Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in children [1]. It encompasses a spectrum of liver diseases ranging from fatty liver alone to the triad of fatty infiltration, inflammation, and fibrosis, termed nonalcoholic steatohepatitis. Early detection of NAFLD is important, and the disease can be screened using risk factors, including obesity, hypertriglyceridemia, and insulin resistance. Since it is strongly associated with obesity, NAFLD prevalence is increasing with that of obesity due to changes in lifestyle and diet patterns [2,3]. Body mass index (BMI) has been used widely as a marker of adiposity [4]; however, use of BMI to identify excess body adiposity has poor sensitivity because it cannot differentiate body fat from lean mass [5]. Meanwhile, sarcopenic obesity is closely associated with chronic diseases [6]. The term sarcopenia comes from the Greek words sarx (meaning flesh) and penia (meaning loss). The definition of sarcopenic obesity necessarily combines those of sarcopenia and obesity, describing those who have low muscle mass with a relatively high proportion of fat mass (FM) [7]. In this paper, we suggest considering BMI and percent body fat (PBF) simultaneously to reflect body adiposity and identify at-risk patients for obesity-related disease. Furthermore, we plotted the body composition indices of NAFLD patients in a chart and visualized the distribution of patient body composition. We also divided the patient group based on values of PBF and BMI and sorted them into zones to compare patient characteristics.

The mean age of the population of 38 boys was 13.0±2.3-years. The mean BMI and BMIZ were 28.2±4.0 and 1.85±0.68, respectively. Mean PBF was 39.9%±5.5% (Table 1).

We expressed the body composition indices of subgroups using the body composition chart with FFMI on the x-axis and FMI on the y-axis. BMI of 23 kg/m² and PBF of 30%, corresponding approximately to the 85th percentile for 13-yearold boys [15], were chosen as reference lines on the chart, as the mean age of this study group was 13. The plane was divided into zones A–D by the reference lines (Fig. 1). Thirty-four boys showed BMI over 23 kg/m², and 37 boys showed PBF over 30%. Thirty-three boys were located in zone C, indicating that a large percentage of NAFLD patients has both high BMI and PBF. Four boys were located in zone D, which represents sarcopenic obesity. The boy in zone B was 16 years old with a BMI of 29.3 kg/m², 95th–97th percentile, and PBF of 26.5%, 75th–85th percentile, probably indicating a muscular body (Table 2).

Furthermore, we compared the biochemical profiles and body composition indices between boys in zones C and D. Boys in zone C had higher WTZ, BMIZ, FM, FMI, FFM, and FFMI values than those of zone D (P<0.05). The difference in ALT between the 2 groups was not significant (Table 3).

In the correlation analysis between biochemical profiles and body composition indices, ALT level was positively correlated with BMIZ, PBF, and FMI. The correlation coefficients of ALT with PBF, BMIZ, and FMI were 0.498 (P<0.005), 0.326 (P<0.005), and 0.433 (P<0.005), respectively (Table 4).

NAFLD is usually asymptomatic and requires screening for detection. No screening guidelines exist outside of weight categorization (BMI ≥85th percentile for age and sex) [16]. However, screening the risk population only by BMI has limitations. There is a considerable number of NAFLD patients who maintain a weight lower than the 85th percentile for age and sex, and they usually have a large FM proportion, showing high PBF. Low muscle mass, representing sarcopenic obesity, is associated with metabolic risk, and muscular strength is positively related to higher insulin sensitivity in children and adolescents [17-19]. Early detection of sarcopenic obesity in childhood will help prevent obesity-related metabolic diseases.

In this study, although most of the NAFLD patients were located in zone C, with both high BMI and PBF, 4 NAFLD boys were located in zone D and might not have been identified by a screening test considering only BMI. Furthermore, one NAFLD patient was located in zone B, showing BMI≥85th percentile but PBF<85th percentile, suggesting similar limitation to considering only PBF. This study implies that screening for obesity-related disease using both BMI and PBF can increase detection sensitivity. In addition, dividing body composition chart into zones could be practical at an individual person level.

Recently, new normative standards were proposed for ALT concentration (≤25 U/L for boys and ≤22 U/L for girls) [20]. Higher ALT level suggests a more advanced stage of NAFLD, hepatitis, or fibrotic changes [21]. Thus, even though ALT elevation underestimates liver injury in NAFLD, it is still an easily available screening tool for clinicians to use when assessing children and adolescents who are overweight or obese [22]. In this study, 37 of 38 NALFD patients had ALT above the normal value (>25 U/L). Furthermore, ALT showed positive correlation with BMIZ, PBF and FMI, meaning that the more obese is the patient, the more likely it is that severe liver disease is present.

BMI is an indicator of adiposity; however, both FMI and FFMI affect BMI, preventing differentiation of body fat from lean mass using BMI alone [5]. We suggest using body composition indices in evaluating obesity, which is a significant risk factor of many diseases, including NAFLD. It is important to monitor proper accretion of lean body mass including bone mineral content in children and adolescents during growth. Presenting the body composition indices using a graph and visualizing where the child is located can arouse the attention of both patient and clinician.

In this study, BIA was used for body composition analysis instead of dual-energy X-ray absorptiometry (DXA), which is often used in research and is considered the standard. BIA was used because it is a simple, easy, and time-saving technique that avoids radiation exposure and shows high correlation with other methods of obesity assessment, such as DXA and CT [23,24].

There are some limitations to the study. A small group of 38 NAFLD patients was involved, and only boys were considered. A larger study considering both boys and girls should be performed in the future. In addition, waist circumference, which is a well-known risk factor of obesity-related disease, was not included among variables in this study due to the limited data.

Dividing the chart by single lines of BMI and PBF has limitations, because BMI and PBF are age- and sex-dependent, and increases in growth during the adolescent period are accompanied by increases in BMI and FFMI [15]. Plotting charts for each age subgroup or age-specific assessment at the individual level should be performed to overcome this limitation.

Looking closer at the three 10-year-old boys located in zone D, BMI of all 3 is below the 85th percentile, but the one boy with PBF 31.3% is in the 50th–75th percentile (Table 2). When dividing the chart by reference values for a 10-year-old boy, this boy is located in zone A; however, since his PBF is greater than 30%, he could be considered to have high PBF and needs to be carefully evaluated. In a study of children and adolescents aged 5 to 18 years, PBF above 25% in males and 30% in females has been reported as a significant risk factor of cardiovascular disease (CVD) [25]. Overweight children and adolescents with increased CVD risk need to be evaluated according to PBF percentile subgroup even with PBF below the 85th percentile.

In conclusion, we suggest considering both BMI and PBF to reflect body adiposity and detect those at risk of obesity-related disease such as NAFLD. Body composition zones on a body composition chart might be a useful screening tool in risk assessment, especially in sarcopenic obese children.