Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition characterized by the accumulation of excess fat in the liver, encompassing a spectrum from simple steatosis to nonalcoholic steatohepatitis and hepatic fibrosis (1, 2). NAFLD has been associated with cardiovascular and metabolic risk factors as well as the development of hepatic cirrhosis and hepatic cancer, even in children and adolescents (1, 3, 4). A meta-analysis revealed a global increase in the prevalence of NAFLD from 4.62% in 2000 to 9.02% in 2017 among children and adolescents (5). Notably, in Korea, the prevalence of NAFLD increased from 45.8% to 62.5% during the outbreak of coronavirus disease 2019 among children and adolescents with obesity (6).

Early screening for NAFLD is crucial for prevention of severe complications, given that NAFLD is often asymptomatic and is reversible with appropriate management during the initial stages (1, 4). Therefore, the Endocrine Society recommends alanine transaminase (ALT) screening for early detection of NAFLD in children with overweight and obesity (7). The North American Society of Pediatric Gastroenterology, Hepatology, and Nutrition recommends imaging studies, including ultrasonography, for NAFLD screening in children with abnormal ALT levels (8).

However, the necessity for blood sampling for ALT screening creates a potential burden on children. Furthermore, some children diagnosed with NAFLD may exhibit normal ALT levels, which can be elevated in various liver-related conditions (1). Consequently, initiatives have been undertaken to explore biomarkers to compensate for the limitations of ALT screening or imaging studies (1, 9). Despite these efforts, additional research in pediatric populations is warranted.

While body mass index (BMI) serves as a diagnostic tool for obesity, individuals whose BMI falls within the normal range may still present a metabolically unhealthy profile commonly associated with obesity; conversely, some individuals who are overweight or obese may be metabolically healthy (10). According to a recent study on the Korean population, the prevalence of metabolically healthy adolescents with overweight or obesity has remained steady, while the number of adolescents with overweight or obesity increased (11). Identifying metabolically healthy individuals with overweight is encumbered by the inherent limitations of BMI measurements, as they lack the ability to distinguish between body fat and muscle mass (12). A meta-analysis reported that bioelectrical impedance analysis (BIA) is a practical method for evaluating body fat in children and adolescents (13). However, investigations on the associations of BIA parameters with pediatric fatty liver disease are limited.

Recently, international experts have released a consensus statement regarding the renaming of fatty liver disease to metabolic dysfunction-associated steatotic liver disease (MASLD) (14). This new terminology reflects the association this condition with hepatic steatosis and the inclusion of at least one out of five cardiometabolic risk factors, which are associated with elements of metabolic syndrome. While this new concept enables the assessment of MASLD as a cardiometabolic risk factor by emphasizing the close pathophysiological link between fatty liver and metabolic dysfunction and insulin resistance, investigations on MASLD in pediatrics are limited. Considering adverse trends in cardiovascular risk factors, including metabolic syndrome, screening strategies for MASLD in pediatric patients are needed (2, 15).

In this study, we aimed to investigate the utility of BIA in identifying different metabolic profiles among individuals who are overweight and obese, providing valuable insights into more effective and less burdensome screening methods for MASLD in the pediatric population. Therefore, our study focused on the development of MASLD-related parameters using anthropometric measurements and BIA parameters that are specifically tailored for children and adolescents who are overweight and obese. Considering the metabolic diversity within this population, our objectives were to (1) examine the associations of BIA parameters with ALT level and MASLD, (2) compare the associations between MASLD and traditional anthropometric data and BIA parameters, and (3) establish valid cutoff values for BIA-related parameters for the prediction of MASLD.

The present study demonstrated that WHR and the combination of BIA parameters with WHR were correlated with ALT level, ALT elevation, and MASLD among youth with overweight and obesity. These relationships were more prominent in the pubertal group. In addition, BIA parameters combined with WHR were stronger predictors than WHR alone. Among the combined parameters, PBF-WHR and VFA-WHR were correlated with the MASLD, even after adjusting for age, sex, and puberty. Moreover, these relationships were significant in youth with normal ALT levels.

In our study, WHR emerged as the sole anthropometric indicator correlated with ALT level in the total population. WHR accounts for both waist and hip measurements, making it a more comprehensive indicator of body fat distribution. The inclusion of hip circumference provides additional information about fat distribution in the lower body, which is relevant because individuals with a higher WHR tend to store more fat in the abdominal area, particularly around the visceral organs, a characteristic feature of individuals at risk for steatotic liver disease (1, 21). Pimenta et al. reported that WHR is strongly correlated with abdominal body fat and body fat distribution (22). A population-based study reported that WHR is a more accurate predictor of severe liver disease than BMI (23). Among anthropometric measurements, including BMI, WC, and WHtR, Zheng et al. reported that WHR was the most powerful predictor of NAFLD in adults (24).

