Implications of leg length for metabolic health and fitness.

Background and objectives: Several studies have linked longer legs with favorable adult metabolic health outcomes and greater offspring birth weight. A recent Mendelian randomization study suggested a causal link between height and cardiometabolic risk; however, the underlying reasons remain poorly understood. Methodology: Using a cross-sectional design, we tested in a convenience sample of 70 healthy young women whether birth weight and tibia length as markers of early-life conditions associated more strongly with metabolically beneficial traits like organ size and skeletal muscle mass (SMM) than a statistically derived height-residual variable indexing later, more canalized growth. Results: Consistent with the 'developmental origins of health and disease' hypothesis, we found relatively strong associations of tibia length-but not birth weight-with adult organ size, brain size, SMM and resting energy expenditure measured by magnetic resonance imaging (MRI), dual-energy X-ray absorptiometry and indirect calorimetry, respectively. Conclusions and implications: Building on prior work, these results suggest that leg length is a sensitive marker of traits directly impacting metabolic and reproductive health. Alongside findings in the same sample relating tibia length and height-residual to MRI-measured pelvic dimensions, we suggest there may exist a degree of coordination in the development of long bone, lean mass and pelvic traits, possibly centered on early, pre-pubertal growth periods. Such phenotypic coordination has important implications for fitness, serving to benefit both adult health and the health of offspring in subsequent generations.

Evaluation of dual-energy X-ray absorptiometry compared to magnetic resonance imaging for collecting measurements of the human bony pelvis.

OBJECTIVES: Imaging methods to measure the human pelvis in vivo provide opportunities to better understand pelvic variation and adaptation. Magnetic resonance imaging (MRI) provides high-resolution images, but is more expensive than dual-energy X-ray absorptiometry (DXA). We sought to compare pelvic breadth measurements collected from the same individuals using both methods, to investigate if there are systematic differences in pelvic measurement between these imaging methods. METHODS: Three pelvic breadth dimensions (bi-iliac breadth, bi-acetabular breadth, medio-lateral inlet breadth) were collected from MRI and DXA scans of a cross-sectional sample of healthy, nulliparous adult women of South Asian ancestry (n = 63). Measurements of MRI and DXA pelvic dimensions were collected four times in total, with one baseline data collection session and three replications. Data collected from these sessions were averaged, used to calculate technical error of measurement and entered into a Bland-Altman analysis. Linear regression models were fitted with a given MRI pelvic measurement regressed on the same measurement collected from DXA scans, as well as MRI mean bias regressed on DXA mean bias. RESULTS: Technical error of measurement was higher in DXA measurements of bi-iliac breadth and medio-lateral pelvic inlet breadth and higher for MRI measurements of bi-acetabular breadth. Bland Altman analyses showed no statistically significant relationship between the mean bias of MRI and DXA, and the differences between MRI and DXA pelvic measurements. CONCLUSIONS: DXA measurements of pelvic breadth are comparable to MRI measurements of pelvic breadth. DXA is a less costly imaging technique than MRI and can be used to collect measurements of skeletal elements in living people.

Sarcopenia and Fat Mass in Children With Chronic Liver Disease and Its Impact on Liver Transplantation.

