Body Composition in Children: What Does It Tell Us So Far?

The Special Issue "Body Composition in Children" of the journal "CHILDREN" aimed to publish both original and review articles focusing on the prevalence and determinants of obesity across childhood, the role of body composition in children's health, new approaches to assessing body composition, and interventions aiming to improve body composition in children and adolescents [...].

The Special Issue "Body Composition in Children" of the journal "CHILDREN" aimed to publish both original and review articles focusing on the prevalence and determinants of obesity across childhood, the role of body composition in children's health, new approaches to assessing body composition, and interventions aiming to improve body composition in children and adolescents.
Body composition plays an important role in children's health and influences their energy requirements. It is determined by several factors, including genetic predisposition, age, gender, ethnicity, perinatal factors, energy balance (nutrition, physical activity, and sedentary behavior), and health status, while it can be assessed using various complex techniques (e.g., the four-compartment model) or more surrogate methods (anthropometry, bioelectrical impedance analysis (BIA), etc.). Developing new tools, standardizing the assessment methods, and evaluating the validity and applicability of existing or novel methods of assessing body composition in pediatric populations would help to optimize nutritional assessment and enable the scientific community to overcome important barriers related to its applicability in public health actions and in clinical practice.
Furthermore, understanding the underlying mechanisms linking body composition and health is essential. Studies exploring the pathways through which adiposity induces changes in health indices are required in order to tackle the effects of obesity on children's metabolic profile and quality of life, and on the development of chronic diseases across the lifespan. On the other hand, exploring the effectiveness of lifestyle interventions in improving children's body composition is essential for the prevention of obesity.
To shed further light on this field, fifteen articles following different designs and methodologies were included in the present Special Issue, and their major findings are given in Table 1.
The cross-sectional study by Markovic et al. reported prospective changes in the prevalence of obesity within a national representative sample of primary schoolchildren (n = 6105) in Serbia [1]. Data were collected in 2015 and 2019, and the children were categorized according to the International Obesity Task Force (IOTF) and the WHO criteria. The results of this study showed that the prevalence of overweight/obesity increased by 4.1% based on the WHO criteria, or by 7.2% based on the IOTF criteria, indicating that the monitoring and surveillance of pediatric malnutrition should be included in Serbia's public health agenda. • 18.7% of children and 24.5% of adolescents had >10% of their total energy intake from added sugars.

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The main sources of added sugars in both age groups were sweets (29.8%) and processed/refined grains and cereals (19.1%).

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In adolescents, the third main contributor was sugar-sweetened beverages (20.6%). • Children/adolescents with >10% of their total energy intake from added sugars were more likely to be overweight or obese compared to their peers with <10% of their total energy intake from added sugars.

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The predicted probability of becoming obese was also significant with higher total and added sugar consumption.

Cross-sectional study
Tanner stage assessment of body posture (Zebris system). Body composition analysis (TANITA MC 780 MA): measurement of body weight, adiposity, lean mass, muscle mass, total body water, BMR, compartmental body composition analysis. Measurement of body height Calculation of BMI.

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Pelvic obliquity was lower in older children.

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Age played a significant role in differences in the height of the right pelvis, and the difference in the height of the right shoulder.

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The content of adipose tissue (FAT%) increased with BMI and decreased with increasing weight, age, and height. • FAT% was lower in boys compared to girls.

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Older children (puberty) had greater asymmetry in the right shoulder blade and right shoulder.

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Younger children (who were still prepubescent) had greater anomalies in the left trunk inclination as well as in the pelvic obliquity. • Girls in puberty were characterized by greater asymmetry on the right side, including the shoulders, the scapula, and the pelvis.

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In boys, the problem related only to the asymmetry of the shoulder blades. • Girls were characterized by a greater increase in adipose tissue and boys by muscle tissue. • Significant differences appeared in children's body posture.

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Greater asymmetry within the scapulas and shoulders were seen in children during puberty. The greatest variability was found in the 11-year-old group, with an increase of 5.5 cm for males and 5.4 cm for females. • The weekly volume of training was higher in the group of swimmers than in that playing other sports.

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After 12 weeks of training, body height and weight increased in both groups. However, the BMI value and adipose tissue content only increased in the group of non-swimmers. • Swimmers perceived greater exertion during training than non-swimmers. • A significant interaction between groups (intervention vs. control) and time (pre-vs. post) was observed for weight and BMI. • Significant main effect of time was found for body fat (kg) and body fat (%).

