Estudio de la composición corporal en niños y su relación con la actividad física: desarrollo de ecuaciones de predicción de masa grasa y masa libre de grasa
- Autores: Gabriel Omar Tarducci
- Directores de la Tesis: Anabel Nora Pallaro (dir. tes.), Manuel Avelino Giráldez García (dir. tes.), Elvis Álvarez Carnero (dir. tes.)
- Lectura: En la Universidade da Coruña ( España ) en 2013
- Idioma: español
- Número de páginas: 231
- Tribunal Calificador de la Tesis: Manuel Hernández Triana (presid.), Rafael Martín Acero (secret.), Eliseo Iglesias-Soler (voc.), José Ramón Alvero Cruz (voc.), Miguel del Valle Soto (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: RUC
- Resumen
As it is nowadays well recognized, the habits and lifestyles are characterized by an insufficient physical activity, the intake of foods high in calories and low in micronutrients, and by an increasing availability of information technology and communications. This embodies a framework potentially injurious for health and quality of life. The resulting modern style is the increase in non-communicable chronic diseases and the continuing deterioration of nutritional status and health; this is observed in all socioeconomic levels and all along the life cycle. Prevention is the only possible approach to the control of the double burden of malnutrition and lack of physical activity, which together impose a high cost to health systems, especially in poor and / or underdeveloped countries.
The low demand for physical activity of modern lifestyle accelerates deterioration of human capabilities and body composition (BC) changes. This is mainly due to two convergent situations: decreased daily energy expenditure and on the other hand, muscle is lost either not adequately developed and fat deposits are increased. Both of them form a negative cycle that eventually affects health and full development. One of the most obvious manifestations of this process is the increase in body weight. Today we know that body weight is a very nonspecific indicator in relation to health, instead, the BC, defined as the number and proportion of each component of the total body mass, is better related to the risk of developing non-.communicable chronic diseases (NCDs). Therefore, the knowledge of the BC has significant value in health, physical improvement and human performance. BC assessment requires the availability of tools, which would be able to predict accurately, each one of the body components. In this case, the fat mass (FM) component is relevant to be linked directly to the development of chronic diseases.
In Argentina, as in most Western countries, people is suffering from a severe epidemic of NCDs especially cardiovascular often stems from obesity. Obesity is a disease characterized by increased FM, as defined by the WHO in 1995. In most cases, it is accompanied by increase of body weight, though not always. Consequently, it is necessary to have reliable, accurate and simple methods to measure and / or diagnose FM status.
The lack of validated methods in Argentina.
In Argentina, as well as in many Central and South American countries, there are not previous studies that develop tools for measuring the BC in children. The methods and equations that we have been applying at present were developed in geographic, cultural and ethnical different world regions of Argentina. So, the lack of appropriate tools limits the suitable evaluation of health programs and clinical and/or sportive practices. This raises the need for developing own methodological resources, according to local characteristics, which would be validated with ¿gold standard¿ methods.
It was our purpose to contribute to improving the tools for evaluating prevention and health promotion programmes by developing low-cost tools for easy application and evaluation of BC, while attempts to confirm the relationship between aerobic performance and BC school children.
General aim.
To develop valid predictive equations for the estimation of body composition of children by anthropometry and bioelectrical impedance.
Specific aims.
1. To assess body composition of children by anthropometric measurements, bioelectrical impedance, and deuterium dilution technique.
2. To compare equations available in the literature for the FFM or the FM.
3. To develop body composition estimation equations for Argentinean children using anthropometry and bioelectrical impedance.
4. To validate the new equations obtained using the reference method of isotope dilution technique with deuterium.
5. To explore the association between aerobic component of fitness and fat mass.
Methods.
Study Design and sample. The study was based on a non-experimental, descriptive, cross-sectional and correlation design. The sample obtained was 152 children, 80 (52%) girls and 72 (48%) boys, between 6 to 9 years old.
Anthropometry. Body weight (BW, kg) and height (H, m) were measured, and the Body Mass Index (BMI) was calculated as BMI equal to BW over squared H (kg/m2). Skinfolds (triceps, biceps, subscapular and abdominal) were also measured with a Lange calliper (mm) and waist circumference with an anthropometric tape (cm).
Bioelectrical impedance. It was used a dual-frequency bioelectrical impedance (Bodystat Co Dual Scan 2500) to measure the resistance in ohms and calculate the resistance index (RI) as resistance/ H2 (Ohms/cm2). This device conducts an electric current of 5 to 200 kHz, which offer a suitable way to estimate total body water, intracellular water, extracellular water and fat free mass.