In adults, weight loss and sarcopenia are prognostic indicators of poor outcomes for patients awaiting liver transplant (LT). We tested the hypothesis that sarcopenia in children awaiting LT was related to poor outcomes. Methods: Children with end-stage chronic liver disease undergoing assessment for LT were recruited into an observational longitudinal study. Anthropometry and body composition (BC; whole-body dual-energy x-ray absorptiometry scan) were assessed before and, on average, 1 year after LT. Results: Eleven children (6 females:5 males) were assessed (4.7 to 17.2 years; median, 9.9) at baseline. Nine children went on to have an LT. The aspartate aminotransferase-to-platelet ratio index had a significant positive correlation with trunk lean mass and trunk lean mass index (LMI) SD score (SDS). At baseline, 4 patients were sarcopenic with appendicular LMI SDS less than -1.96. All fat mass and fat mass index (FMI) SDSs were within the normal range (above -1.96). There was a strong negative correlation between FMI SDS and height SDS. After transplant, there was a significant reduction in trunk LMI from 1.20 to -0.51 (95% CI, 1.03-2.4; P < 0.01). Body mass index SDS had a negative correlation with days to discharge after transplant. The majority of patients discharged after 16 days were sarcopenic. One year after transplantation, all patients were alive with normal graft function regardless of BC before LT. Conclusion: FMIs were normal regardless of LMIs and correlated negatively with height. BC was related to days to discharge after LT but not to outcomes a year after LT.

Body composition data show that high BMI centiles overdiagnose obesity in children aged under 6 years.

BACKGROUND: Most authorities define childhood overweight/obesity as a BMI exceeding the same high centile cutoff at all ages, but it seems unlikely that true obesity prevalence (excess body fat) is constant throughout childhood. OBJECTIVES: We investigated how fat mass (FM) and lean mass (LM), adjusted for height, relate to BMI and each other across childhood, using a uniquely large database of body composition measures, estimated using gold standard methods. METHODS: Cross-sectional and cohort data were collated from representative samples of healthy children aged 6 wk to 20 y and children attending obesity clinics aged 7-16 y. Body composition was measured by deuterium dilution up to age 4 y, and by either deuterium or the criterion 4-component model from 4 to 20 y. FM and LM were expressed, respectively, as fat mass index (FMI; FM/height2) and lean mass index (LMI; LM/height2). RESULTS: There were 2367 measurements of weight, height, and body composition from 1953 individuals. Before age 6 y, the variability in FMI, LMI, and BMI was much less than after; FMI was low (mainly <8 kg/m2) and FMI and LMI were weakly negatively correlated. From mid-childhood, upper limits for both BMI and FMI rose, but FMI in children with BMI <91st centile still rarely exceeded 8. With increasing age, the correlation of FMI with LMI rose to 0.5-0.7, driven mainly by children with a high FMI also having a high LMI. CONCLUSIONS: Raised fat levels are much less common at younger than older ages, and young children with a high BMI centile have lower FMI than older children with the same BMI centile. Current BMI centile cutoffs thus overdiagnose obesity in younger groups. More stringent cutoffs are required for children aged <6 y, matching the WHO recommendation for 0-5 y.

Utility of specific bioelectrical impedance vector analysis for the assessment of body composition in children.

BACKGROUND & AIMS: Bioelectrical impedance analysis (BIA) is widely considered a body composition technique suitable for routine application. However, its utility in sick or malnourished children is complicated by variability in hydration. A BIA variant termed vector analysis (BIVA) aims to resolve this, by differentiating hydration from cell mass. However, the model was only partially supported by children's data. To improve accuracy, further adjustment for body shape variability has been proposed, known as specific BIVA (BIVAspecific). METHODS: We re-analysed body composition data from 281 children and adolescents (46% male) aged 4-20 years of European ancestry. Measurements included anthropometry, conventional BIA, BIVA outcomes adjusted either for height (BIVAconventional), or for height and body cross-sectional area (BIVAspecific), and fat-free mass (FFM) and fat mass (FM) by the criterion 4-component model. Graphic analysis and regression analysis were used to evaluate different BIA models for predicting FFM and FM. RESULTS: Age was strongly correlated with BIVAconventional parameters, but weakly with BIVAspecific parameters. FFM correlated more strongly with BIVAconventional than with BIVAspecific parameters, whereas the opposite pattern was found for FM. In multiple regression analyses, the best prediction models combined conventional BIA with BIVAspecific parameters, explaining 97.0% and 89.8% of the variance in FFM and FM respectively. These models could be further improved by incorporating body weight. CONCLUSIONS: The prediction of body composition can be improved by combining two different theoretical models, each of which appears to provide different information about the two components FFM and FM. Further work should test the utility of this approach in pediatric patients.

