controlling overweight and obesity in adolescence is a challenge for physicians and nutritionists . eating habits in this age group are characterized by a preference for fast foods with a high fat and carbohydrate composition , with an increased rate of calories and low nutritional value . the food preferences of adolescents can lead to obesity and overweight when combined with a sedentary lifestyle represented by long time periods dispensed to low - intensity physical activities , such as watching television and using the computer . therefore , responsible nutritional habits should also be incorporated in official guidelines for school nutrition . , the nutritionist or pediatrician makes a diagnosis if growth is moving away from the standard expected of disease and/or unfavorable social conditions . the main objective of the nutritional assessment is to determine the growth and body proportions in an individual or community . as a consequence , earlier interventions may be imposed by improving the quality of life of the population in general . there is no way to reduce malnutrition and obesity if they are not diagnosed correctly . body mass index ( bmi ) or quetelet index has been established as an important diagnostic method for nutritional profile assessment in several populations . the importance of bmi has been recognized by the world health organization ( who ) . what is already known about this topic ? first , childhood obesity is difficult to conceptualize ; and second , there is not an international consensus on the best anthropometric criteria to be used for the evaluation of overweight and obesity in adolescents . therefore , this study aimed to evaluate the prevalence rate of underweight , overweight , and obesity among brazilian school adolescents using the cut - off points for bmi according to brazilian reference during the period between january 2014 and december 2014 . to prevent errors in this epidemiologic study , we applied the methodological criteria recommended by the strengthening the reporting of observational studies in epidemiology guidelines . this epidemiological design was an observational , descriptive , cross - sectional and population - based study with a cohort of school adolescents . the sample consisted of 2162 school adolescents enrolled in all 20 government schools during the period from january 2014 to december 2014 . assessment of anthropometric measurements body weight and height were assessed by nutritionists in schools , according to rules established by the brazilian institute of geography and statistics manual . students were placed against the wall , barefoot , with the heels touching the wall , and the value was recorded in centimeters with one decimal place . body weight was measured using a portable scale , with resolution up to 500 g. the students wore light clothes and were barefoot . the value was reported in kilograms to one decimal place , and bmi was calculated as the ratio between body weight ( kilograms ) and the square of height ( m ) . in this research , as reference values for bmi in brazilian adolescents , we used the cut - off point recommended by conde and monteiro for anthropometric measurements in the brazilian population . the age limits of adolescence are 10 years old and 19 years old according to the who . the exclusion criteria included some conditions present in the medical reports of adolescents , such as thyroid , renal , and liver diseases , use of oral corticosteroids , anabolic steroids , and beta - blockers . other exclusion criteria were adolescents who refused to participate in the study , student younger than 10 years and older than 19 years , pregnancy , and adolescents with special needs . the cut - off points for bmi according to conde and monteiro ( brazilian criteria ) for students of both sexes between 10 years old and 19 years old were as follows : underweight ( bmi 17.5 kg / m ) , overweight ( bmi 25.0 kg / m ) , and obesity ( bmi  30.0 kg / m ) . we defined period prevalence as the number of school adolescents with underweight , overweight , and obesity , divided by the total number of school adolescents in the sample . the anthropometric evaluations were entered into microsoft office excel 2010 and exported from the database to the following software programs : graphpad prism , version 2015 ( graphpad software , inc . san diego , california , usa ) ; ncss10 software , version 2015 ( ncss , llc , kaysville , utah , usa ) ; who anthroplus software , version 3.2.2 ( freely distributed and copied by who , geneva , switzerland ) to determine bmi ; and epitools epidemiological calculators , ( copyright 2015 by ausvet animal health services ) . the following statistical tests were performed : ( 1 ) central limit theorem , in which very large sample size had a normal distribution . ( 3 ) student 's t - test was used with the aim of comparing differences in the arithmetic means of the normally distributed continuous variables . ( 4 ) the z - test was used to compare proportions for categorical variables . ( 5 ) the chi - square test with a trend line was used for associations among obesity and age in a contingency table , with two columns and ten rows for both sexes . ( 6 ) p < 0.05 ( two - tailed ) was considered to be statistically significant and sufficient enough to reject the null hypothesis and define a type i error . this epidemiological design was an observational , descriptive , cross - sectional and population - based study with a cohort of school adolescents . the sample consisted of 2162 school adolescents enrolled in all 20 government schools during the period from january 2014 to december 2014 . assessment of anthropometric measurements body weight and height were assessed by nutritionists in schools , according to rules established by the brazilian institute of geography and statistics manual . students were placed against the wall , barefoot , with the heels touching the wall , and the value was recorded in centimeters with one decimal place . body weight was measured using a portable scale , with resolution up to 500 g. the students wore light clothes and were barefoot . the value was reported in kilograms to one decimal place , and bmi was calculated as the ratio between body weight ( kilograms ) and the square of height ( m ) . in this research , as reference values for bmi in brazilian adolescents , we used the cut - off point recommended by conde and monteiro for anthropometric measurements in the brazilian population . the age limits of adolescence are 10 years old and 19 years old according to the who . the exclusion criteria included some conditions present in the medical reports of adolescents , such as thyroid , renal , and liver diseases , use of oral corticosteroids , anabolic steroids , and beta - blockers . other exclusion criteria were adolescents who refused to participate in the study , student younger than 10 years and older than 19 years , pregnancy , and adolescents with special needs . the cut - off points for bmi according to conde and monteiro ( brazilian criteria ) for students of both sexes between 10 years old and 19 years old were as follows : underweight ( bmi 17.5 kg / m ) , overweight ( bmi 25.0 kg / m ) , and obesity ( bmi  30.0 kg / m ) . we defined period prevalence as the number of school adolescents with underweight , overweight , and obesity , divided by the total number of school adolescents in the sample . the anthropometric evaluations were entered into microsoft office excel 2010 and exported from the database to the following software programs : graphpad prism , version 2015 ( graphpad software , inc . san diego , california , usa ) ; ncss10 software , version 2015 ( ncss , llc , kaysville , utah , usa ) ; who anthroplus software , version 3.2.2 ( freely distributed and copied by who , geneva , switzerland ) to determine bmi ; and epitools epidemiological calculators , ( copyright 2015 by ausvet animal health services ) . the following statistical tests were performed : ( 1 ) central limit theorem , in which very large sample size had a normal distribution . ( 3 ) student 's t - test was used with the aim of comparing differences in the arithmetic means of the normally distributed continuous variables . ( 4 ) the z - test was used to compare proportions for categorical variables . ( 5 ) the chi - square test with a trend line was used for associations among obesity and age in a contingency table , with two columns and ten rows for both sexes . ( 6 ) p < 0.05 ( two - tailed ) was considered to be statistically significant and sufficient enough to reject the null hypothesis and define a type i error . the number of students included in the analysis was 2162 , of which 1527 were males ( 71.0% ) and 635 were females ( 29.0% ) , with a z = 18.0 ( p = 0.00001 ) . the arithmetic mean of age ( in years ) was 13.14  2.17 for males and 12.66  1.85 for females , with an unpaired t - test equal to 4.74 ( p = 0.0001 ) . the coefficient of variation ( cv ) for the age of the students was 16.52% and 14.65% , respectively . the anthropometric characteristics of all school adolescents of both sexes are shown in table 1 . the height ( cm ) , body mass ( kg ) , and bmi ( kg / m ) for males were 1.60  0.14 , 52.0  15.0 , and 20.0  4.0 , respectively . the height ( cm ) , body mass ( kg ) , and bmi ( kg / m ) for females were 1.50  0.09 , 50.0  13.0 , and 21.0  4.6 , respectively . when both sexes were compared for height , body mass , and bmi , the t values , were 7.57 ( p = 0.0001 ) , 2.47 ( p = 0.0136 ) , and 3.82 ( p = 0.0001 ) , respectively . the cv was higher than 20% for only bmi in males and females , with values between 20.02% and 22.36% , respectively . anthropometric characteristics of all school adolescents of both sexes ( n=2162 ) table 2 shows a comparison of the bmi of underweight , overweight , and obesity in brazilian school adolescents . according to student 's t - test , there was not a statistically significant difference between the arithmetic means in both sexes for underweight ( p = 1.00 ) and obesity ( p = 0.089 ) . however , the comparison of overweight for both sexes was statistically significant ( p = 0.044 ) . body mass index of underweight , overweight , and obesity in brazilian school adolescents of both sexes table 3 shows the prevalence of nutritional status among the population studied using a brazilian reference for adolescents . there was no statistically significant difference in both sexes for overweight ( z = 0.60 , p = 0.5469 ) and obesity ( z = 0.30 , p = 0.7863 ) . however , the comparison of underweight for both sexes was statistically significant ( z = 7.80 , p = 0.001 ) . prevalence of nutritional status in brazilian school adolescents in both sexes figure 1 shows a histogram representing the prevalence rate distribution and association with obesity and age of the school adolescents ( n = 60 ) . the trend line shows an inverse relationship between obesity and age among the school adolescents of both sexes . the association with a chi - square test for a linear trend was 30.95 ( p = 0.01 ) . histogram representing the prevalence distribution and association of obesity and age of the school adolescents ( n = 60 ) . the trend line shows an inverse relationship between obesity and age among the school adolescents for both sexes . adolescence can be considered a transitional stage from puberty to adulthood . however , adolescence has stages of development according to different ages within this age range . many authors have described such physical , intellectual , emotional , and social development . considering these different stages , the who mentioned many causes of illness and disability among adolescents , such as asthma and lower respiratory infections , use of alcohol , hiv / aids , anxiety , and depression , among others . endocrine disorders were among ten top causes of death in adolescents in 2012 . in high complexity centers for diagnosis , thus , the main cause of obesity in adolescents and other children is exogenous factors or increased caloric intake and decreased physical activity . it is associated with a variety of risk factors for type 2 diabetes , insulin resistance , metabolic syndrome , dyslipidemia , systemic arterial hypertension , and atherosclerosis . there is consensus that bmi should be used in the collective assessment and perhaps individual for assessment of nutritional status in adolescents . the height and body mass for both the sexes among school adolescents in our study [ table 1 ] was in accordance with data from brazilian institute of geography and statistics . in a government report from 2008 to 2009 , the median range of height among brazilian adolescents was 1.391.72 m for males and 1.4 m to 1.61 for females . the median of body mass was reported with a range of 33.465.9 kg in males and a range of 34.356.2 kg for females . the conde and monteiro criteria for the diagnosis of nutritional status by bmi in adolescents are shown in table 2 . however , these authors also agree that the adoption of the proposed cut - off point for underweight requires further analysis and discussion . however , the method used in brazilian references was basically the same as that used in the calculation of the value of the international bmi standard . in this study , the prevalence rates of underweight , overweight , and obesity observed in our population of school adolescents according to the brazilian bmi criteria were 2.8% , 8.1% , and 2.4% for males , respectively , and 23% , 10.7% , and 3.6% for females , respectively [ table 3 ] . the prevalence rates for both sexes were similar to those of other studies that used the conde and monteiro criteria . different from our results and those of other researchers , the prevalence of overweight and obesity was 14% and 23% , respectively , among girls in a district school in bangladesh . the prevalence rate of excess weight ( overweight and obesity ) in our school adolescents was 10.5% for boys and 14.3% for girls . . found similar results with the national criteria in a sample of 3118 school adolescents in the northern region of brazil , i.e. , 11.6% and 14.6% prevalence of excess weight for boys and girls , respectively . flores et al . showed a prevalence rate of 27.6% for boys and 33.8% for girls . our results in figure 1 show a statistically significant inverse association between obesity prevalence and age in school adolescents . the choice of the brazilian reference for the calculation of prevalence rates of anthropometric status in adolescents can be compared to other international criteria . international references for comparisons of the prevalence rate are 518% for overweight and 0.14% for obesity at 218 years old . the results of our study are in the international reference range as shown in table 3 . however , the prevalence rate of underweight in our population was very high among girls ( 23.0% ) compared to boys ( 2.8% ) and was statistically significant ( p = 0.001 ) , as shown in table 3 . an international study of the trends of obesity and underweight in many countries showed that the prevalence rate of underweight was 6.5% among girls in 1997 in brazil . in 12 schools of bhubaneswar , state of odisha , india , the prevalence of overweight and obesity among adolescents in private schools was significantly higher ( 45.2% ) than those in government schools ( 10.5% ) . what are the implications ? we recommend bmi as the best procedure for monitoring and diagnosing obesity in health campaigns . this study concludes that the occurrence of excess weight among our school adolescents was similar to the international prevalence . however , the prevalence rate of underweight in our population was very high among girls ( 23.0% ) . the results of the diagnosis of nutritional status of every adolescent were sent with knowledge of the parents . the current study can not be extrapolated to the entire population of brazilian adolescent students because this research was conducted with a specific population group . the nutritional status of adolescents must be considered to be a public health problem in brazil .
introduction : the nutritional profile of the brazilian population has changed in recent years . therefore , this study aimed to assess the prevalence of nutritional status among brazilian school adolescents during the period from january 2014 to december 2014.methods:this study employed an observational design with a cohort of school adolescents . 
 anthropometric measurement was assessed by nutritionists in government schools . 
 the cut - off points for body mass index according to brazilian criteria for adolescents of both sexes between 10 years and 19 years old were underweight ( 17.5 kg / m2 ) , overweigh ( 25.0 kg / m2 ) , and obesity ( 30.0 kg / m2).results : the number of students included in the analysis was 2162 , of which 71.0% were males and 29% were females ( p = 0.00001 ) . 
 the mean age ( years ) was 13.14  2.17 for boys and 12.66  1.85 for girls ( p = 0.0001 ) . 
 the prevalence of underweight , overweight , and obesity observed in our population of school adolescents according to the brazilian criteria was 2.8% , 8.1% , and 2.4% for males , respectively , and 23.0% , 10.7% , and 3.6% for females , respectively . for both sexes 
 , there was no statistically significant difference between overweight ( p = 0.5469 ) and obesity ( p = 0.7863 ) , but there was for underweight ( p = 0.001).conclusions : the occurrence of excess weight among brazilian school adolescents is similar to the international prevalence , but the prevalence of underweight was very high among girls . the nutritional status of adolescents must be considered a public health problem in brazil .