Total body water by deuterium isotope dilution. To estimate the fat-free mass (FFM) and fat mass (FM), it was determined the total body water (TBW) by the isotope dilution method with deuterium oxide or deuterated water. This method is based on the dilution principle by which it is possible to know the subject TBW under study from the administration of a known dose volume (V1) and concentration (C1) of deuterated water and the determination of the concentration deuterium (C2) in a sample of saliva, afterwards we can know the total volume where deuterium was diluted (V2). For this, saliva samples were collected in order to determine the children deuterium baseline. The subjects received an oral dose of 0.5 g deuterium oxide / kg body weight (99.8%, Cambridge Isotope Laboratories, Boston, USA). After equilibrium was reached, in approximately 3 hours, a saliva sample was collected. The deuterium concentration in saliva (C2) was measured on a mass spectrophotometer. Total body water (TBW) was calculated as V1*C1 / C2, and the FFM was calculated according FFM= [(TBW /HC) / 1.04], where HC is the coefficient of hydration of FFM in a range of 74.9 to 77.0 for both sexes, and 1.04 is a correction factor of the hydrogen exchange. The percentage of body fat was calculated by the model %FM = (BW - FFM) / BW * 100. Children were granted to participate in this study.
Measurement of aerobic performance. Each child performed a 6-minute walking test (6MWT). The test consisted in walking 6 minutes continuously in order to cover the greatest possible of meters. The children might slow down if needed and, if they stopped, we measured walking distance as fast as possible. The test is stopped if the child has any signs or symptoms of excessive fatigue or other inappropriate response to stress. There were recorded heart rate (HR) at initial, intra effort and resting at 30, 60 and 90 seconds.
Statistical analysis. The variables are shown as means and standard deviation. It was performed a description of variables and applied the Shapiro Wilk test to verify the null hypothesis that the variances are normally distributed. To define which variables enter the model, it was applied the Mallows criteria (Cp), where the best combination is one that gets a Cp equal to the number of variables plus one (n + 1). It was used the method of all possible regressions to develop each prediction equation. Bland and Altman analysis was performed to verify the agreement between fat masses estimated by the new anthropometric model and the classical reference standard from total body water by isotope dilution technique; the same procedure was also performed for fat-free mass by bioelectrical impedance (BIA). In addition, it was also calculated the Lin agreement correlation coefficient of the regression (rc) of the estimated fat mass from prediction models relative to fat mass determined by deuterium isotope dilution as the reference method.
Results.
Sample characteristics on average were 7.5±1.02 years, BW 27.79 ±5.85 kg, H 125.44± 7.25 cm, BMI 17.53±2.44 kg/m2.
Nutritional status was assessed using BMI as reference so 8 girls (10%) and 4 boys (5.55%) were obese; also, overweight was observed on 22 girls (27.50%) and 19 boys (26.38%). There were not significant statistically differences between sexes regarding number of cases for BMI levels. The prevalence of overweight and obesity were slightly lower than the national average reported by the last National Nutrition and Health Survey (ENNYS 2010), which stated that the sample was not far from the national average.
Total body water, fat mass and fat-free mass of deuterium isotope dilution for both sexes were: TBW (L) 14.87±2.40, TBW (%) 54.76 ±4.78, FFM (kg) 19.48±3.27, FFM (%)71.65±6.42, FM (kg) 8.0±3.26, FM (%)28.35± 6.42. It was observed significant difference between sexes in TBW (%), FFM (%) and FM (%) (p<0.001). The RI was 23.58±3.51 (R/H2).
Development fat-free mass prediction equations by bioelectrical impedance.
The steps followed to obtain the prediction equations or models using BIA variables body weight (BW), resistance index (RI) and height (H), were:
Step 1: control of outliers. Twelve subjects were dropped out of the analysis. Errors in the determination of deuterium in the saliva were the cause to take out them of database.
Step 2: Randomization of the sample using Excel randomization function.
Step 3: Control of variables outliers.
Step 4: sample division. The sample was randomly split into two equal groups. One to obtain the model (base A) and, the second as validation group (base B).
Paso 5: Association analysis between FFM and variables BIA.
Paso 6: Description of the model.
BIA model.
Bivariate model to predict FFM from RI and Height.
FFM (kg) = -12.3361 + 0.4572 (RI) + 0.1637 (Height) Model characteristics: R2= 0.8916 S=0.9710 Cross validation.