Growth, Body Composition, and Lung Function in Prepubertal Children with Cystic Fibrosis Diagnosed by Newborn Screening.

BACKGROUND: Children with cystic fibrosis (CF) are at risk of altered body composition (BC). Newborn screening (NBS) may lead to improved BC outcomes. We investigated BC and its relationship with lung function in prepubertal children diagnosed with CF by NBS. Secondary aims explored predictors of fat-free mass (FFM) and lung function. METHODS: Thirty-seven screened (non-meconium ileus) children with CF (20 boys) born 2007-2012 had a dual-energy x-ray absorptiometry scan at 5-8 years to determine whole-body (WB) and appendicular BC. Anthropometry was performed and routine spirometry recorded. Results were converted to z-scores, height-adjusted (fat mass index [FMI] and FFM index [FFMI]) and compared with population mean values. Predictors of forced expiratory volume in 1 second (FEV1 ) were assessed using linear regression. RESULTS: Height, body mass index (BMI), and FEV1 were within normal limits, however, weight and BC were significantly low compared with reference data (weight, P = .03; WB FMI, P = .001; WB FFMI, P = .009). Gender differences were detected, with lower appendicular BC in boys and lower weight, BMI, and BC in girls. The association between FEV1 and WB FFMI (r = 0.38; P = .02) was stronger than with BMI (r = 0.29; P = .08). WB FFMI was the only significant predictor of FEV1 in a multivariable model (95% CI, 0.11-0.99; P = .016). CONCLUSION: In this NBS CF population, gender differences in growth and BC were apparent despite preserved lung function. These results support BC assessment in prepubertal children, particularly girls, with an opportunity to direct interventions to optimize FFM.

Associations of age and body mass index with hydration and density of fat-free mass from 4 to 22 years.

BACKGROUND: Most body composition techniques assume constant properties of fat free mass (FFM) (hydration and density) regardless of nutritional status, which may lead to biased values. AIM: To evaluate the interactive associations of age and body mass index (BMI) with hydration and density of FFM. METHODS: Data from subjects aged between 4 and 22 years old from several studies conducted in London, UK were assessed. Hydration (HFFM) and density (DFFM) of FFM obtained from the four-component model in 936 and 905 individuals, respectively, were assessed. BMI was converted in to z-scores, and categorised into five groups using z-score cut-offs (thin, normal weight, overweight, obese, and severely obese). Linear regression models for HFFM and DFFM were developed using age, sex, and BMI group as predictors. RESULTS: Nearly 30% of the variability in HFFM was explained by models including age and BMI groups, showing increasing HFFM values in heavier BMI groups. On the other hand, ∼40% of variability in DFFM was explained by age, sex, and BMI groups, with DFFM values decreasing in association with higher BMI group. CONCLUSION: Nutritional status should be considered when assessing body composition using two-component methods, and reference data for HFFM and DFFM is needed for higher BMI groups to avoid bias. Further research is needed to explain intra-individual variability in FFM properties.

Development and validation of a prediction model for fat mass in children and adolescents: meta-analysis using individual participant data.

