External validation of a prediction model for estimating fat mass in children and adolescents in 19 countries: individual participant data meta-analysis.

OBJECTIVE: To evaluate the performance of a UK based prediction model for estimating fat-free mass (and indirectly fat mass) in children and adolescents in non-UK settings. DESIGN: Individual participant data meta-analysis. SETTING: 19 countries. PARTICIPANTS: 5693 children and adolescents (49.7% boys) aged 4 to 15 years with complete data on the predictors included in the UK based model (weight, height, age, sex, and ethnicity) and on the independently assessed outcome measure (fat-free mass determined by deuterium dilution assessment). MAIN OUTCOME MEASURES: The outcome of the UK based prediction model was natural log transformed fat-free mass (lnFFM). Predictive performance statistics of R2, calibration slope, calibration-in-the-large, and root mean square error were assessed in each of the 19 countries and then pooled through random effects meta-analysis. Calibration plots were also derived for each country, including flexible calibration curves. RESULTS: The model showed good predictive ability in non-UK populations of children and adolescents, providing R2 values of >75% in all countries and >90% in 11 of the 19 countries, and with good calibration (ie, agreement) of observed and predicted values. Root mean square error values (on fat-free mass scale) were <4 kg in 17 of the 19 settings. Pooled values (95% confidence intervals) of R2, calibration slope, and calibration-in-the-large were 88.7% (85.9% to 91.4%), 0.98 (0.97 to 1.00), and 0.01 (-0.02 to 0.04), respectively. Heterogeneity was evident in the R2 and calibration-in-the-large values across settings, but not in the calibration slope. Model performance did not vary markedly between boys and girls, age, ethnicity, and national income groups. To further improve the accuracy of the predictions, the model equation was recalibrated for the intercept in each setting so that country specific equations are available for future use. CONCLUSION: The UK based prediction model, which is based on readily available measures, provides predictions of childhood fat-free mass, and hence fat mass, in a range of non-UK settings that explain a large proportion of the variability in observed fat-free mass, and exhibit good calibration performance, especially after recalibration of the intercept for each population. The model demonstrates good generalisability in both low-middle income and high income populations of healthy children and adolescents aged 4-15 years.

The Influence of 2-Year Changes in Physical Activity, Maturation, and Nutrition on Adiposity in Adolescent Youth.

The aim of this longitudinal study was to explore temporal patterns of physical activity (PA) and adiposity in Spanish adolescents. Eighty healthy adolescents were followed over a 2-year period (42 girls and 38 boys). A PA score was estimated using the Physical Activity Questionnaire for Adolescents (PAQ-A). Adiposity was assessed by anthropometric measurements; body mass index (BMI) and fat mass percent (FMP) were calculated using standard equations. Sexual maturity was estimated by percentage of predicted adult stature. Dietary intake was assessed by a self-administered food-frequency questionnaire. Three assessments were performed: September 2011 (S1), 2012 (S2), and 2013 (S3). A repeated-measures ANOVA was conducted to examine temporal changes in PA and FMP and sex change in maturation categories (two factor mixed-design, 2x2x3). A stepwise linear regression was conducted in order to estimate the predictors of FMP change. Significant changes for FMP were found between S1, S2, and S3 (23.41±8.24 vs. 21.89±7.82 vs. 22.05±8.06, p<0.05; respectively); a significant interaction of FMP with sex was observed (F = 4.387, p<0.05 for S2-S3), but not for maturation. PA at S2 was significantly higher than S3 (2.58±0.72 vs. 2.29±0.73, p<0.001). An interaction between PA change and sex was statically significant (F = 4.889, p<0.05 for S2-S3). A reduction in PA was observed after the S2 period without changes in adiposity. In contrast, a significant reduction in FMP was seen between S1 and S2, while PA did not significantly change. There were no significant differences for nutritional variables between S1 and S3, and nutrition was not a determinant of the changes in PA or FMP. Our results suggest that body composition changes observed during adolescence are not driven by changes in PA. Moreover, the interaction analysis suggests that PA behavior is affected by sex, but is not modified by maturation.

