Over the last decades, there has been a worldwide growing prevalence of overweight and obesity among people of all ages [
Given the major short- and long-term consequences of childhood obesity on health, well-being, and costs to health care and social security systems, as well as the better chances for intervention at young ages, public and private funding agencies should give a high priority to research on obesity in children and adolescents [
To this end, a set of techniques are used to assess obesity such as isotope dilution and dual energy X-ray absorptiometry (DEXA). These techniques offer accurate measurement of adiposity but they are expensive and cannot be used everywhere [
A number of studies have explored the relationship between BMI and adiposity measures and showed high degree of correlation between them in children and adolescents [
The goals of this study were to assess, for the first time in Morocco and North Africa: (a) the relationship between body fat, assessed by isotope dilution technique, and each of BMI and WC in adolescents, and (b) the effectiveness of fat mass (FM), percent body fat (PBF), BMI, and WC to predict adolescents with high-blood glucose level as health risk related to excess body fat.
The study was carried out in Rabat region (Morocco) after receiving the institutional approval from the Ministry of National Education. A total of 167 adolescents (123 girls and 44 boys) aged 11–17 years were recruited from seven randomly selected secondary schools. The adolescents who participated in the study were selected by their teacher based on their weight status (overweight/obese and normal weight). A written consent was obtained from the parents or tutors, and verbal consent was provided by each subject. Anthropometric measures, saliva, and blood samples were taken at schools. Fat mass, percent body fat and fasting blood glucose level were determined at the laboratory of “Unité Mixte de Recherche en Nutrition et Alimentation, URAC39 (Université Ibn Tofaïl-Centre National de l’Energie, des Sciences et Techniques Nucléaires-CNESTEN-Rabat).”
Anthropometric measurements were taken by trained operators using standard equipments. Body weight was measured to the nearest 0.1 Kg using portable scale (Seca, Germany) with minimal clothing and no shoes. Height was measured to the nearest 0.1 cm using a height bar (2 meters, dismantling) without shoes. BMI was calculated as weight in kilogram divided by the square of height in meter (Kg/m2). WC was measured to the nearest 0.1 cm in standing position at the midpoint between the lowest rib and the iliac crest and at the end of normal expiration, using a measuring tape.
Using these measurements and the new WHO growth reference 5–19 years [
In our study, FM and PBF were estimated from total body water (TBW). TBW was determined by isotope dilution technique using the deuterium oxide (2H2O). Naturally, the body water pool contains a small amount of deuterium (2H). This represents the natural abundance of 2H in body water. When 2H is ingested, it mixes with body water within a few hours. The amount of deuterium in body water above that naturally present is known as the enrichment of body water that reaches a “plateau” after 3–5 hours [
In this study, we used the hydration factors (see Table
Hydration factor of fat-free mass in children and adolescents.
Age (years) | Boys | Girls |
---|---|---|
11-12 | 75.4 | 76.6 |
13-14 | 74.7 | 75.5 |
15-16 | 74.2 | 75.0 |
17–20 | 73.8 | 74.5 |
All subjects had fasted for 12 hours prior to blood draw. Blood samples were stored in ice till the delivery to the laboratory (within 4 hours), and subsequently stored at −80°C until analysis. Fasting blood glucose (FBG) concentration was measured using the glucose hexokinase methodology [
Means and standard deviations were calculated for each variable using descriptive statistics. Two-way ANOVA was used to examine the effect of gender, weight status, and their interaction. Pearson’s correlation was used to assess the relationship between body fat (FM and PBF) and each of BMI and WC, and their association with FBG. All statistical analyses were performed using SPSS (statistical package for social sciences, version 17.0). The Kolmogorov-Smirnov normality test was used to determine whether data set was well modeled by a normal distribution or not.
A total of 167 adolescents participated in the study. 42% were overweight or obese and 58% had normal weight. Since the number of obese and overweight subjects was low, boys and girls of the study sample were divided into two groups (normal weight and overweight-obese). The mean and standard deviations (SD) of age, weight, height, BMI, WC, FM, PBF, and FBG are presented in Table
Characteristics of study sample (mean ± SD) and main effect of gender, weight status, and their interaction (two-way ANOVA).