OBJECTIVES: To develop and validate a prediction model for fat mass in children aged 4-15 years using routinely available risk factors of height, weight, and demographic information without the need for more complex forms of assessment. DESIGN: Individual participant data meta-analysis. SETTING: Four population based cross sectional studies and a fifth study for external validation, United Kingdom. PARTICIPANTS: A pooled derivation dataset (four studies) of 2375 children and an external validation dataset of 176 children with complete data on anthropometric measurements and deuterium dilution assessments of fat mass. MAIN OUTCOME MEASURE: Multivariable linear regression analysis, using backwards selection for inclusion of predictor variables and allowing non-linear relations, was used to develop a prediction model for fat-free mass (and subsequently fat mass by subtracting resulting estimates from weight) based on the four studies. Internal validation and then internal-external cross validation were used to examine overfitting and generalisability of the model's predictive performance within the four development studies; external validation followed using the fifth dataset. RESULTS: Model derivation was based on a multi-ethnic population of 2375 children (47.8% boys, n=1136) aged 4-15 years. The final model containing predictor variables of height, weight, age, sex, and ethnicity had extremely high predictive ability (optimism adjusted R2: 94.8%, 95% confidence interval 94.4% to 95.2%) with excellent calibration of observed and predicted values. The internal validation showed minimal overfitting and good model generalisability, with excellent calibration and predictive performance. External validation in 176 children aged 11-12 years showed promising generalisability of the model (R2: 90.0%, 95% confidence interval 87.2% to 92.8%) with good calibration of observed and predicted fat mass (slope: 1.02, 95% confidence interval 0.97 to 1.07). The mean difference between observed and predicted fat mass was -1.29 kg (95% confidence interval -1.62 to -0.96 kg). CONCLUSION: The developed model accurately predicted levels of fat mass in children aged 4-15 years. The prediction model is based on simple anthropometric measures without the need for more complex forms of assessment and could improve the accuracy of assessments for body fatness in children (compared with those provided by body mass index) for effective surveillance, prevention, and management of clinical and public health obesity.

Resting Energy Expenditure of Children With End-stage Chronic Liver Disease Before and After Liver Transplantation.

OBJECTIVES: Our objective was to test the hypothesis that children with end-stage chronic liver disease (ESCLD) are hypermetabolic when compared to healthy children, and that this hypermetabolism persists for at least 6 months after liver transplant. METHODS: Seventeen patients with end-stage chronic liver disease and 14 healthy controls had their resting energy expenditure measured (mREE) by indirect calorimetry. Weight, height, and body mass index were converted to standard deviation (SD) scores. Children older than 5 years had air displacement plethysmography and patients older than 5 years also had whole body dual-energy X-ray absorptiometry with characterization of fat mass (FM), fat-free mass (FFM), and bone-free fat free (lean) mass. RESULTS: When compared to the prediction equation 44% of the patients and 50% of the healthy controls were hypermetabolic. The younger patients (0-5 years) had a lower mREE than the healthy controls but were significantly lighter and shorter than their healthy counterparts. mREE correlated strongly for all children with age, weight, height, and FFM. There was a strong negative correlation between age and mREE/kg in both patients (rs = -0.94, P < 0.01) and controls (rs = -0.91, P < 0.01). Almost 84% of the variance in mREE was explained by age (P < 0.001). There were no significant differences between resting energy expenditure (REE)/FFM between the 2 groups. mREE/kg before liver transplant correlated with mREE/kg after transplant (Pearson r = 0.83, P < 0.01). CONCLUSIONS: REE mostly reflected the size of the child. The patients were not hypermetabolic when compared to the healthy children. The main determinant of REE/kg after transplant was REE/kg before transplant.

Bio-electrical impedance vector analysis: testing Piccoli's model against objective body composition data in children and adolescents.