Regression analysis between estimated values from our new equation and measured by deuterium dilution showed slope (b) = 1.0293, intercept = -0.1691, r = 0.871, R2 = 0.759, (P<0.001). The next step in the validation was to calculate the concordance correlation rc = 1.021, confirming the reproducibility. Finally it was evaluated the agreement between methods by using the Bland and Altman analysis, and did not show any bias.
Development of body fat prediction equations by anthropometry.
Similar to BIA model steps were followed to develop the FM anthropometric model. However, it was obtained three valid models.
Anthropometric Models.
Bivariate model to estimate FM based on weight and the sum of four skinfolds.
FM (kg) = -3.2120 + 0.2829 (weight) + 0.0796 (Sum of 4 skinfolds) Model characteristics: R2= 0.9143 S=0.7388.
Cross Validation.
Regression analysis between estimated values from the first FM equation and those measured by deuterium dilution showed slope (b) = 0.807 and intercept = 1.158, r = 0.872, R2 = 0.760 (P<0.001). The intercept value implies a systematic deviation of 1.2 kg of the new model. The concordance correlation of the equation obtained was 0.786, meaning that the validation of the first model was correct and its reproducibility was acceptable. Bland and Altman plot did not show any proportional or systematic bias.
Bivariate model to estimate FM based on weight and triceps skinfold.
FM (kg) = -4.7343 + 0.3148 (Body Weight) + 0.3029 (Triceps skinfold) Model characteristics: R2= 0.8389 S=1.0332.
Cross Validation.
Regression analysis between estimated values from the second FM equation and those measured by deuterium dilution showed slope (b) = 0.783, intercept value = 1.516, r = 0.783, R2 = 0.613 (P<0.001), While r, R2 and b are suitable, the intercept value was moderately high, implying a deviation close to 1.5 kg from 0 values. The concordance correlation (rc) of the obtained equation was 0.782, which means that the reproducibility of the second model was high because not significantly different from 1. Bland and Altman plot confirmed agreement between models.
Bivariate model to predict FM based on weight and waist circumference.
MG (kg) = -7.8366 + 0.3942 (Body Weight) + 0.0856 (Waist Circumference) Model characteristics: R2= 0.7553 S=1.1554 Cross validation.
The final regression analysis to validate the third model showed r = 0.776; R2 = 0.602; (P<0.001), so the coefficients were far from the perfect value of 1 for slope (b = 0.7345) and 0 value for intercept (intercept = 1.766) and, although both were significantly valid, they should introduce large errors for FM estimations (close to 1.8 kg). The concordance correlation (rc) of the obtained equation was 0.777, confirming reproducibility, as not significantly different from 1. Bland and Altman analysis did not show any bias.
Aerobic test performance of 6 minutes and its relation to fat mass The walked distance was 566.7±50.0 (m), did not exits significant difference between sexes (P<0.07). FM had a significant relationship with the HR90¿ in boys.
Conclusions.
¿ The measurement of TBW with isotope dilution method with deuterium had been successfully implemented for the first time in Argentina, which will facilitate its use as a standard reference in future BC studies in our country.
¿ The children BC data evaluated by deuterium isotope dilution method were 28.35 ±6.42% of body fat and TBW accounts for 54.76 ± 4.78%. There were significant differences between sexes for both components. Boys had more FFM and larger percentage of water than girls.
¿ The equations available in the literature, which are more often used in Argentina for predicting BC of children from 6-9 years, either through BIA and anthropometry, are imprecise or have shown large variations among them.
¿ Using TBW by isotope dilution with deuterium as a standard reference, we obtained and validated the following equation to estimate FFM by BIA: FFM (kg) = -12.3361 + 0.4572 (RI) + 0.1637 (Height). Its deviation from the reference was 170 g, which was close to an ideal model.
¿ It have been also obtained and validated, the next equations to estimate FM with anthropometric variables:
¿ FM (kg) = -3.2120 + 0.2829 (weight) + 0.0796 (sum of biceps, triceps, subscapular and abdominal skinfolds).
¿ FM (kg) = -4.7343 + 0.3148 (weight) + 0.3029 (triceps skinfold).
¿ FM (kg) = -7.8366 + 0.3942 (weight) + 0.0856 (waist circumference).
¿ The application for the first time in schoolchildren from Argentine, aged between 6 and 9 years, the 6MWT has confirmed to be simple and safe, so it can be used as a tool to assess submaximal aerobic capacity or cardiorespiratory fitness.
¿ None differences were found in the distance that was performed in the 6MWT, among sex, BMI or FM categories. The recovery heart rate in boys was positively associated with FM and FFM, which means that higher FM is related greater internal load (cardiovascular stress) for children exercising with the same external load.
