Fat-free Mass In Children Research Articles

Air Displacement Plethysmography is an Accurate and Feasible Noninvasive Measure of Fat-Free Mass in Children With Intestinal Failure.

The nutritional status of children with intestinal failure (IF) can be difficult to determine using body weight and currently available anthropometric techniques. Air displacement plethysmography (ADP) is a noninvasive measure of whole-body composition that measures body mass and volume, with a calculation of percent body fat (%BF) and fat-free mass (FFM) that may be useful during the provision of specialized nutrition. To evaluate the validity and feasibility of measuring body composition in children with IF using ADP compared with deuterium dilution (DD), as well as secondarily with other measures of body composition, namely bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry (DXA), and four-site skinfold anthropometry. We conducted a prospective cohort study of 18 children recruited through the Center for Advanced Intestinal Rehabilitation at Boston Children's Hospital. Patients 2-17 years of age with IF dependent on parenteral nutrition (PN) for more than 90 days were included. Spearman rank correlation and Bland-Altman limits of agreement (LOA) analysis were used to compare ADP to 4 alternative measures of body composition. Eighteen children with IF, median age 7.1 [interquartile range (IQR) 5.4-9.3] years, 9 female (50%), and median residual bowel length 31 (IQR 22-85) cm were enrolled. Median PN energy intake was 46 (IQR 39-49) kcal/kg/day. Incomplete bladder emptying lead to invalid measures of DD in 4 subjects. Spearman correlation coefficients for %BF were low to moderate between ADP and DD ( r = 0.29), DXA ( r = 0.62), BIA ( r = 0.50), and skinfold ( r = 0.40). Correlations for FFM were high between ADP and these other measures (range 0.95-0.98). Comparing ADP with DD and skinfold measures, Bland-Altman analysis showed small mean bias (-1.9 and +1.5 kg) and acceptable 95% LOA ranges (10.7 and 22.9 kg), respectively, with larger bias (-10.7 and -7.7 kg) and LOA ranges (38.7 and 45.2 kg) compared to DXA and BIA. %BF by ADP and skinfold thickness were moderately correlated ( r = 0.43) with low bias (-0.2%) but very wide LOA (25.7%). Body composition via ADP is feasible and valid in children with IF as a measure of FFM but appears less suitable for the measurement of %BF. The technique holds promise as a noninvasive measure of body composition to assess the efficacy of nutritional, medical, and surgical interventions.

Maternal Weight Gain during Pregnancy and the Developing Autonomic Nervous System—Possible Impact of GDM

The intrauterine environment is known to affect the offspring's long-term risk for obesity and diabetes. Previous data show that maternal metabolism and gestational weight gain (GWG) are associated with fetal autonomic nervous system (ANS) function, which can be assessed with heart rate variability (HRV). We investigated whether this association is also present in 2-year-old children and addressed the impact of gestational diabetes (GDM). We examined the 2-year-old offspring of mothers who had undergone a 5-point, 75 g oral glucose tolerance test during pregnancy. To assess HRV, a 10-minute ECG was recorded, and time domain and frequency domain parameters were analyzed. Body composition was assessed using bioelectrical impedance testing. We examined 67 children (33 girls, 34 boys), 30 of whom were born to mothers with treated GDM and normoglycemic pregnancies (NGT), respectively. No differences were found between the groups with regard to birth weight, weight at the age of 2 years, and body fat content. We observed that GWG was associated with heart rate and HRV, indicating that children of mothers with low GWG had a lower parasympathetic tone. This association was detected in NGT-exposed-but not in GDM-exposed-children. HR and HRV correlated with body fat and fat-free mass in children from normoglycemic pregnancies only. We found that the impact of maternal GWG on offspring ANS function was missing in the presence of treated GDM. The balance of the ANS was related to offspring body composition in children from NGT pregnancies only. Our results suggest that maternal weight gain during pregnancy has a critical impact on the developing ANS, which might be disturbed in the presence of GDM.

Is an Exercise Intervention the only way to Reduce Visceral Fat without Reducing Fat-free Mass in Children and Adolescents?