BACKGROUND/OBJECTIVES: Bio-electrical impedance (BI) analysis is a simple body composition method ideal for children. However, its utility in sick or malnourished children is complicated by variability in hydration. BI vector analysis (BIVA) potentially resolves this, using a theoretical model that differentiates hydration from cell mass. We tested this model against reference methods in healthy children varying widely in age and nutritional status. SUBJECTS/METHODS: We compiled body composition data from 291 children and adolescents (50% male) aged 4-20 years of European ancestry. Measurements included anthropometry, BIVA outcomes (height-adjusted resistance (R/H) and reactance (Xc/H); phase angle (PA)), and fat-free mass (FFM), fat mass (FM) and FFM-hydration (HFFM) by the criterion 4-component model. All outcomes were converted to age- and sex-standardised standard deviation scores (SDS). Graphic analysis and regression analysis were used to evaluate the BIVA model. RESULTS: R/H and Xc/H declined with age in curvilinear manner, whereas PA increased linearly with age. R/H-SDS and Xc-SDS were negatively correlated with FFM-SDS, HFFM-SDS. and FM-SDS. PA was positively correlated with FFM-SDS but unrelated to HFFM-SDS and FM-SDS. CONCLUSIONS: While previous studies of adults with major fluid perturbations support the BIVA model, it is less successful in predicting variability in FFM in healthy children and adolescents. BIVA outcomes varied as predicted by the model with HFFM, but not as predicted with FFM. Variability in adiposity also explains some of the variability in BIVA traits. Further work is needed to develop a theoretical BIVA model for application in paediatric patients without major fluid disturbances.

Metabolic rate of major organs and tissues in young adult South Asian women.

BACKGROUND/OBJECTIVES: Major organ-specific and tissue-specific metabolic rate (Ki) values were initially estimated using in vivo methods, and values reported by Elia (Energy metabolism: tissue determinants and cellular corollaries, Raven Press, New York, 1992) were subsequently supported by statistical analysis. However, the majority of work to date on this topic has addressed individuals of European descent, whereas population variability in resting energy metabolism has been reported. We aimed to estimate Ki values in South Asian females. SUBJECTS/METHODS: This cross-sectional study recruited 70 healthy young women of South Asian ancestry. Brain and organs were measured using magnetic resonance imaging, skeletal muscle mass by dual-energy X-ray absorptiometry, fat mass by the 4-component model, and whole-body resting energy expenditure by indirect calorimetry. Organ and tissue Ki values were estimated indirectly using regression analysis through the origin. Preliminary analysis suggested overestimation of heart mass, hence the modeling was repeated with a literature-based 22.5% heart mass reduction. RESULTS: The pattern of derived Ki values across organs and tissues matched that previously estimated in vivo, but the values were systematically lower. However, adjusting for the overestimation of heart mass markedly improved the agreement. CONCLUSIONS: Our results support variability in Ki values among organs and tissues, where some are more metabolically "expensive" than others. Initial findings suggesting lower organ/tissue Ki values in South Asian women were likely influenced by heart mass estimation bias. The question of potential ethnic variability in organ-specific and tissue-specific energy metabolism requires further investigation.

Maternal investment, life-history strategy of the offspring and adult chronic disease risk in South Asian women in the UK.

BACKGROUND AND OBJECTIVES: Patterns of development predict cardiovascular disease (CVD) risk, and ethnic differences therein, but it remains unclear why apparently 'adaptive plasticity' in early life should generate health costs in later life. We hypothesized that offspring receiving low maternal investment during fetal life, the primary period of organogenesis, should predict a shorter reproductive career and develop a fast life-history strategy, prioritizing reproduction over growth and homeostatic maintenance. METHODOLOGY: We studied 58 young adult South Asian women living in the UK, a group with high susceptibility to CVD. We obtained gestational age, birth weight (BW) and menarcheal age by recall and measured anthropometry, body composition, resting metabolic rate (RMR) and blood pressure (BP). RESULTS: BW and gestational age were inversely associated with menarcheal age, indicating that lower maternal investment is associated with faster maturation. Menarcheal age was positively associated with height but inversely with adiposity, indicating that rapid maturation prioritizes lipid stores over somatic growth. BW was inversely associated with BP, whereas adiposity was positively associated, indicating that lower maternal investment reduces BP homeostasis. BW was positively associated with RMR, whereas menarche was inversely associated, indicating that maternal investment influences adult metabolism. CONCLUSIONS AND IMPLICATIONS: Supporting our hypothesis, low maternal investment promoted faster life histories, demonstrated by earlier menarche, reduced growth and elevated adiposity. These traits were associated with poorer BP regulation. This is the first study demonstrating strategic adjustment of the balance between reproduction and metabolic health in response to the level of maternal investment during fetal life.