The associations between BIA parameters and pediatric NAFLD have been investigated in several studies. A Japanese study reported that VFA was correlated with NAFLD in children (25). In another Japanese study, magnetic resonance imaging revealed that BIA parameters are associated with total psoas muscle surface area in children with obesity (26). A Chinese study reported that BIA was superior to anthropometric indices in terms of predicting NAFLD among children (27). Based on this evidence, we explored the associations of MASLD with BIA parameters as well as BIA parameters combined with anthropometric measurements. In our study, PBF-WHR and VFA-WHR were associated with MASLD in all subgroups except the prepubertal group, while WHR, SMM/WHR, FMM/WHR, and ASM/WHR were not significantly correlated with MASLD. Therefore, the inclusion of PBF-WHR and VFA-WHR in our study was of significant value for the prediction of MASLD. Choi et al. reported that PBF and the fat mass index are associated with ALT levels, whereas FFM is not (28). The robust relationships between PBF-WHR and VFA-WHR with MASLD can be explained as follows. First, excessive visceral fat accumulation resulting from the infiltration of macrophages among hypertrophied adipocytes is closely associated with the elevation of inflammatory cytokine levels and diminished production of adipokines such as adiponectin (29). A previous study also reported that PBF is closely associated with chronic inflammation in the youth (30). Chronic inflammation plays a crucial role in the development of steatotic liver disease by inducing insulin resistance and promoting the accumulation of lipids in the liver (29). VFA and PBF are linked to insulin resistance and steatotic liver disease via reduced hepatic clearance of insulin (exacerbating hyperinsulinemia), increased production of triglyceride-rich lipoproteins, and elevated hepatic glucose production (31). Notably, examination of the relationship between ALT level elevation and BIA-related parameters revealed that fat-related indicators were significantly associated in boys, while muscle-related indicators were significantly associated in girls. This suggests a potential sex-based difference in the effect of fat and muscle on the occurrence of hepatic fat deposition.

Although ALT is a valuable biomarker, it is not a reliable or accurate predictor of the presence of MASLD (32). Therefore, steatotic liver disease can be underdiagnosed in youth with normal ALT levels, given that the current guidelines recommend imaging studies such as ultrasonography for NAFLD screening, primarily in children with abnormal ALT levels (8). Moreover, a cohort study reported that 14% of patients with NAFLD had normal ALT levels (33). In our study, PBF-WHR and VFA-WHR were correlated with MASLD even in youth with normal ALT levels, whereas WHR alone was not significantly associated with MASLD. These findings suggest that including BIA parameters in the selection criteria for MASLD screening, even in patients with normal ALT levels, could be a beneficial approach for enhancing diagnostic accuracy.

The effectiveness of BIA parameters was notably greater in the pubertal group than in the prepubertal group; our study also revealed significant differences in most BIA parameters between the prepubertal and pubertal groups. This difference can be attributed to the significant changes in body composition, including muscle and fat, that occur during puberty (34). Puberty is a period marked by rapid growth, hormonal changes, and alterations in body composition (35, 36). These changes, including the development of lean muscle mass and the redistribution of fat, can affect the accuracy and relevance of BIA measurements. During puberty, individuals experience substantial growth in muscle mass, which affects BIA-derived measurements (37). Additionally, the redistribution of fat, especially in the abdominal and visceral regions, is characteristic of puberty and influences the parameters related to body fat in BIA. Thus, BIA parameters have become more informative and relevant for assessing metabolic health and risk factors, including steatotic liver disease, in pubertal individuals owing to these dynamic changes in body composition during puberty (36). A longitudinal study reported that the change in energy expenditure during puberty was associated with body composition change (38). The accuracy of BIA in capturing these changes makes it a valuable tool for understanding the associations between body composition and health outcomes during this critical developmental stage.

This study has some limitations. First, our study had a retrospective design and was limited to the Korean population. Second, MASLD was diagnosed using ultrasonography, although biopsy constitutes the gold standard for the diagnosis of steatotic liver disease. Finally, genetic and environmental factors, including nutrition and physical activity, were not considered. However, we propose novel parameters involving the integration of WHR with BIA parameters and show that these parameters are superior to simple anthropometric measurements for the prediction of MASLD even in young patients with normal ALT levels. To the best of our knowledge, this study is the first to experimentally demonstrate the potential of combined parameters using anthropometric data and BIA parameters, indicating the need for more studies with large samples to validate the usefulness of these parameters.

In conclusion, our study demonstrated that BIA parameters combined with WHR exhibited significant correlations with ALT level, ALT elevation, and MASLD and that these relationships were more pronounced in pubertal individuals. The combination of BIA parameters related to fat composition, such as PBF and VFA with WHR, demonstrated stronger associations with MASLD than did WHR alone. Moreover, these relationships were sustained even in youth with normal ALT levels, suggesting the potential of BIA parameters for MASLD screening in such cases. In summary, our study highlights the value of BIA parameters combined with WHR as a promising approach for MASLD screening in youth with overweight and obesity, providing a less burdensome and potentially more effective alternative to traditional methods.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Institutional Review Board of Yonsei University Yongin Severance Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The requirement for informed consent was waived.

KS: Conceptualization, Formal analysis, Investigation, Methodology, Writing – original draft. ES: Data curation, Resources, Writing – review & editing. HY: Formal analysis, Methodology, Writing – review & editing. SJ: Methodology, Writing – review & editing. HS: Methodology, Writing – review & editing. HC: Methodology, Writing – review & editing. E-KK: Methodology, Writing – review & editing. Y-JK: Conceptualization, Formal analysis, Investigation, Methodology, Writing – review & editing. J-WL: Supervision, Writing – review & editing.