Objectives: To maintain proper development, it is recommended that children/adolescents focus more on increasing physical activity than dietary restriction when treating obesity. In other words, adults are better able to tolerate the reductions in fat-free body mass that often occur when trying to lose fat mass. In contrast, children and adolescents should avoid losses in fat-free mass in order to ensure proper development. Therefore, when trying to reduce visceral fat in children via a negative energy balance (i.e., exercise with or without calorie restriction), it is necessary to set desirable conditions in order to minimize the loss of fat-free mass. To determine whether this is possible, we reviewed literature discussing the relationship between changes in visceral fat obtained by abdominal imaging and changes in total body fat and fat-free mass after exercise training with and without calorie restriction in children and adolescents.Methods: Literature review.Results and Conclusions: Previous work found no reduction in fat-free mass in the exercise interventions in which there was no dietary-induced calorie restriction. This supports the idea that reducing visceral fat by increasing physical activity is the preferred strategy over dietary restriction in children and adolescents. Although factors such as the type (e.g. aerobic and/or resistance) of exercise and the amount (i.e. energy expenditure) of exercise will likely have an effect on the magnitude of change in intra-abdominal visceral fat, the quantity of each that is needed without reducing fat-free mass is currently unknown.

Minimum sample size for external validation of a clinical prediction model with a continuous outcome.

Clinical prediction models provide individualized outcome predictions to inform patient counseling and clinical decision making. External validation is the process of examining a prediction model's performance in data independent to that used for model development. Current external validation studies often suffer from small sample sizes, and subsequently imprecise estimates of a model's predictive performance. To address this, we propose how to determine the minimum sample size needed for external validation of a clinical prediction model with a continuous outcome. Four criteria are proposed, that target precise estimates of (i) R2 (the proportion of variance explained), (ii) calibration-in-the-large (agreement between predicted and observed outcome values on average), (iii) calibration slope (agreement between predicted and observed values across the range of predicted values), and (iv) the variance of observed outcome values. Closed-form sample size solutions are derived for each criterion, which require the user to specify anticipated values of the model's performance (in particular R2 ) and the outcome variance in the external validation dataset. A sensible starting point is to base values on those for the model development study, as obtained from the publication or study authors. The largest sample size required to meet all four criteria is the recommended minimum sample size needed in the external validation dataset. The calculations can also be applied to estimate expected precision when an existing dataset with a fixed sample size is available, to help gauge if it is adequate. We illustrate the proposed methods on a case-study predicting fat-free mass in children.

Strength And Power As Indicators Of Differences In Fiber Type Contributions In Children And Adolescents

PURPOSE: Examine individual patterns of peak torque (PT) and mean power (MP) across a range of angular velocities in children and adolescents and how these patterns relate to measurements of growth. METHODS: Seventeen children (age = 11 ± 0.4 years) and 22 adolescents (age = 14 ± 0.6 years) performed maximal voluntary isometric contractions, isokinetic leg extensions at 60, 120, 180, 240, and 300°·s-1, and 50 consecutive maximal isokinetic leg extensions at 180°·s-1. Patterns of responses for PT and MP across angular velocity were fit with quadratic equations for each subject with r2 values ranging from 0.803-0.934 for PT and 0.908-0.996 for MP, respectively. Derivatives of each quadratic formula quantified velocity-related changes in PT and MP. Each quadratic formula predicted the peak velocity at which torque could be generated (VPT) or the velocity at which the greatest MP would occur (VMP). The percent of fast-twitch fibers (FT%) was estimated from the fatigue index of the 50-repetition test. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and quadriceps femoris muscle cross-sectional area. RESULTS: All measurements of growth, PT, and MP were greater for adolescents than children (p ≤ 0.003). As expected, PT decreased quadratically (p < 0.001), while MP increased quadratically to 180-240°·s-1 (p < 0.001) and plateaued (p = 0.056) or decreased (p < 0.001) to 300°·s-1. VPT was 352 ± 18 Nm for children and 527 ± 34 Nm for adolescents (p < 0.001), while VMP was 216 ± 11 W for children and 268 ± 11 W for adolescents (p < 0.001). FT% was 39 ± 4% for children and 46 ± 4% for adolescents (p < 0.001). Derivatives indicated that PT decreased while MP increased across velocity more rapidly in adolescents than children (p ≤ 0.016). Derivatives of PT vs. velocity exhibited a high relationship with body mass for adolescents (r = -0.727), while derivatives of MP vs. velocity exhibited high relationships with body mass and fat-free mass in children (r = 0.714-0.795). VTQ and VMP exhibited high relationships with age for adolescents (r = 0.884). CONCLUSION: Isometric and isokinetic muscle actions in children and adolescents indirectly demonstrate between growth-related increases in fast-twitch fiber contributions to maximal, voluntary muscle strength and power across the velocity spectrum.

