Reference data for body composition parameters in normal-weight Polish adolescents: results from the population-based ADOPOLNOR study

Adolescence (10–19 years) is typically a period of robust vitality, marked by peak physical maturity, increased strength, speed, reaction time and improved immune function [1]. Paradoxically, however, this period also coincides with increased susceptibility to nutritional problems. Inadequate nutrition, unhealthy dietary choices, inadequate physical activity and various psychosocial factors such as emotional stressors, body image concerns and societal pressures to conform to beauty ideals exacerbate this vulnerability [2, 3]. Effective strategies, including awareness and surveillance, are essential to address these nutritional disorders [4]. Although BMI is commonly used metric, it has limitations in assessing body fat distribution and hidden deficiencies [5]. As a result, body composition (BC) parameters are more effective in identifying abnormalities such as eating disorders [6], obesity [7], delayed or stunted growth [8], and chronic diseases such as cystic fibrosis, renal disease or inflammatory bowel disease, as well as muscle wasting [9, 10, 11]. Regular assessment using updated reference data is essential for early intervention in the nutritional status of adolescents. Several reference sets have been developed for BC parameters, expressed as age-, sex- and ethnic-specific standard deviations, centile values and growth charts. Recent developments include paediatric reference curves and the corresponding centile values for children aged 8 to 20 years [12]. Data from whole-body dual-energy X-ray absorptiometry (DXA) scans in the National Health and Nutrition Examination Survey (NHANES) provide key measures, including total bone mass density (BMD) and bone mineral content (BMC) [12], as well as fat mass index (FMI) and lean body mass index (LBMI) [13]. In addition, reference centiles for body fat percentage (FM%), FMI and LBMI are now available for different DXA systems such as e Prodigy and iDXA GE Healthcare Lunar systems [14]. Recently published reference values for FM%, FMI and trunk/limb FM assessed by dual-energy X-ray absorptiometry (DXA) are available for a large cohort of Central European children and adolescents aged 6–18 years from the LEAD project [15]. Schmidt and colleagues used bioelectrical impedance analysis (BIA) to ascertain reference values for fat-free mass index (FFMI), fat mass index (FMI), body cell mass index (BCMI), and phase angle (PA) in a nationwide cohort of participants aged 4–24 years in Germany as part of the Motoric Module Study Wave 1 [16]. The study highlighted significant differences in body composition between the representative German sample and the normal-weight sub-sample, emphasising the need for personalised reference values to address specific challenges in adolescent body composition.

Despite the abundance of reference data for body measurements, including body height and weight, BMI, waist and hip circumference and skinfold thickness [17, 18, 19], there is a significant dearth of reliable reference data for complete BC parameters in Polish adolescents. Although Austrian data provide valuable information on lean and fat mass, they do not cover all relevant BC parameters. Therefore, the objective of this study is twofold: firstly, to establish reference data for body composition parameters in Polish adolescents representative of Central Europe, and secondly, to investigate sex differences in these parameters.

Table 1 presents descriptive data on height, weight, BMI and body composition (BC) parameters for normal-weight male and female adolescents aged 10–18 years.

As expected, boys were generally taller and heavier than girls, with significant differences appearing at age 14 (p < 0.01) and continuing into late adolescence. At age 18, boys were on average 13.8 cm taller and 11.7 kg heavier than girls. The BMI of both boys and girls increased with age, with significant differences emerging at age 13 (p < 0.05), although the difference remained small. At the age of 18, boys had a slightly higher average BMI than girls (21.7 vs. 21.3 kg/m²). Boys had consistently higher values for FFM, BCM, TBW and MM than girls, with significant differences (p < 0.01) starting at age 13 (for FFM), 14 (for BCM, BCMI and MM) or throughout adolescence (for TBW and FFMI). In contrast, girls had higher values of FM, FMI and FM% indicating a higher proportion of body fat (p < 0.01). Notably, FM% decreased with age in boys but increased in girls although, absolute FM increased in both sexes. At the age of 18 years, boys and girls showed significant differences in FFM (57.5 vs. 42.0 kg), BCM (30.6 vs. 21.3 kg), TBW (41.7 vs. 30.7 L) and MM (37.7 vs. 26.5 kg). Specifically, girls had about 1.3 times more FM than boys (15.3 kg vs. 11.8 kg) and about 1.5 times more FM% than boys (27.0% vs. 16.7%).

Throughout adolescence, there was a consistent difference in FMI between boys and girls (p < 0.01). The difference, which was small between 10 and 11 years of age, gradually increased with age. Boys’ FMI remained stable between the ages of 10 and 14 (3.2 kg/m² at age 10 to 2.9 kg/m² at age 14), whereas girls’ FMI increased more significantly, reaching 4.6 kg/m² at age 14. At the age of 18, girls had a 1.6 times higher FMI than boys (5.6 kg/m² vs. 3.7 kg/m²). The increase in FFMI was consistently higher in boys, from 13.9 kg/m² at age 10 to 17.8 kg/m² at age 18, while girls’ FFMI increased from 13.2 kg/m² at age 10 to 15.4 kg/m² at age 18. Body cell mass index (BCMI) also increased in both sexes, with significant differences appearing at age 15 and peaking at 1.7 kg/m² at age 18.

The supplementary files include centile values for BC parameters for boys and girls aged 10 to 18 years, detailed in Tables S1 and S2. Figures 1, 2, and 3 show smoothed centile curves for boys (Fig. 1), girls (Fig. 2) and FFM, BCM and FM indices for both sexes (Fig. 3).