Variables | Gender | Total | Normal weight | Overweight-obese | |||
Boys: | Boys: | Boys: | Effect of gender | Effect of weight status | Effect of interaction between gender and weight status | ||
Age, years | Boys | 14.19 ± 0.93 | 14.44 ± 0.83 | 14.03 ± 0.96 | 0.559 | 0.997 | 0.041 |
Girls | 14.29 ± 1.18 | 14.15 ± 1.15 | 14.57 ± 1.21 | ||||
Weight, kg | Boys | 61.64 ± 13.23 | 55.0 ± 10.0 | 65.80 ± 13.49 | 0.185 | <0.0001 | 0.005 |
Girls | 54.45 ± 13.28 | 47.4 ± 7.3 | 67.93 ± 11.52 | ||||
Height, m | Boys | 1.62 ± 0.11 | 1.65 ± 0.11 | 1.60 ± 0.11 | 0.012 | 0.284 | 0.019 |
Girls | 1.58 ± 0.07 | 1.58 ± 0.08 | 1.60 ± 0.06 | ||||
BMI, kg/m² | Boys | 23.49 ± 3.96 | 20.12 ± 2.27 | 25.61 ± 3.27 | 0.893 | <0.0001 | 0.025 |
Girls | 21.62 ± 4.47 | 19.02 ± 2.07 | 26.58 ± 3.49 | ||||
WC, cm | Boys | 81.27 ± 11.98 | 72.4 ± 8.4 | 86.83 ± 10.52 | 0.472 | <0.0001 | 0.222 |
Girls | 75.38 ± 11.76 | 69.3 ± 7.7 | 86.98 ± 9.08 | ||||
FM, kg | Boys | 18.71 ± 10.48 | 10.64 ± 5.92 | 23.79 ± 9.53 | 0.054 | <0.0001 | 0.840 |
Girls | 17.41 ± 8.90 | 12.87 ± 4.67 | 26.07 ± 8.66 | ||||
PBF, % | Boys | 29.27 ± 12.46 | 19.08 ± 9.92 | 35.68 ± 9.26 | 0.001 | <0.0001 | 0.073 |
Girls | 30.48 ± 8.92 | 26.63 ± 6.59 | 37.83 ± 8.18 | ||||
FBG, g/L | Boys | 0.92 ± 0.14 | 0.89 ± 0.11 | 0.94 ± 0.15 | 0.306 | 0.182 | 0.195 |
Girls | 0.89 ± 0.11 | 0.89 ± 0.10 | 0.89 ± 0.12 |
BMI: body mass index (kg/m²); WC: waist circumference (cm): FM, fat mass (kg): PBF, percent body fat (%): FBG: fasting blood glucose (g/L).
Table
Pearson’s correlation coefficients (
BMI | WC | |||
FM | PBF | FM | PBF | |
Boys | ||||
Total ( | 0.850** | 0.711** | 0.717** | 0.575** |
Normal weight ( | 0.770** | 0.648** | 0.513* | 0.347 |
Overweight-obese ( | 0.739** | 0.413* | 0.571** | 0.289 |
Girls | ||||
Total ( | 0.896** | 0.724** | 0.824** | 0.677** |
Normal weight ( | 0.690** | 0.505** | 0.626** | 0.434** |
Overweight-obese ( | 0.799** | 0.488** | 0.628** | 0.404** |
*Correlation is significant at
**Correlation is significant at
On the other hand, WC showed significant positive correlation with FM in both genders of the study sample (boys,
Overall, the relationships of BMI and WC with each of FM and PBF were found to be dependent on gender and weight status. The relationship between BMI and PBF was stronger in overweight-obese girls than overweight-obese boys. Similarly, the relationship between WC and PBF was stronger in both normal weight and overweight-obese girls than normal weight and overweight-obese boys. On the other hand, the association of BMI and WC with FM was observed to be more significant than with PBF mainly in overweight-obese boys.
Table
Pearson’s correlation coefficients of FBG with FM, PBF, BMI, and WC.