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The results of the current study show that a 12-week after-school volleyball program, including 2 session/week, can improve body composition in overweight adolescent girls.
Georgiou et al. conducted a cross-sectional study to record the nutritional habits and to explore the level of adherence to the Greek food-based guidelines among children and adolescents classed as overweight or obese (n = 1467, 2-18 years old) [2]. According to the findings of this study, the consumption of various core food groups (dairy products, fruit, vegetables, legumes, and fish) was lower than the national recommendations, while the consumption of meat/poultry exceeded them. Moreover, a high number of the participants were found to consume unhealthy foods and beverages (e.g., regular soft drinks, sweets, salty snacks, etc.) regularly. The findings of this study indicate that a large proportion of overweight/obese children and adolescents in Greece do not adhere to the national food-based recommendations; therefore, public health initiatives must be carried out to improve their dietary habits and prevent further increases in their body weights.
The studies by Magriplis et al., Karatzi et al., and Ferrer-Santos et al. aimed to provide more evidence regarding the determinants of obesity in children and adolescents [3][4][5]. More specifically, Magriplis et al. conducted a cross-sectional study to record sugar intake in Greek children and adolescents and to explore its association with overweight/obesity [3]. The study sample included 1165 children/adolescents aged ≥ 2-18 years, who participated in the Hellenic National Nutrition and Health Survey (HNNHS). According to the results of this study, a large proportion of the participants (18.7% of children and 24.5% of adolescents) exceeded the recommendation of 10% of total energy intake from added sugars, which may be attributed to their high consumption of foods rich in sugar, such as sweets and processed/refined grains and cereals in the case of children, or sugar-sweetened beverages in the case of adolescents. Furthermore, individuals with an intake of ≥10% of their total energy from added sugars were more likely to be overweight/obese compared to their peers with an intake of <10%, even after adjusting for the intake of other foods or macronutrients. In their systematic review, Karatzi and her colleagues explored the impact of the COVID-19 pandemic on children's and adolescents' lifestyles and cardiovascular risk factors [4]. The electronic search resulted in 15 studies, which met the eligibility criteria set by the authors. It was revealed that the prolonged measures taken to fight against the COVID-19 pandemic had negative effects on children's and adolescents' dietary and lifestyle behaviors (e.g., an increase in the consumption of fats, fast-foods, processed foods, sweet and salty snacks, and sugar-sweetened beverages, as well as an increase in screen-time and a decrease in physical activity). However, on the other hand, a few studies also reported some improvements (e.g., an increase in the frequency of breakfast consumption and in fruit and vegetable intake, and a decrease in soft drinks consumption). Such differences could be attributed to the different lockdown periods addressed by each study and the diversity of the measures applied across different countries, as well as the participants' adherence to these measures. This study also reported that the COVID-19 period negatively affected children's and adolescents' weight status and body composition. On the other hand, the more significant presence of parents during the home confinement lead to greater support for type-1 diabetic children, who ultimately achieved better glycemic control. The study by Ferrer-Santos et al. aimed to assess the association between moderate-to-vigorous physical activity (MVPA) and body composition in 308 schoolchildren (aged 7 years old) in Aragon, Spain [5]. Gold standard techniques were used to assess both the participants' body composition (i.e., dual-energy X-ray absorptiometry) and their physical activity (i.e., accelerometers) and included several potential covariates (e.g., lifestyle, body weight gain during the first year of life, parental BMI, smoking status, etc.). Based on the results of this study, MVPA was inversely associated with subtotal and abdominal fat, indicating that the level and intensity of physical activity constitute important determinants of childhood obesity.
Rusek et al. conducted a study based on 464 schoolchildren aged 6-16 years in Poland to examine the alterations in their body composition and posture during puberty growth [6]. The results of this study showed that children with higher BMIs tended to have higher percentages of body fat, while younger children had lower percentages of body fat. Moreover, girls experienced a greater increase in adipose tissue (both in the total and segmental body composition analyses), and boys in lean mass, muscle mass, and total body water. Pubertal status also appeared to influence the children's posture. The findings of this study indicate the necessity of screening children periodically to assess their body composition and posture, and of early intervening, wherever needed, to prevent any adverse consequences of these factors on their health status.
The  [7]. In total, 360 children were recruited from elementary schools in Northern Taiwan. Their body composition was assessed using BIA and their fitness level using different tests and outcomes (800 m run to assess cardiorespiratory fitness; sit-and-reach exercise to assess flexibility; 1 min sit-ups to assess speed/agility; and long-jump to assess lower body power). The findings of this study showed that the % of body fat was independently associated with cardiorespiratory fitness, and the BMI z-score was associated with flexibility. Based on these observations, the authors concluded that weight management and physical fitness should be addressed simultaneously in pediatric populations. Similarly, Tengku et al. conducted a prospective study focusing on the association between the oral disease burden and oral health related quality of life in adolescents, based on their weight status [8]. In total, 195 adolescents classed as overweight/obese and 202 adolescents classed as a normal weight, who were matched by age (14 years at the baseline) and gender, were followed up for two years (2015-2017) in Malaysia. No significant differences were observed between the two groups regarding the burden of oral diseases and indices of oral health related quality of life, thus indicating that obesity in adolescence does not appear to negatively affect these health indices. Jeong et al. compared hematological indices among children and adolescents of different weight categories [9]. The subjects participated in the Korea National Health and Nutrition Examination Survey (KNHANES) in 2007-2018, and, for the purposes of this study, 7997 children/adolescents (4259 boys) were included. The obese participants were found to have higher levels of white blood cells, red blood cells, and platelets compared to their normal-weight peers. Moreover, positive associations were observed between BMI standard deviation scores and white blood cells, red blood cells, hemoglobin, hematocrit, and platelets. As shown in this study, body composition influences hematological parameters and, therefore, children and adolescents with obesity should be periodically screened to assess their levels of these indices. Hsu CN et al. conducted a prospective cohort study based on 63 children and adolescents (8-18 years old) from Taiwan with chronic kidney disease to examine the association of body composition with cardiovascular risk factors [10]. The fat mass index (FMI) z-score was found to be associated with ambulatory blood pressure monitoring, indicating that body composition may influence the levels of certain cardiovascular risk factors and could be considered as a new method for identifying children and adolescents with early-stage chronic kidney disease, who are at a high risk of developing cardiovascular disease.
The studies of Ofenheimer et al., Valencia-Sosa et al., and Thajer et al. focused on the use and utility of certain body composition indicators in healthy or ill children [11][12][13]. In particular, Ofenheimer et al. explored serum lipid profiles in relation to body composition in a large cohort of 1394 children and adolescents (6-<18 years old), who participated in the LEAD study in 2011-2019 [11]. The body composition analysis was performed with dual X-ray absorptiometry (DXA), and the appendicular lean mass (ALMI) and fat mass (FMI) indices were calculated. It was observed that children with high ALMI and high FMI had abnormal levels of certain blood indices, including high levels of triglycerides and LDL cholesterol and low levels of HDL cholesterol. The results of this study also suggest that BMI does not adequately reflect body composition/adiposity. Consequently, more precise methods should be in use to assess body composition and to identify the children who are at a higher risk of developing cardiovascular disease.
Valencia-Sosa et al. provided reference values for neck circumference among Mexican children, a method which was introduced about a decade ago as a new technique for screening for obesity, especially central obesity, and cardiometabolic risk indices in pediatric populations [12]. A number of 1059 schoolchildren aged 6-11 years old with normal weight participated in this study. Overall, the authors recorded an age-dependent increase in the values of neck circumference, as well as a gender-specific difference, since boys had higher values compared to girls. Considering that neck circumference is a valid, simple, low-cost, and easy-to-apply method of screening for obesity and cardiometabolic risk factors, the publication of the percentile reference values for Mexican children is expected to contribute to the early identification of high-risk children and improve public health in Mexico.
Thajer et al. compared different methods of BIA in 123 children and adolescents (6-18 years old) with obesity in Austria [13]. More specifically, two BIA devices, namely TANITA and BIACORPUS, were used to assess body fat in all the study participants, while gold standard techniques (i.e., dual X-ray absorptiometry and air displacement plethysmography) were also applied in a subsample of volunteers. The agreement between the measurements taken by the two BIA methods and the agreement between each BIA method and each gold-standard method were tested using Bland-Altman analyses. The study showed that the BIA methods produced different results in the same individuals, with TANITA overestimating the % of body fat and the fat mass compared to BIACORPUS and underestimating the fat-free mass. Gender-specific differences were also identified. These findings suggest that both BIA devices can be used in clinical practice and research. However, it is important to use the same type of device in order to be able to compare a series of measurements taken at the individual level for clinical assessment and to compare measurements taken by different individuals in population-based studies.
The last two studies by Bielec et al. and Trajkovic et al. examined the impact of physical activity on children's and adolescents' body composition [14,15]. In brief, Bielec et al. compared body composition and anthropometric indices between children 11-12 years old who participated regularly in swimming activities (e.g., football, basketball, athletics, etc.) (n = 46) or other sports, including non-swimming activities (n = 42) for 5-12 h/week over a period of 12 weeks [14]. It was observed that participants' body weights and heights increased in both groups after the 12-week period; however, BMI and body fat percentage increased only among the non-swimmer groups. The authors noted, however, that the group of swimmers engaged in higher volumes of training compared to their non-swimmer peers, which may explain the study findings. It was concluded that the engagement for >10 h/week in vigorous exercise, such as swimming, may prevent excess body fat increase in children.
Trajkovic et al. evaluated the effects of an after-school volleyball program on body composition indices among overweight adolescent girls in Serbia [15]. The participants were randomly allocated to the intervention group (n = 22) or the control group (n = 20) and attended the program for 12 weeks. Both groups followed their standard PE activities, and the intervention group also engaged in small-sided games two times/week. Body composition was analyzed using BIA. The study showed that the after-school volleyball program improved body composition among the intervention group compared to the control group, indicating that it may be a useful strategy for tackling overweight/obesity in adolescent girls.
In conclusion, the studies included in the Special Issue "Body Composition in Children" of the journal "CHILDREN" showed that the prevalence of childhood obesity is increasing in certain areas of Europe. This increase can be attributed, to a large extent, to the adoption of unhealthy dietary and lifestyle behaviors by children and adolescents, which may lead to poor health status and quality of life and pose an economic burden for the public health systems. New methods, such as the neck circumference technique, may be used to identify children/adolescents at a high risk of developing cardiovascular disease and guide them within the health care system so that they can be treated accordingly. In parallel, effective strategies and interventions to promote healthy lifestyles were proposed, and these may be incorporated into future obesity prevention/treatment actions targeting children and adolescents.