Estimaciones de la masa grasa y la masa muscular por métodos antropométricos y de bioimpedancia eléctrica / Assessment of fat mass and skeletal muscle mass by means of conventional anthropometry and bioelectrical impedance analysis

Determinar la masa grasa y sus diferencias estimadas por técnicas de antropometría y bioimpedancia eléctrica de cuerpo entero, así como presentar datos de masa muscular esquelética en jóvenes en edad escolar, por métodos antropométricos. Método: Se ha procedido a la valoración de la composición corporal de 75 niños y 75 niñas de entre 12 y 18 años, mediante técnicas antropométricas y de bioimpedancia eléctrica de cuerpo entero para estimar la masa grasa (Slaughter y Houtkooper, respectivamente), así como la masa muscular esquelética (Poortmans). El análisis estadístico consistió en un estudio comparativo entre métodos que se realizó mediante la prueba de la t de Student, un estudio correlacional mediante el coeficiente de correlación de Spearman, así como un estudio de concordancia entre métodos mediante los procedimientos de Bland-Altman. Resultados: No existen diferencias significativas de la masa grasa determinada por ambos métodos (p > 0.05). Existen diferencias estadísticas en la masa muscular esquelética entre niños y niñas (p < 0.05). El estudio de concordancia muestra pequeñas diferencias entre métodos con errores proporcionales para el grupo de niños, no así en niñas,y con muy amplios límites de concordancia entre métodos. Conclusiones: En general, se puede concluir que la metodología antropométrica y de bioimpedancia eléctrica para la estimación de la composición corporal no son intercambiables para valoraciones longitudinales, en niños en edad escolar de 12 a 18 años, y aunque se observan pequeñas diferencias, existe un efecto de error proporcional entre método...

Validez de los índices de masa corporal y de masa grasa como indicadores de sobrepeso en adolescentes españoles: estudio Esccola / Validity of body mass index and fat mass index as indicators of overweight status in Spanish adolescents: Esccola Study

Objetivo y fundamento: Comprobar la exactitud del índice de masa corporal (IMC), del índice de masa grasa (IMG) y del índice de masa libre de grasa (MLG) para diagnosticar y determinar valores de corte para el sobrepeso en una población de jóvenes adolescentes entre 12 y 18 años de edad. Sujetos y método: Se estudió a 150 niños (75 varones: edad media de 14,81 años [desviación estándar {DE} de 1,86], talla media de 168,8 cm [DE de 8,8], peso medio de 65,84 kg [DE de 16] e IMC medio de 22,89 kg/m2 [DE de 4,4]; 75 niñas: edad media de 14,88 años [DE de 1,94], talla media de 159,4 cm [DE de 7,6], peso medio de 54,77 kg [DE de 9,54] e IMC medio de 21,48 kg/m2 [DE de 3,1]). El porcentaje de masa grasa se determinó mediante el cálculo del agua corporal total con un espectrómetro de masas para razones estables y aplicando las constantes de hidratación de la MLG para cada edad. La definición de sobrepeso se realizó aplicando los valores de porcentaje de grasa de Taylor relativos a cada edad y correspondientes al punto de corte internacional de 25 kg/m2, que clasifica el estado de sobrepeso. Se aplicó un análisis de curvas receiver operating characteristics y se calcularon las áreas bajo la curva de cada índice (IMC, IMG y MLG), así como los valores de sensibilidad y especificidad. Resultados: En los niños, los valores predictivos positivos fueron del 78,1% para el IMC y del 89,2% para el IMG, mientras que para las niñas estos valores fueron del 34,8 y del 81,4%, respectivamente. Los valores predictivos negativos fueron del 81,4 y del 100% en los niños y del 98,1 y del 100% en las niñas para el IMC y el IMG, respectivamente. Las áreas bajo la curva del IMG para los niños (0,988, intervalo de confianza del 95% de 0,930-0,998) y las niñas (0,996, intervalo de confianza del 95% de 0,943-1,000) mostraron una alta capacidad de predicción para el diagnóstico de sobrepeso (AU)