FBG | ||||
FM | PBF | BMI | WC | |
Boys | ||||
Total ( | 0.121 | 0.155 | 0.193 | 0.214 |
Normal weight ( | 0.180 | 0.103 | 0.273 | 0.214 |
Overweight-obese ( | −0.049 | 0.005 | 0.026 | 0.270 |
Girls | ||||
Total ( | 0.241** | 0.246** | 0.094 | 0.090 |
Normal weight ( | 0.076 | 0.105 | −0.036 | −0.142 |
Overweight-obese ( | 0.583** | 0.561** | 0.330* | 0.528** |
*Correlation is significant at
**Correlation is significant at
Dependent variable: FBG.
BMI is commonly used as an indicator of overall obesity in adults due to its simplicity and correlation with percent body fat [
Our results showed a high significant relationship between BMI and each of FM and PBF in both boys and girls. These results are in agreement with previous studies, suggesting that BMI is highly related to adiposity and may be useful in identifying excess body fat in children and adolescents [
A number of studies have reported the strong positive correlation between WC and body fat [
WC was found to be closely associated to FM and PBF in both boys and girls of the study sample, and in normal weight and overweight-obese girls. Our results are consistent with those of previous studies which suggest WC as a good diagnostic test for fatness in adolescents [
The current study aimed to test the effectiveness of FM, PBF, BMI, and WC in predicting high levels of FBG as health risk related to excess body fat in adolescents. Many studies support the hypothesis that the relationship between adiposity and risk of disease begins early in life [
Our results showed high positive association of FBG with FM and PBF in girls of the study sample and in overweight-obese girls as well. Similar positive association of FBG with BMI and WC was observed in overweight-obese girls. Our findings are in line with available data from previous studies on the relationship between adiposity and blood glucose level. It has been reported that the level of FBG was found to be higher in overweight and obese children compared to the normal children [
On the other hand, there was no significant correlation between FBG and BMI, WC, FM, and PBF in boys, may be due to the small sample size.
Our study had some limitations such as the small size of the whole sample and weight status groups particularly for boys. Our ability to recruit more subjects was hampered by the surge of influenza A/H1N1 during the course of the study. Also the authorization to access to schools has not been renewed by the concerned authorities for 2010-2011 academic year.
Another limitation is that the relationship between adiposity measures and each of BMI and WC, in one hand, and between FBG and other variables, on the other hand, may depend on pubertal stages (PS) that were not addressed in our study. For instance, it was observed in a previous study that the relationship between WC and PBF changes with sexual maturity, and that the normal pattern from PS1 to PS5 is for PBF to decrease and WC to increase [
BMI and WC were closely associated with FM and PBF, derived from isotope dilution technique, in a sample of Moroccan adolescents from Rabat. It should be noted, however, that these associations depend on gender and weight status, and that BMI may provide a better proxy estimate of overall obesity than WC. Nevertheless, both of them appear to be reasonable surrogate for FM and PBF, particularly in epidemiological studies, as screening tools to identify adolescents at increased risk of developing excess body fat and high levels of fasting blood glucose.
Further research is needed for this group of population and should include (1) studies to confirm our results taking into account the puberty stage, (2) investigation of the association of overall and central obesity with fasting blood glucose level among girls in different age or ethnic groups and the mechanism that produces the gender difference observed in the current study, and (3) relationship of BMI, WC, FM, and PBF with other metabolic abnormalities for early prevention of health risks related to overweight and obesity.
Body mass index
Centre National de l’Energie, des Sciences et Techniques Nucléaires
Fasting blood glucose
Fat-free mass
Fat mass
Fourier transform infrared spectroscopy
Percent body fat
Total body water
Waist circumference
World Health Organization.
All authors declare having no conflict of interest.
The authors thank the volunteers who participated in the present study and all who contributed in data collection mainly Professors N. El Haloui and A. Derouiche, Ph.D. students (N. Attalhi, G. Choua, H. Labraimi, E. Aglago, K. Janah, …) and medical staff (Dr. H. Belghiti and Dr M. Azelaf, …). They also thank the International Atomic Energy Agency for its funding and technical assistance.