*2.1. Sample Description*

The data for this cross-sectional analysis came from the Children's Health InterventionaL TriaL (CHILT) III. CHILT III is an 11-month, family-based, multi-component program for obesity prevention and therapy, registered in the German Clinical Trials Register under ID DRKS00026785. It was launched in 2003 at the German Sport University, Cologne. The target groups were children and adolescents aged 8–16 years with obesity or overweight if displaying cardiovascular risk factors, such as arterial hypertension or hyperlipoproteinemia [25].

The minimum criteria for inclusion in this study were participation in the CHILT III program between 2003 and 2020; complete height, weight, age, and body fat percentage data at baseline; and fully completed HRQOL and/or self-concept questionnaires. After excluding extreme values, a final data set of 241 children and adolescents (51.9% girls) and their parents (*n* = 459: 236 mothers, 223 fathers) remained (see Figure 1).

**Figure 1.** Flow Chart of Number of Participants in the Study; HRQOL, Health-Related Quality of Life; CHILT, Children's Health InterventionaL Trial; ° subdomains of self-concept; vertical arrows, stepwise procedure of the study; horizontal arrows, stepwise exclusion criteria **Figure 1.** Flow Chart of Number of Participants in the Study; HRQOL, Health-Related Quality of Life; CHILT, Children's Health InterventionaL Trial; ◦ subdomains of self-concept; vertical arrows, stepwise procedure of the study; horizontal arrows, stepwise exclusion criteria.

### *2.2. Anthropometric Data 2.2. Anthropometric Data*

Standard calibrated scales and stadiometers were used to measure and weigh each child. Height and weight were measured with the child barefoot. Weight included clothing, such as light sportswear. BMI (weight (kg)/height2 (m2)) was assessed and sex- and age-specific weight-for-height BMI Z-scores were calculated according to the German percentile graphs of Kromeyer-Hauschild et al. [26] using the following equation: Standard calibrated scales and stadiometers were used to measure and weigh each child. Height and weight were measured with the child barefoot. Weight included clothing, such as light sportswear. BMI (weight (kg)/height<sup>2</sup> (m<sup>2</sup> )) was assessed and sex- and agespecific weight-for-height BMI *Z*-scores were calculated according to the German percentile graphs of Kromeyer-Hauschild et al. [26] using the following equation:

### (BMI/M(t))L(t)-1)/(L(t) × S(t)), (BMI/M(t))L(t)-1)/(L(t) × S(t)),

where M(t), L(t) and S(t) reflect age- and gender-specific parameters of the child. Children were then categorized as overweight (>90th percentile and ≤97th percentile) or obese (>97th percentile). Body composition was determined by measuring skin-fold thickness to the nearest 0.2 mm in triplicate at the triceps (tric) and subscapula (subs) with a body fat caliper (Harpender Skinfold Caliper HSK-BI, British Indicators, West Sussex, England) following a standardized protocol [27]. The mean of the three measures was considered the final value. When tric+subsc was >35 mm (*n* = 230) the following sex- and age-specific equations by Slaughter (1988) [28] were used to compute the body fat percentage, as these where M(t), L(t) and S(t) reflect age- and gender-specific parameters of the child. Children were then categorized as overweight (>90th percentile and ≤97th percentile) or obese (>97th percentile). Body composition was determined by measuring skin-fold thickness to the nearest 0.2 mm in triplicate at the triceps (tric) and subscapula (subs) with a body fat caliper (Harpender Skinfold Caliper HSK-BI, British Indicators, West Sussex, England) following a standardized protocol [27]. The mean of the three measures was considered the final value. When tric+subsc was >35 mm (*n* = 230) the following sex- and age-specific

had also been used during previous studies on similar populations [29]:

equations by Slaughter (1988) [28] were used to compute the body fat percentage, as these had also been used during previous studies on similar populations [29]:

$$\text{Girls}\_{\prime}\% \text{fat} = 0.546 \times \text{(sum of tric and subs)} + 9.7$$

$$\text{Boys, } \% \text{fat} = 0.783 \times \text{(sum of tric and subs)} - 1.7$$

When tric + subsc was ≤35 mm (*n* = 11), Slaughter's fat-percentage equations were used according to Rodrígez et al. 2005 [30].
