Relationship between Birth Weight, Early Growth Rate, and Body Composition in 5- to 7-Year-Old Children

BACKGROUND

Programing of body composition during intrauterine growth may contribute to the higher risk for cardio-metabolic disease in individuals born small or large for gestational age (SGA, LGA). Compensations of intrauterine growth by catch-up or catch-down postnatal growth may lead to adverse consequences like a thin-fat phenotype.

METHODS

The impact of (i) birth weight as well as (ii) the interaction between birth weight and catch-up or catch-down growth during the first 2 years of life on fat-free mass index (FFMI) and fat mass index (FMI) in 3,204 5-7-year-old children were investigated using Hattori's body composition chart. Body composition results were compared to appropriate for gestational age (AGA) birth weight with the same body mass index (BMI).

RESULTS

In total, 299 children at age 5-7 years were categorized as SGA, 2,583 as AGA, and 322 as LGA. When compared to AGA-children, BMI at 5-7 years of age was higher in LGA-children (15.5 vs. 16.2 kg/m2; p < 0.001) but not different in SGA-children. Compared to AGA with the same BMI, LGA was associated with higher FMI and a lower FFMI in 5-7-year-old girls. This phenotype was also seen for both sexes with catch-down growth during the first 2 years of life whereas catch-up growth prevented the higher FMI and lower FFMI per BMI. By contrast, SGA was associated with a higher FFMI and lower FMI in 5-7-year-old boys compared to AGA boys with the same BMI. This phenotype was also seen with catch-down growth in both genders whereas catch-up growth in girls led to more gain in FMI per BMI.

CONCLUSION

LGA with a compensatory catch-down postnatal growth may be a risk factor for the development of disproportionate gain in fat over lean mass whereas SGA with a catch-down postnatal growth seems to favor the subsequent accretion of lean over fat mass. A higher propensity of lean mass accretion during postnatal growth in boys compared to girls explains sex differences in these phenotypes.

Body Composition Characteristics of a Load-Capacity Model: Age-Dependent and Sex-Specific Percentiles in 5- to 17-Year-Old Children

INTRODUCTION

Body composition assessment is superior to the use of body mass index (BMI) to characterize the nutritional status in pediatric populations. For data interpretation, suitable reference data are needed; hence, we aimed to generate age-dependent and sex-specific body composition reference data in a larger population of children and adolescents in Germany.

METHODS

This is a cross-sectional study on a representative group of 15,392 5- to 17-year-old children and adolescents. Body composition was assessed by bioelectrical impedance analysis using a population-specific algorithm validated against air displacement plethysmography. Age- and sex-specific percentiles for BMI, fat mass index (FMI), fat-free mass index (FFMI), and a "load-capacity model" (characterized by the ratios of fat mass [FM]/ fatt-free mass [FFM] and FM/FFM2) were modeled using the LMS method.

RESULTS

BMI, FMI, FFMI, FM/FFM, and FM/FFM2 curves showed similar shapes between boys and girls with steady increases in BMI, FMI, and FFMI, while FM/FFM2-centiles decreased during early childhood and adolescence. Sex differences were observed in FMI and FM/FFM percentiles with increases in FMI up to age 9 years followed by a steady decrease in FM/FFM during and after puberty with a fast-growing FFMI up to age 17 in boys. The prevalence of low FFM relative to FM reached more than 60% in overweight children and adolescents.

CONCLUSION

These pediatric body composition reference data enable physicians and public health scientists to monitor body composition during growth and development and to interpret individual data. The data point out to an early risk of sarcopenia in overweight children and adolescents.

Family and Lifestyle Factors Mediate the Relationship between Socioeconomic Status and Fat Mass in Children and Adolescents

Socioeconomic status (SES) is strongly associated with childhood overweight. The underlying mechanism and the role of family and lifestyle factors as potential mediators of this relationship remain, however, unclear. Cross-sectional data of 4,772 girls and boys aged 5-16 years from the Kiel Obesity Prevention Study were considered in mediation analyses. Fat mass (FM) was assessed by bioelectrical impedance analysis and converted into a percent FM SD score (FM%-SDS). SES was defined by the parental educational level, classified as low, middle, or high. Characteristics of family and lifestyle factors were obtained via validated questionnaires and considered as mediators. In 3 different age groups, the product-of-coefficients method was used to examine age-specific mediator effects on the relationship between SES and FM%-SDS (c = total effects) and their ratio to total effects, adjusted for age, sex, puberty, and nationality. The prevalence of overweight was 6.9%. In all age groups, SES was inversely associated with FM%-SDS as follows: 5-7 years, c1 = -0.11 (95% CI -0.19 to -0.03); 9-11 years, c2 = -0.21 (95% CI -0.27 to -0.14); and 13-16 years, c3 = -0.23 (95% CI -0.28 to -0.17). The relationship between SES and FM%-SDS was fully (5-7 and 9-11 years) and partly (13-16 years) mediated by similar and age-specific mediators, including parental BMI, parental smoking habits, media consumption, physical activity, and shared meals. Overall, these variables resulted in a total mediating effect of 77.8% (5-7 years), 82.4% (9-11 years), and 70.6% (13-16 years). Consistent for both sexes, the relationship between SES and FM%-SDS was therefore mediated by parental weight status, risk-related behavior within families, and children's and adolescents' lifestyle factors. Strategies for obesity prevention, which are predominantly targeted at socially disadvantaged groups, should therefore address the family environment and lifestyle factors.