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Home Loan Comparison Spreadsheet – Introduction: Determine body composition changes in adiposity can assess an individual.
Objective: The objective of this study was to evaluate total body fat percentage based on two and four compartment models in obese Chilean school children, adjusting for differences in sex and puberty status.
Methods: Sixty-one obese school children (33 boys and 28 girls) between 8 and 13 years of age were evaluated. Two compartment measurements of body fat percentage considered isotope dilution, plethysmography, radiographic absorptiometry and bioelectrical impedance; Using the four compartment model as a benchmark.
Results: Each method explained between 43-87% of the variance in body fat percentage in Tanner stage I and II children and between 78-96% in Tanner stage III and V children. In both groups of children differed significantly for stage I, with the exception of plethysmography. High R2 values ​​were observed for girls in all Tanner stages. Each method explained between 34-92% of the variance in body fat percentage for girls in stages I and II and between 63-93% for stages III and V. In obese boys, R2 values ​​were high for stages III and V. In girls And boys in Tanner stage III and V, the smallest differences are observed for isotopic dilution, and DXA (dual-energy X-ray absorptiometry) scan for stages I and II.
Conclusions: For obese boys and girls, the two compartment model with isotopic dilution and DXA had the best precision and smallest differences in determining body fat percentage compared to the benchmark

Key words: Body fat percentage. Four compartment model. Two compartment model. Isotopic dilution. Radiographic absorptiometry. Plethysmography. Bioelectrical impedance.


Introduction: determining the body composition allows to evaluate changes in the adiposity of an individual.
Objective: The objective of this study was to evaluate total body fat based on two compartment models (2C) and to compare them with the four compartment model (4C) in obese Chilean schoolchildren, considering potential differences by sex and pubertal development.
Methods: 61 obese schoolchildren (33 boys and 28 girls) between 8 and 13 years old. The measurement of body fat by 2C considered isotopic dilution, plethysmography, radiographic absorptiometry and bioimpedanciometry; Using the 4-compartment model as the reference standard.
Results: Each method accounted for 43-87% of the variance to determine the percentage of body fat in stage I and II children and 78-96% in stage III and IV. In both groups of children, slopes differed significantly in stage I, with the exception of plethysmography. In girls, high R2 values ​​were observed at all stages of pubertal development. Each method accounted for 34-92% of the variance to determine the percentage of body fat in stage I and II girls and 63-93% in stage III and IV, respectively. In obese children, R2 values ​​were high, mainly in the stage III and IV group. In boys and girls of Tanner III and IV, the smallest differences with the reference standard were with isotope dilution; As for Tanner I and II, the smallest differences were obtained with DEXA.
Conclusions: In both sexes, the two-compartment model with isotope dilution and DEXA had the highest accuracy and the smallest differences to determine body fat in obese children and adolescents, as compared to the reference standard.

Key words: Percentage of body fat. Four-compartment model. Two-compartment model. Isotopic dilution. Radiographic Absorciometry. Plethysmography. Bioimpedanciometry.



The prevalence of obesity in Chilean school children is 25.3%, with slightly higher levels among boys compared to girls (28.3% vs. 22.3%) (1). Increases in adiposity associated with childhood obesity are a risk factor for glucose intolerance, insulin resistance, dyslipidemia, non-alcoholic fatty liver disease, hypertension, heart attack, stroke and premature death (2-6). Although body mass index (BMI) is widely used as an index of body fat (BF), it is not a direct measurement of adiposity. BMI can not distinguish between different types of body mass (e.g., fat mass, fat free mass, bone mass), thus the use of BMI can lead to errors in the estimation of BF, especially in the context of obesity. Changes in weight and height associated with normal growth are responsible for a 50% increase in BMI, which further complicates the interpretation of this index for children and adolescents. The increase in BMI during adolescence is primarily a result of an increase in fat free mass (7,8). BMI is a global indicator of nutritional status and does not distinguish between lean and fat mass (9). Thus, measuring fat mass would allow for the quantification of metabolic risk associated with an increase in obesity.

In the classic two compartment model of body composition, body weight is divided into fat mass and fat free mass. This model is widely used for clinical practice and nutritional follow-up. BODPOP uses the relationship between pressure and volume to calculate body volume and density (10) Isotopic dilution quantifies total body water, which can be used to predict fat free mass, as a proportion of water known in fat free mass by age and sex (11 ) DXA differentiates between fat and fat free mass based on the differential attenuation of x-rayes (12). Bioelectrical impedance, BIA, is an indirect method to measure the total body water and fat free mass (13).

The most precise method, considered the gold standard, for determining body composition is the four compartment model. For this method, fat free mass is divided into water, minerals and proteins (10). Although multi-compartment models of body composition have better accuracy, few studies have used them to validate simpler methodology in obese children and adolescents (14). The current study aimed to determine the predictive capacity of the two compartment model of BF% (body fat percentage) compared to the four compartment model in a sample of obese Chilean school children, adjusting for possible differences by sex and pubertal stage.




We worked with a sample of 61 obese children years (males = 33 and females = 27) between 8 and 13, from a school in the Macul neighborhood of Santiago, Chile. The school was chosen for convenience, given the proximity of the school to the place of measurements. Inclusion criteria included: BMI ≥ 95th percentile according to CDC-NCHS references (15), full-time attendance at an educational institution, parental consent and child assent. The exclusion criteria included: medical diagnosis of psychomotor disorder, use of drugs that can alter body composition, performing physical activity, and / or biochemical parameters. This research was approved by the Ethics Committee of the University of Chile.


