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.

Central obesity and body fat, but not body mass index, are associated with the Pro12Ala polymorphism in the peroxisome proliferator-activated receptor γ gene in a population with a high consumption of saturated and trans-fatty acids.

The relationship of the Pro12Ala polymorphism in the peroxisome proliferator-activated receptor γ (PPARγ) gene with obesity and its modulation by dietary fat has been proposed, but the few studies addressing this issue have yielded controversial results. In a Mexican population characterized by high-fat consumption, we hypothesized that the Pro12Ala PPARγ genotype is related to obesity and this relationship is modulated by intake of saturated fatty acids (SFAs) and trans-fatty acids (TFAs). We recruited 69 adults for this cross-sectional study. The Pro12Ala PPARγ polymorphism was determined from blood genomic DNA by using real-time polymerase chain reaction. Univariate and multivariate logistic regression analyses were performed. Pro12Ala showed a positive association with central obesity (adjusted odds ratio, 7.38; 95% confidence interval, 1.19-45.77; P = .032) and percentage of body fat (%BF; adjusted odds ratio, 1.08; 95% confidence interval, 1.00-1.17; P = .048), suggesting that Pro12Ala carriers are more likely to have central obesity and a higher %BF than Pro12Pro carriers. A modifying effect was observed for the SFAs strata: we found a significant association between the Pro12Ala polymorphism and %BF in the high-SFA-intake stratum (P < .04), but not in the low-intake stratum (P > .7). No modifying effect was observed for the TFAs strata. In addition, the impact of total energy intake on obesity in Pro12Ala carriers seemed to be stronger than that in the wild-type genotype carriers. As hypothesized, our data demonstrated a relationship between the Pro12Ala PPARγ polymorphism and the presence of obesity, which is modulated by SFA intake but not TFA intake.