Use of fat mass and fat free mass standard deviation scores obtained using simple measurement methods in healthy children and patients: comparison with the reference 4-component model.

BACKGROUND: Clinical application of body composition (BC) measurements for individual children has been limited by lack of appropriate reference data. OBJECTIVES: (1) To compare fat mass (FM) and fat free mass (FFM) standard deviation scores (SDS) generated using new body composition reference data and obtained using simple measurement methods in healthy children and patients with those obtained using the reference 4-component (4-C) model; (2) To determine the extent to which scores from simple methods agree with those from the 4-C model in identification of abnormal body composition. DESIGN: FM SDS were calculated for 4-C model, dual-energy X-ray absorptiometry (DXA; GE Lunar Prodigy), BMI and skinfold thicknesses (SFT); and FFM SDS for 4CM, DXA and bioelectrical impedance analysis (BIA; height(2)/Z)) in 927 subjects aged 3.8-22.0 y (211 healthy, 716 patients). RESULTS: DXA was the most accurate method for both FM and FFM SDS in healthy subjects and patients (mean bias (limits of agreement) FM SDS 0.03 (± 0.62); FFM SDS -0.04 (± 0.72)), and provided best agreement with the 4-C model in identifying abnormal BC (SDS ≤-2 or ≥ 2). BMI and SFTs were reasonable predictors of abnormal FM SDS, but poor in providing an absolute value. BIA was comparable to DXA for FFM SDS and in identifying abnormal subjects. CONCLUSIONS: DXA may be used both for research and clinically to determine FM and FFM SDS. BIA may be used to assess FFM SDS in place of DXA. BMI and SFTs can be used to measure adiposity for groups but not individuals. The performance of simpler techniques in monitoring longitudinal BC changes requires investigation. Ultimately, the most appropriate method should be determined by its predictive value for clinical outcome.

Body composition in young children with cystic fibrosis.

Malnutrition in cystic fibrosis is an indication of poor prognosis and measurement of body composition may aid in identifying those at risk of poor clinical outcome. There is growing evidence of patients with cystic fibrosis having high fat and/or low fat-free mass which is likely to affect prognosis. Simple body composition techniques are based on assumptions about the nature of the fat-free mass and may therefore be biased; however, these techniques may be helpful in identifying children with high fat or low fat-free mass. The 'gold standard' 4-component model of body composition allows for more accurate assessment of fat mass and the components of fat-free mass.

Activity, body composition and bone health in children.

OBJECTIVE: To examine relationships among daily activity levels, body composition and bone outcomes in children aged 6.7 years who were born at term with birth weights <20th centile. METHODS: Activity data collected using accelerometers were correlated with body composition and bone outcome z-scores from dual-energy X-ray absorptiometry in 36 children. RESULTS: Activity levels were related to body composition outcomes; for example, lean mass index (lean mass/height(2)) was positively associated with time spent in moderate activity (r=0.40, p=0.02) and negatively with time spent in sedentary activity (r=-0.50, p=0.002). Per cent time spent in sedentary activity correlated negatively with whole body bone mineral density z-score (r=-0.44, p=0.01) and hip bone mineral content (r=-0.38, p=0.03). CONCLUSIONS: Moderate and vigorous activity levels were associated with increased lean and bone mass in this population but not with conventional measures of adiposity such as weight and body mass index z-scores. Standard measures of adiposity may mask potential benefits of regular activity.

Body-composition reference data for simple and reference techniques and a 4-component model: a new UK reference child.

