## 4 Discussion
The term height\({}^{2}/\)R is then modeled to approximate the real geometry of the human body by a coefficient, depending on a number of factors. Therefore, variations in the height-to-conductive length ratio or in the shape of the body can lead to errors in body composition measurement [15]. Further differences can be found in the estimation in subjects with central obesity, where a higher proportion of visceral fat is concentrated in the abdomen, between the internal organs and torso. In comparison, subjects without abdominal obesity have fat distributed more widely; it is located subcutaneously and is interspersed in the skeletal muscle [2]. This study explored whether the different fat distribution pattern in subjects with central obesity can affect BIA's accuracy. We have shown that the differences between the %BF measured by the two body composition techniques are statistically significant in both subgroups--with and without central obesity. However, the values of the bias are close to each other and similar to the bias for the entire group. In addition, for the subjects with the higher WHtR (above 0.5), we confirmed the assumption that the trunk's contribution to the whole body impedance is small, due to its relatively short length in comparison to the limbs and to its large cross-sectional area [42]. Comparable results were obtained when the study group was stratified by the obesity criteria defined by the WHO classification or to the one of the International Diabetes Federation (the results are provided in the Supplementary Materials). However, the bias reached 3.99 \(\pm\) 5.1% and 4.353 \(\pm\) 4.59%, respectively. In the present study, the bias seen in the two groups, with and without abdominal obesity, was comparable, and so BIA can be regarded as an acceptable method to assess body composition changes in patients with central obesity in longitudinal studies. Since it is a widely accessible and easy to use method, it can be considered a useful tool for obesity clinicians and healthcare professionals in assessing %BF during their standard clinical practice. However, since BIA's reliability is influenced by multiple factors, further research would be helpful to further investigate the method. A major strength of the present study was the heterogeneity of the study group, with a wide spread of ages and a balanced gender distribution. The same applied to the anthropometric characteristics, about half of the subjects being overweight or obese. This enabled us to compare the assessment methods in both genders and to stratify the study group according to the BMI or central obesity criteria. The study has several limitations. One of them is that the software of the device used for the BIA measurements (Maltron BioScan 920-2, Maltron International Ltd., Essex, UK) does not mention the formula it employs to transform the raw bioelectrical parameters into body mass components. This represents a more widespread drawback often associated with BIA measurement; it can be unclear which algorithms are used by each manufacturer within in each product type. Although the size of the study group was large enough to enable statistical significance, a larger sample would have allowed a more detailed stratification and more in-depth conclusions. Further research can be performed in this direction. The present results make reference only to an Eastern European Caucasian population. Applying this direction of research in other ethnic groups might be a subject of interest. Further research is also needed to investigate the impact of the differences between the two body composition methods in longitudinal follow-up studies, especially since the highest bias was observed in subjects with a normal BMI.