Protein intake during pregnancy and offspring body composition at 6\xa0years: the Generation R Study

PurposeIntra-uterine exposure to protein may affect body composition and may increase the prevalence of childhood adiposity. Therefore, we examined whether protein intake during pregnancy is associated with offspring body composition at the age of 6 years and whether associations differ for animal protein and vegetable protein.MethodsWe included 2694 Dutch mother–child pairs participating in a prospective population-based cohort in Rotterdam, the Netherlands. Energy-adjusted protein was measured in pregnancy using a food-frequency questionnaire and analyzed in quartiles. At a mean age of 6.1 ± 0.4 years, we measured children’s body mass index, and fat-free mass index and fat mass index using dual-energy X-ray absorptiometry. Outcomes were standardized for age and sex. BMI was used to classify children’s overweight status.ResultsAfter adjustment for sociodemographic and lifestyle factors, a higher maternal protein intake was associated with a higher children’s fat-free mass index [difference 0.14 standard deviation (95 % CI 0.03, 0.25) for highest vs. lowest quartile of protein intake], but not with children’s fat mass index or body mass index. Comparable associations were found for animal protein and vegetable protein. Maternal protein intake was not associated with children’s overweight.Conclusions and relevanceThis study suggests that higher protein intake during pregnancy is associated with a higher fat-free mass in children at the age of 6 years, but not with their fat mass. Our results do not suggest specific recommendations regarding maternal protein intake during pregnancy to prevent overweight in the offspring.

Prediction of Fat-Free Mass in Children.

Fat-free mass (FFM) is an important covariate for predicting drug clearance. Models for predicting FFM have been developed in adults but there is currently a paucity of mechanism-based models developed to predict FFM in children. The aim of this study was to develop and evaluate a model to predict FFM in children. A large dataset (496 females and 515 males) was available for model building. Subjects had a relatively wide range of age (3-29years) and body mass index values (12-44.9kg/m(2)). Two types of models (M1 and M2) were developed to describe FFM in children. M1 was fully empirical and based on a linear model that contained all statistically significant covariates and their interactions. M2 was a simpler model that incorporated a maturation process. M1 was developed to provide the best possible description of the data (i.e. a positive control). In addition, a published adult model (M3) was applied directly as a reference description of the data. The predictive performances of the three models were assessed by visual predictive checks and by using mean error (ME) and root mean squared error (RMSE). A test dataset (90 females and 86 males) was available for external evaluation. M1 consisted of nine terms with up to second-level interactions. M2 was a sigmoid hyperbolic model based on postnatal age with an asymptote at the adult prediction (M3). For the index dataset, the ME and 95% CI for M1, M2 and M3 were 0.09 (0.03-0.16), 0.24 (0.14-0.33) and 0.29 (0.06-0.51)kg, respectively, and RMSEs were 1.12 (1.03-1.23), 1.58 (1.46-1.72) and 3.76 (3.54-3.97)kg. A maturation model that asymptoted to an established adult model was developed for prediction of FFM in children. This model was found to perform well in both male and female children; however, the adult model performed similarly to the maturation model for females. The ability to predict FFM in children from simple demographic measurements is expected to improve understanding of human body structure and function with direct application to pharmacokinetics.

Increased resting energy expenditure by fat-free mass in children and teenagers with constitutional leanness

