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.

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...