well as sarcopenia, is associated with NAFLD in lean individuals and the progression of hepatic fibrosis.8 In addition, muscle strength is also associated with advanced hepatic fibrosis in individuals with NAFLD.9 Third, this study employed an atherosclerotic cardiovascular disease risk score rather than actual cardiovascular events. The risk score may not be appropriate for individuals of Asian ethnicity due to its development in the United States. In addition, the risk score may not accurately predict the incidence of events because it fails to encompass all relevant risk factors and their dynamic changes over time. Fourth, this study revealed changes in liver stiffness in some individuals, with a median time difference of 11 months, which is too short a time to observe significant changes. A meta-analysis of biopsy-based studies revealed that the duration of stage 1 fibrosis progression was 14.3 years in NAFLD patients and 7.1 years in those with nonalcoholic steatohepatitis.10 Long-term prospective studies are required to examine the associations between changes in body composition and liver fibrosis and the incidence of cardiovascular events.

CONFLICTS OF INTEREST

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

References

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