Background and objectives: to determine the accuracy of body mass index (BMI), fat mass index (FMI) and fat-free mass index (FFMI) to find cut-off points related to overweight in adolescents aged 12–18 years.Subjects and method: 150 adolescents were assessed (75 boys aged 14.81±1.86yr, height 168.8±8.8cm, weight 65.84±16kg and BMI 22.89±4.4kg.m2, and 75 girls aged 14.88±1.94yr, height 159.4±7.6cm, weight 54.77±9.54kg and BMI 21.48±3.1kg.m2). Body composition was measured by using the deuterium dilution technique with an isotope ratio mass spectrometer and fat free mass hydration constants were applied.Subjects and method: Taylor's age-related overweight classification was applied and receiver operating characteristic (ROC) curves analyses were performed. Areas under curve were calculated for every index (BMI, FMI and FFMI). Sensitivity and specificity values of BMI and FMI to diagnose overweight were evaluated.Results: Among boys, predictive positive values for BMI were 78.1% and 89.2% for FMI; predictive positive values in girls was 34.8% for BMI and 81.4% for FMI. Predictive negative values were 81.4% and 100% in boys and 98.1% and 100% in girls for BMI and FMI. Areas under curve of FMI for boys (0.988, 95%CI: 0.930-0.998) and girls (0.996, 95%CI: 0.943–1.000) showed high accuracy for overweight diagnose. Cutoff points of 4.58kg.m2 in boys and 7.76kg.m2 in girls for FMI and 23.07kg.m2 in boys and 23.18kg.m2 in girls for BMI had high sensitivity and specificity as indicators of overweight classification

[Validity of body mass index and fat mass index as indicators of overweight status in Spanish adolescents: Esccola Study]. / Validez de los índices de masa corporal y de masa grasa como indicadores de sobrepeso en adolescentes españoles: estudio Esccola.

BACKGROUND AND OBJECTIVES: To determine the accuracy of body mass index (BMI), fat mass index (FMI) and fat-free mass index (FFMI) to find cut-off points related to overweight in adolescents aged 12-18 years. SUBJECTS AND METHOD: 150 adolescents were assessed (75 boys aged 14.81+/-1.86yr, height 168.8+/-8.8cm, weight 65.84+/-16kg and BMI 22.89+/-4.4kg x m(2), and 75 girls aged 14.88+/-1.94yr, height 159.4+/-7.6cm, weight 54.77+/-9.54kg and BMI 21.48+/-3.1kg x m(2)). Body composition was measured by using the deuterium dilution technique with an isotope ratio mass spectrometer and fat free mass hydration constants were applied. Taylor's age-related overweight classification was applied and receiver operating characteristic (ROC) curves analyses were performed. Areas under curve were calculated for every index (BMI, FMI and FFMI). Sensitivity and specificity values of BMI and FMI to diagnose overweight were evaluated. RESULTS: Among boys, predictive positive values for BMI were 78.1% and 89.2% for FMI; predictive positive values in girls was 34.8% for BMI and 81.4% for FMI. Predictive negative values were 81.4% and 100% in boys and 98.1% and 100% in girls for BMI and FMI. Areas under curve of FMI for boys (0.988, 95%CI: 0.930-0.998) and girls (0.996, 95%CI: 0.943-1.000) showed high accuracy for overweight diagnose. Cutoff points of 4.58kg x m(2) in boys and 7.76kg x m(2) in girls for FMI and 23.07kg x m(2) in boys and 23.18kg x m(2) in girls for BMI had high sensitivity and specificity as indicators of overweight classification. CONCLUSIONS: FMI showed high accuracy for overweight screening. Thus, our cut-off points may be useful as a tool to surveillance children's overweight on clinical and epidemiologic settings.