To compare the resting energy expenditure (REE) and the REE/Fat-free-mass (FFM) quotient in children with constitutional leanness (CL) and children with normal body weight, and to describe the within-family clustering of CL. We have studied 18 children and teenagers with CL, 10 girls and 8 boys, and 18 gender and age matched normal controls, with the same pubertal stage. All were recruited from the outpatient pediatric clinic nutrition unit. None of the children with CL showed symptoms of chronic illness, they had normal laboratory results, they had a normal caloric food intake, and they did not agree with the DSM-IV-TR criteria for anorexia nervosa. We describe the body mass index (BMI) of children and their parents. The children were classified according to Cole's recently published BMI cut-offs for thinness: under 18.5 points in CL group, stable at least in the last year, and between 18.5 and 25 cutt-offs in the control group. The body composition was calculated by anthropometric methods (skinfold thickness measurements). In addition REE was measured using fasting indirect calorimetry. The CL group had a higher mean percentage of FFM, and a mean FM significantly less, relative to controls (p < 0.001). The average absolute REE was significantly lower in the CL group (1,106.55 ± 240.72 kcal) than the control group (1,353.33 ± 270.01 kcal/dia) (p < 0.01). However, the REE adjusted for FFM showed a mean significantly greater in the CL group (41.39 ± 2.26 kcal/kg FFM) (Mean confidence interval (CI) 95 %: 40.33-42.45) than the controls (37.37 ± 3.06 kcal/kg FFM) (Mean CI 95 %: 35.93-38.81) (p < 0.001). Finally, in the family study, the mean BMI of fathers of CL group was significantly lower (p < 0.01), but there were not any differences in the mean BMI of mothers. Among parents with BMI known, 8 of 35 parents of CL group had an BMI lower 18.5, and only 2 of 36 parents in the control group (p < 0.05). This increased energy expenditure-to-FFM ratio differentiates between CL and controls. These metabolic differences are probably genetically determined.

Misinterpretation of REE data in childhood

IntroductionInflammation is thought to place a metabolic burden on the body which can be detected by raised resting energy expenditure (REE). Increased REE unmatched by dietary intake is frequently implicated...

Use of Bioelectrical Impedance Analysis and Anthropometry to Measure Fat‐free Mass in Children and Adolescents With Crohn Disease

To investigate the precision of published prediction equations for fat-free mass (FFM) from bioimpedance measurements in children with Crohn disease using dual-energy X-ray absorptiometry (DXA) as an in vivo gold standard. Fat-free mass of 49 white boys and girls ages 7.3 to 16.9 y suffering from Crohn disease was measured by DXA. Body weight, height and bioimpedance measurements were also collected. FFM measured by DXA (FFM(DXA)) was compared with FFM predicted by the only 5 published prediction equations available for children and adolescents. An equation was developed for predicting FFM and was validated using a bootstrap method. When correlating predicted FFM with FFM(DXA), Schaefer's equation showed the highest R2 (0.950), the smallest standard error of estimate (SEE) (2.05 kg) and the smallest percentage error (0.28%). Our prediction equation for estimating FFM was FFM = 0.652 Ht2/Z + 0.0385 Wt + 0.586 Age - 0.327, R2 = 0.951, SEE = 2.08, P < 0.0005, where Ht2/Z is the impedance index in cm2/ohm, Wt is body weight in kilograms, age is in years. R2 value from bootstrap method was 0.950 +/- 0.01 (95% confidence interval 0.927-0.968), indicating an acceptable validation of the derived formula. The formula of Schaefer is the best for predicting FFM. The present study provides a new prediction equation for estimating FFM in children with Crohn disease that may be used in clinical settings in which more sophisticated body composition measuring equipments are not available.

Predicting fat-free mass in children using bioimpedance analysis.

Body composition assessment is a useful procedure for the study of nutritional status and water distribution. In adults, it is a predictor of morbidity and mortality, since body fatness is associated with risk factors for cardiovascular disease. Bioelectric impedance analysis (BIA) is a simple, safe, and inexpensive method for assessment of body composition both in pediatric and adult subjects. The aim of our study was to validate the impedance index, ZI (H(2)/Z, height in cm(2)/impedance), as a predictor factor of fatfree mass (FFM) and fat mass (FM) in a sample ( n=75) of normal children. Dual-energy X-ray absorptiometry (DXA) was chosen as reference method. Despite some minor bias, DXAis considerably less expensive and easier to administer in pediatric subjects than other established gold standard reference methods for assessing body composition. ZI values were highly correlated with FFM measured with DXA. The following equations were obtained from the regression analysis: (a). male subjects, FFM(DXA)=0.6375 (ZI)+5.9913, r(2)=0.897, p<0.0001; (b). female subjects, FFM(DXA)=0.7597 (ZI)+ 3.5853, r(2)=0.903, p<0.0001. These data support the notion that BIA alone can be used as a surrogate to measure FFM in a pediatric sample.