Pubertal development was classified using Tanner staging, considering breast development in females and genital in males (16). Developmental stages were determined by visual inspection during physical examination by a pediatrician.


Weight and height were assessed in the morning after an overnight fast. Children wore minimal clothing, standing in front of the scale, with feet together at the center of it, arms attached to the body, the head forming a straight line parallel to the floor to join the corner of the eye and the birth of the ear . An electronic balance (SECA® Model 767) was used with sensitivity of 10 grams for weight and Holtain stadiometer (SECA) with sensitivity 0.1 cm for height, both imported by Precision Hispana. Four skin folds (biceps, triceps, subscapular and suprailiac), with a Lange caliper millimeter (1 mm), were assessed in triplicate using the technique described by Lohman et al. (17).


Total body water was determined with deuterium dilution. The isotope (4 grams of deuterium oxide 99.8%) was administered orally according to body weight of the subject. The amount of body water was measured by determining the concentration of deuterium oxide, according to the Plateau method. This required that the subjects were in total fasting for a period of three hours, which corresponds to the period of equilibrium and minimizes changes in total body water content (11). After the fast, the saliva sample (2 mL, baseline) was taken. Subsequently, the deuterium dose and an additional 20 ml of tap water were given to ensure dose ingestion. After three hours, during which participants were not allowed to urinate, eat or drink anything additional, the second saliva sample (post dose) was taken and frozen at -20 oC. For analyzing the concentration of deuterium in saliva, the sample was thawed, equilibrated in hydrogen gas, adding 5% platinum on aluminum with time of three days to reach equilibrium. The deuterium / hydrogen ratio in the gas released was analyzed by mass spectrometry (Hydra, Europe Scientific, Crewe, Cheshire, United Kingdom).


Volume and body density were measured with an air displacement plethysmograph (BODPOD, mod 2000, Life Measurement, Inc., Concord, USA). Children were tested with underwear, without metal objects and a swimming cap to compress the hair. Later, children were weighed on a calibrated scale with an accuracy of 5 g. The system performs a pressure measurement with the empty chamber, then the equipment is calibrated using a 50 liter calibration cylinder, after which the subject is measured 2-3 times. Body size obtained by this method was used for the 4C (four compartment) equation.


Bone mineral density was estimated using dual energy x-ray absorptiometry using Lunar Prodigy Ghc DPX-NT (Lunar Radiology, WI, USA) technology, which assesses the entire body in a five-minute sweep. Children were placed supine wearing a light robe.


Bioelectrical impedance was measured using Tanita BC-418MA, eight-electrode, hand-to-foot system, manufactured by the Tanita Corporation (Tokyo, Japan). Measurements were collected according to manufacturer’s guidelines using a 50 kHz frequency. Height, sex and age were entered manually, whereas weight was recorded automatically. Measurements were taken in the morning after physical exercise and empty bladders.


The 4C model divides the body in fat, water, protein, and minerals (18-20). The ability of the model to adjust core body mineral mass results in a more accurate estimate of hydration and lean mass density compared to the 3C model. The 4C model is considered the “gold standard” because it takes into account the variability of its components. The equation has been validated in children of the same group (21).

The 4C equation used was a follows:

BF (kg) = [(2.747 * BV) – (0.710 * TBW)] + [(1,460 * BMC) – (2.050 * W)]

BV = body volume in liters (plethysmography), TBW = total body water in liters (isotope dilution), BMC = bone mineral content in kg. (DXA) and W = body weight (kg).


Descriptive statistics were used: minimum, maximum and frequency tables. Continuous variables were analyzed with the goodness of fit test of Shapiro Wilk test of homogeneity of variance. For variables that met normality assumptions we reported the average and standard deviation, otherwise the median and interquartile range were shown. Differences by gender and pubertal development were analyzed using Student’s t test.

Each of the methods (isotopic dilution, DXA and plethysmography BIA) were compared with the results of the 4C model. This comparison was made using the Lin (22) concordance coefficient and Bland-Altman method (23). The Bland-Altman analysis was calculated as the mean difference between the reference (4C model) and each of the methods and the 95% distribution (confidence intervals).

The regression analysis was done to compare the 4C model and the simplest methods (isotope dilution, DXA, plethysmography and BIA) for determining BF%. The slopes and intercepts were assessed and the standard error of the estimate (SEE) was calculated. P <0.05 was established as the cutoff for statistical significance. The study data were analyzed using STATA program version 10.1 (24).



Physical and body composition of the sample by gender and pubertal development are shown in table I. There was no interaction between sex and pubertal development. However, several significant sex differences were found. Boys had significantly higher values ​​in the variables: age, weight, height, total body water and bone mineral density. As well, in body composition for both BF (kg) and (fat free mass) FFM in kg and percentage for the 4C model, isotopic dilution, DXA, BIA and plethysmography. Also, boys had higher values ​​in the determination of BF% by BIA. Similarly, there were significant differences associated with pubertal development. Both males and females with advanced puberty, showed significantly higher results in age, weight, height, total body water and bone mineral density. BF (kg) and FFM (kg) in the 4C model, isotope dilution, DXA, BIA and plethysmography. Lean mass (%) for boys only in the BIA and 4C model. Girls with pubertal development I and II had significantly higher FFM values ​​(%).

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