BACKGROUND: A routine pediatric clinical assessment of body composition is increasingly recommended but has long been hampered by the following 2 factors: a lack of appropriate techniques and a lack of reference data with which to interpret individual measurements. Several techniques have become available, but reference data are needed. OBJECTIVE: We aimed to provide body-composition reference data for use in clinical practice and research. DESIGN: Body composition was measured by using a gold standard 4-component model, along with various widely used reference and bedside methods, in a large, representative sample of British children aged from 4 to ≥20 y. Measurements were made of anthropometric variables (weight, height, 4 skinfold thicknesses, and waist girth), dual-energy X-ray absorptiometry, body density, bioelectrical impedance, and total body water, and 4-component fat and fat-free masses were calculated. Reference charts and SD scores (SDSs) were constructed for each outcome by using the lambda-mu-sigma method. The same outcomes were generated for the fat-free mass index and fat mass index. RESULTS: Body-composition growth charts and SDSs for 5-20 y were based on a final sample of 533 individuals. Correlations between SDSs by using different techniques were ≥0.68 for adiposity outcomes and ≥0.80 for fat-free mass outcomes. CONCLUSIONS: These comprehensive reference data for pediatric body composition can be used across a variety of techniques. Together with advances in measurement technologies, the data should greatly enhance the ability of clinicians to assess and monitor body composition in routine clinical practice and should facilitate the use of body-composition measurements in research studies.

Body composition assessed by the 4-component model and association with lung function in 6-12-y-old children with cystic fibrosis.

BACKGROUND: Malnutrition is an indicator of a poor prognosis in patients with cystic fibrosis (CF). Previous body-composition (BC) studies in children with CF used 2-component models (2CMs) to assess fat mass (FM) and fat-free mass (FFM), but to our knowledge no study has used the gold-standard 4-component model (4CM), which allows for a more accurate evaluation of the nature of both elements. OBJECTIVE: We measured BC by using the 4CM in 6-12-y-old children with CF to 1) compare findings with those of healthy, matched control children and reference data; 2) relate BC to lung spirometry [forced expired volume in 1 s (FEV1)]; and 3) compare findings with those from more commonly used 2CM techniques. DESIGN: One hundred clinically stable children with CF (57% girls) aged 6-12 y were measured by using the 4CM. Children with CF underwent spirometry (FEV1). RESULTS: Girls with CF had significantly less FM than did healthy girls, even after adjustment for height and pubertal status; boys with CF had higher body mass index SD scores than did healthy boys. FM in girls was positively associated with the FEV1 percentage predicted. The 2CM FM was significantly different from the 4CM FM, with differences dependent on sex and condition, although most techniques identified a relation between FM and FEV1 in girls. CONCLUSIONS: Although shorter than healthy children, boys with CF were heavier and had a BC within the normal range; however, girls with CF had lower FM than did healthy girls, and this was associated with poorer lung function. Given the worse prognosis in girls, this finding merits more attention. The reliability of 2CM techniques varied with sex and health status.

Pediatric reference data for lean tissue properties: density and hydration from age 5 to 20 y.

BACKGROUND: Hydrometry and densitometry are widely used to assess pediatric body composition due to their ease of application. The accuracy of these techniques depends on the validity of age- and sex-specific constant values for lean tissue hydration or density. Empirical data on these constants, and their variability between individuals, are lacking. OBJECTIVES: The objectives were to measure lean tissue hydration and density in a large sample of children and adolescents and to derive prediction equations. DESIGN: Body composition was measured in 533 healthy individuals (91% white) aged 4-23 y by using the 4-component model. Age- and sex-specific median values for hydration and density were obtained by using the LMS (lambda, mu, sigma) method. Regression analysis was used to generate prediction equations on the basis of age, sex, and body mass index SD score (BMI SDS). Values were compared with those in previously published predictions. RESULTS: Age-associated changes in density and hydration differed between the sexes. Compared with our empirical values, use of published values resulted in a mean bias of 2.1% fat (P < 0.0001). Age, sex, and BMI SDS were all significant predictors of lean tissue hydration and density. With adjustment for age and sex, hydration was higher, and density lower, in higher-BMI SDS individuals. CONCLUSIONS: The chemical maturation of lean tissue is not a linear process and proceeds differently in males and females. Previously published reference values are inaccurate and induce clinically significant bias in percentage fat. New empirical reference values are provided for use in pediatric hydrometry and densitometry. Further research that extends to cover nonwhite ethnic groups is needed.