Body Composition, Dietary Intake, and Energy Expenditure in Nonobese, Prepubertal Children of Obese and Nonobese Biological Mothers

Objective To determine differences in dietary intake, resting energy expenditure, activity level, fat-free mass, and percentage body and abdominal fat in nonobese children of obese mothers compared with nonobese children of nonobese mothers. Design Cross-sectional comparison study. Children's food diaries were analyzed to determine average energy and nutrient content. Resting energy expenditure of children was measured by means of indirect calorimetry. Children's activity levels were estimated through questionnaires administered during interviews. Dual-energy x-ray absorptiometry was used to estimate body composition of children. Subjects Mothers of subjects responded to advertisements and were recruited as nonobese (body mass index=20 to 25) or obese (body mass index ≥30). Offspring included in the study were prepubertal and nonobese (10th to 90th percentile of weight for height by gender). Twelve pairs of children could be matched for weight, gender, and age. Statistical analysis performed Wilcoxon signed rank tests were used to determine differences between the 2 groups of children. Results Percentage abdominal fat was greater (median difference=3.15, P=.001) and fat-free mass was lower (median difference=1.19, P=.04) in children of obese mothers compared with children of nonobese mothers. No statistically significant differences between the 2 groups of children were found for dietary intake, resting energy expenditure, activity level, or percentage body fat. Applications/conclusions The significantly higher percentage of abdominal fat and lower fat-free mass in children of obese mothers may contribute to obesity onset. Use of dual-energy x-ray absorptiometry as a screening tool for nonobese, prepubertal children with an obese parent will help to identify those at risk. Education and lifestyle changes can then be implemented to help prevent the onset of obesity. J Am Diet Assoc. 1999;99:58-65.

Body measurement variability, fatness, and fat-free mass in children 8, 11, and 14 years of age: Project HeartBeat!

Project HeartBeat! is a four year mixed-longitudinal study of the development of cardiovascular risk factors in White and African American children who at baseline comprised three age cohorts 8, 11, and 14 years. This paper focuses on the anthropometric variables which were chosen to reflect body fat and fat-free mass. Selected anthropometric dimensions are compared with those of samples from the combined National Health and Nutrition Examination Surveys I and II to explore the similarities of the samples in terms of central tendencies and variances. The measurements were then explored in terms of their ability to estimate the two compartment model of body composition: fat-free mass (FFM) and body fat (BF) from bioelectrical impedance (BIA). Project HeartBeat! children are slightly larger than NHANES children and have variances that are generally comparable to the national surveys. Over seven percent (7.7%) of children were overweight (BMI) and 25% had 'mild obesity' by %BF. Three different factor analytic methods (incomplete principal components, alpha and maximum likelihood) produced two latent variables from 17 anthropometric dimensions which together accounted for 76-83% of the variation: (1) A body mass factor (F1) which was weighted highly on six circumferences, weight and six skinfolds, and (2) a linear growth factor (F2) which was strongly associated with height, arm length, and sitting height. Triceps, subscapular and midaxillary skinfolds were consistently highly loaded on the body mass factor and their sum was highly correlated to %BF and fat mass (0.90-0.99). This suggests that this sum could be used to estimate fatness in children in studies where the BIA or other body composition techniques are unavailable. FFM and %BF were predicted from the anthropometric factors. Both factors contributed to the estimate of FFM (R(2) = 0.81-0.93), although F2 contributed proportionately more. The 'body mass' factor (F1) was the main predictor of %BF (R(2) = 0.86-0.93), though at some ages the linear factor (F2) was significantly and negatively related to %BF. This set of anthropometric dimensions, taken for the purpose of estimating body composition and summarized as two latent vectors by factor analysis, strongly reflects body fat and FFM in children and adolescents. Am. J. Hum. Biol. 11:69-78, 1999. Copyright 1999 Wiley-Liss, Inc.

Intima-media thickness and diameter of carotid and femoral arteries in children, adolescents and adults from the Stanislas cohort: effect of age, sex, anthropometry and blood pressure.