This study presents new age- and sex-specific reference values and charts for various body composition parameters in a large, ethnically homogeneous, normal-weight population of Polish adolescents aged 10–18 years. Moreover, these reference values may serve as benchmarks for other Central European populations. In order to establish healthy ranges and ensure accurate reference points, individuals who were underweight, overweight or obese were excluded from the analysis, as their inclusion could potentially result in skewing the results due to lower lean mass or excess adiposity. Both abnormal weight statuses may bias reference data towards lower/higher extremes and fail to represent the typical healthy adolescent population. Significant discrepancies in FFM and FM were identified between normal-weight and underweight, overweight or obese study participants (data currently undergoing analysis), thereby substantiating the utilisation of a homogeneous, normal-weight cohort to establish baseline references for typical adolescent growth and body composition. This study uniquely includes measures such as BCM, TBW and MM in addition to the more commonly used FFM and FM, thereby improving our understanding of adolescent body composition for screening and clinical purposes.

The results show that body composition measures generally increase with age, reflecting overall growth during adolescence, with boys experiencing a decrease in FM% due to faster lean mass growth during puberty [25]. Boys typically have higher cell mass, muscle mass and water content, while girls have higher FM, FMI and FM%, consistent with differences attributed to genetics, hormones and lifestyle factors during adolescence [26]. During this period, boys experience a surge in testosterone production, which promotes muscle growth and reduces body fat, while girls experience increased levels of oestrogen, which leads to fat accumulation, particularly around the hips and thighs [27].

Although there are generally accepted patterns of growth during adolescence, the timing and intensity of growth spurts can vary significantly between individuals. Some may experience growth spurts earlier or later, with variations in the rate of growth and the timing of sexual maturation stages. Consequently, there is considerable individual variation in body composition parameters, both within and between sexes. It is therefore essential to consider these variations when interpreting findings related to growth during adolescence, as they emphasise the uniqueness of each individual's development during this transitional period.

A comparative analysis of the reference centile values for FFMI and FMI in Polish normal-weight adolescents with data from Austria (LEAD study) [15], the United Kingdom [28], Germany (MoMo study population data) [16] and Tyrol (EVA4YOU study) [29] shows similar overall patterns, with notable differences such as significantly lower 97th (98th in UK) centile values in our dataset, probably due to exclusion of overweight and obese individuals. Raw centile curves for the 3rd (2nd in UK cohort), 50th and 97th (98th in UK cohort) are available in the supplementary material in Figure S1. Raw centile curves for the 3rd, 50th and 97th of our data and the normal-weight subsample of German adolescents (Figure S2 in the supplementary material) demonstrate similar growth trajectories, but with more marked differences for boys. These findings underscore the value of using normal-weight adolescents as a reference benchmark for body composition parameters.

The study addresses the potential impact of diverse measurement techniques on the accuracy of body composition data. The LEAD and UK cohort studies employed DXA, whereas the MoMo and EVA4YOU studies utilised BIA, the same techniques as employed in the present study. BIA is simple, economical and non-invasive method, making it well-suited for population surveys and outpatient clinical applications. Achamrah and colleagues identified only minor discrepancies between these methods when studying over 3000 adult patients, particularly in those with a BMI between 16 and 18 kg/m² [30]. This suggests that the choice of measurement method does not significantly affect comparative results at a population level. However, they found significant discrepancies when assessing individuals, independent of BMI.

The establishment of new reference data for Polish adolescents gives rise to the question of whether local reference data should be prioritised over international benchmarks. The existing literature provides consistent support for the use of local growth references for the monitoring of changes in physical growth during childhood and adolescence [31, 32, 33]. The study conducted by Kułaga and colleagues demonstrates the superiority of local references in capturing population-specific variation in physical growth in Polish children and adolescents compared to international benchmarks [34]. We think that local references are able to account for population-specific variation and provide accurate benchmarks that are tailored to the specific characteristics of the local population. This is particularly important for understanding and monitoring growth patterns and health metrics in specific populations, ensuring that assessments and interventions are appropriately tailored to the distinctive genetic, environmental and cultural factors that influence a local group. Conversely, international references facilitate cross-population analysis and consistency in research, which is essential for clinical practice and global health initiatives. They allow comparisons to be made between different regions and populations, thereby highlighting broader trends and inequalities in health and development. This consistency is essential for multinational studies, global health assessments and the formulation of universal health guidelines. Both types of data are valuable, and the choice depends on the purpose of the study. Local references are ideal for accurate population-specific assessments and interventions, while international references are essential for comparative studies and the establishment of universal health standards.

A key element of body composition assessment is the establishment of cut-off points to facilitate the identification of individuals at risk of various health outcomes. These points serve as critical markers for distinguishing between normal and abnormal body composition. There is no consensus on the optimal cut-off points for these measurements, and recommendations vary between studies. McCarthy and colleagues propose the use of fat mass cut-off points in the second, 85th and 95th centiles to define the underfat, normal, overfat and obese categories, respectively [35]. While there is consensus on the definitions of overweight and obese, it is recommended that the underfat category be defined using the 5th centile rather than the 2nd [36]. It is preferable to establish cut-off points based on the risk of various diseases rather than arbitrary choices based solely on centile thresholds [29, 37]. Given the disparate implications of body composition parameters for health, future research will seek to establish centile values for each parameter, thereby facilitating a more nuanced understanding of healthy and pathological body composition.

The establishment of reference data for body composition in Polish adolescents is of significant scientific importance. These local references account for unique regional physiological and environmental factors, thereby providing a valuable framework for research, screening and clinical assessment. Such data facilitate the early detection and intervention of nutritional deficiencies, promote healthier adolescent development and reduce long-term health risks. Furthermore, these references may serve as a useful reference data for other Central European adolescents.