Validation of BIA in obese children and adolescents and re-evaluation in a longitudinal study.

Decrease in fat mass (FM) is a one of the aims of pediatric obesity treatment; however, measurement techniques suitable for routine clinical assessment are lacking. The objective of this study was to validate whole-body bioelectrical impedance analysis (BIA; TANITA BC-418MA) against the three-component (3C) model of body composition in obese children and adolescents, and to test the accuracy of our new equations in an independent sample studied longitudinally. A total of 77 white obese subjects (30 males) aged 5-22 years, BMI-standard deviation score (SDS) 1.6-3.9, had measurements of weight, height (HT), body volume, total body water (TBW), and impedance (Z). FM and fat-free mass (FFM) were calculated using the 3C model or predicted from TANITA. FFM was predicted from HT(2)/Z. This equation was then evaluated in 17 other obese children (5 males) aged 9-13 years. Compared to the 3C model, TANITA manufacturer's equations overestimated FFM by 2.7 kg (P < 0.001). We derived a new equation: FFM = -2.211 + 1.115 (HT(2)/Z), with r(2) of 0.96, standard error of the estimate 2.3 kg. Use of this equation in the independent sample showed no significant bias in FM or FFM (mean bias 0.5 +/- 2.4 kg; P = 0.4), and no significant bias in change in FM or FFM (mean bias 0.2 +/- 1.8 kg; P = 0.7), accounting for 58% (P < 0.001) and 55% (P = 0.001) of the change in FM and FFM, respectively. Our derived BIA equation, shown to be reliable for longitudinal assessment in white obese children, will aid routine clinical monitoring of body composition in this population.

Early diet and peak bone mass: 20 year follow-up of a randomized trial of early diet in infants born preterm.

BACKGROUND: Preterm infants are at risk of metabolic bone disease due to inadequate mineral intake with unknown consequences for later bone health. OBJECTIVE: To test the hypotheses that (1) early diet programs peak bone mass and bone turnover; (2) human milk has a beneficial effect on these outcomes; (3) preterm subjects have reduced peak bone mass compared to population reference data. DESIGN: 20 year follow-up of 202 subjects (43% male; 24% of survivors) who were born preterm and randomized to: (i) preterm formula versus banked breast milk or (ii) preterm versus term formula; as sole diet or supplement to maternal milk. Outcome measures were (i) anthropometry; (ii) hip, lumbar spine (LS) and whole body (WB) bone mineral content (BMC) and bone area (BA) measured using DXA; (iii) bone turnover markers. RESULTS: Infant dietary randomization group did not influence peak bone mass or turnover. The proportion of human milk in the diet was significantly positively associated with WBBA and BMC. Subjects receiving >90% human milk had significantly higher WBBA (by 3.5%, p=0.01) and BMC (by 4.8%, p=0.03) than those receiving <10%. Compared to population data, subjects had significantly lower height SDS (-0.41 (SD 1.05)), higher BMI SDS (0.31 (1.33)) and lower LSBMD SDS (-0.29 (1.16)); height and bone mass deficits were greatest in those born SGA with birthweight <1250 g (height SDS -0.81 (0.95), LSBMD SDS -0.61 (1.3)). CONCLUSION: Infant dietary randomization group did not affect peak bone mass or turnover suggesting the observed reduced final height and LS bone mass, most marked in growth restricted subjects with the lowest birthweight, may not be related to sub-optimal early nutrition. The higher WB bone mass associated with human milk intake, despite its low nutrient content, may reflect non-nutritive factors in breast milk. These findings may have implications for later osteoporosis risk and require further investigation.