To study carotid and femoral intima-media thicknesses and diameters in relation to age, sex, morphologic status and blood pressure. The subjects were 369 men and women (aged 10-54 years) from the Stanislas cohort, with no known cardiovascular disease. Intima-media thicknesses and diameters were measured by B-mode ultrasonography. The effects of sex, age, smoking, anthropometric variables, cholesterol and blood pressure were studied using bivariate and regression analysis. Carotid and femoral intima-media thicknesses were not affected by age nor by sex up to 18 years of age. Thereafter, they increased sharply in men and remained higher than in women. Values were correlated with systolic blood pressure only in men, and with fat-free mass in children and young adults only at the femoral site. Smoking, body mass index and fat mass were associated with intima-media thicknesses only in adults. Carotid diameter was little affected by age during childhood and in adults. Femoral diameter increased up to the age of 18 in both sexes and remained unaffected by age thereafter. This increase was more pronounced in boys, and so values became consistently greater in males aged over 14 years. Carotid diameter was correlated with body mass index or fat mass whereas femoral diameter was correlated with weight or fat-free-mass in children and men. The opposite was observed in women. Sex differences occur before adolescence for arterial diameter, but only at an adult age for intima-media thickness. In young subjects, carotid geometry seems to be influenced by blood pressure and excess body weight, while femoral artery geometry seems to be related to blood pressure and body growth.

Determination of body composition in children and adolescents: validation of bioelectrical impedance with isotope dilution technique.

The determination of body composition as part of the clinical and auxologic follow up of childhood growth disorders necessitates the use of a quick, portable, reliable and simple non-invasive method. The present study was undertaken to validate bioelectrical conductance, height2/resistance (Ht2/R), against isotopically determined total body water (TBW) using heavy water tracer H2[18O]. The subjects (n = 56) consisted of normal children, children with various endocrine disorders, and young adults between the ages of 8-26 years. Isotopically determined TBW and fat free mass (FFM) were highly correlated with Ht2/R (r = 0.94, p = < 0.001, and r = 0.94, p = < 0.001, respectively). In a multiple regression analysis, 96% of the variability in FFM in normal subjects could be predicted by the following equation: FFM = 0.524 Ht2/R + 0.415 Wt-0.32, while in the group of patients by FFM = 0.659 Ht2/R + 0.254 Wt + 2.851. These data suggest that bioelectrical impedance measurements give valid and reliable estimates of FFM in children and adolescents. This easy technique could be incorporated in the auxologic follow up of children on hormone therapy.

American medicine--socialize or capitalize?

Despite the increasing use of tetrapolar whole-body bioelectric impedance (BI) analysis in the assessment of body composition, its usefulness in estimating fat-free mass (FFM) has not been evaluated in comparison with conventional skinfold anthropometry in children. We therefore compared 1) the intraobserver and interobserver reproducibility of BI and skinfold measurements and the derived FFM estimates, and 2) the predictability of FFM as calculated from measurements of total body potassium (TBK) using 40K spectrometry by equations based on either BI or skinfold measurements in 112 healthy children, adolescents, and young adults aged 3.9 to 19.3 y. A best-fitting equation to predict TBK-derived FFM from BI and other potential independent predictors was developed and cross validated in two randomly selected subgroups of the study population by stepwise multiple regression analysis. Although the technical error associated with BI measurements was much smaller than that of skinfold measurements, the reproducibility of BI-derived FFM estimates (intraobserver coefficient of variation [CV], 0.39%; interobserver CV, 1.23%) was only slightly better than that of FFM estimates obtained by use of weight and two skinfold measurements (0.62% and 1.39%, respectively). The cross validation procedure yielded the following best-fitting prediction equation: FFM = 0.65 x (height2/impedance) + 0.68 x age + 0.15 (R2 = 0.975, root mean square error = 1.98 kg, CV = 5.8%, 95% limits of agreement = -11.1% to +12.4%). Conventional anthropometry, using published equations to estimate FFM from skinfolds, slightly over-estimated TBK-derived FFM, but predicted FFM with precision similar to the best-fitting equation involving BI. Previously published FFM equations incorporating BI predicted TBK-drived FFM with variable predictive precision and accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Fat-free mass in children and young adults predicted from bioelectric impedance and anthropometric variables

Fat-free mass (FFM) values calculated from densitometry by using a multicomponent model were significantly (p less than 0.05) larger than those from the Siri two-component model (465 males, 441 females), especially in children and females. The multicomponent model assumes the density of FFM varies by age and sex because of differences in its constituents. With FFM values from the multicomponent model as the dependent variable and impedance and anthropometry as the independent variables, prediction equations were derived by all possible subsets of regression (140 males, 110 females). These equations had RMSEs of 2.2-2.3 kg and CVs of 5.0-5.8%. Cross-validation results were excellent for young adults but less satisfactory for children for whom a different calf skinfold had been measured. The selected equations are applicable to healthy white individuals aged 7-25 y.