the data were collected as part of nationwide screening programs in 3 consecutive years in 2007 , 2008 and 2009 . this program is regularly performed by the ministry of health and medical education and the ministry of education and training among all children entering elementary schools . elementary education is mandatory in iran , thus the study population comprised all children entering public and private elementary schools . the national data and safety monitoring board closely supervised the quality control and quality assurance of each survey . training sessions were organized for health care providers who measured children 's weight and height according to standard protocols by using calibrated instruments.15 body mass index ( bmi ) was computed as weight in kilograms divided by the square of height in meters . in all surveys , we used the growth charts of the centers for disease control and prevention,16 which are in close agreement with iranian charts.17 overweight and obesity were considered as age- and gender specific bmi of 85 - 94 and  95 percentile curves , respectively.16 because of significant differences in the prevalence of overweight and obesity among adults in the northern , central and southern regions of iran , with similarities in the geographic and socio - demographic characteristics in each region,18 in this study we compared the corresponding figures for children . after editing , the data were analyzed using the statistical package for social sciences statistical software package version 16:0 ( spss inc . , all analyses were initially stratified by gender , but as the differences were not significant , the results are presented for girls and boys in combination . data were obtained from all 6-year - old children entering elementary schools in all 30 provinces in iran . the study population comprised 2,600,065 children including 862,433 in 2007 , 782,244 in 2008 and 955,388 in 2009 . of total children , 12.8% , 13.5% and 10.9% were overweight in 2007 , 2008 and 2009 , respectively ( p > 0.05 ) . the corresponding figures for obesity were 3.4% , 3.5% and 3.4% , respectively ( p > 0.05 ) . figure 1 presents the prevalence and trend of overweight and obesity in the three regions of the country . in all surveys , the prevalence of overweight was higher in southern region than in the other two regions . p for trend was not significant for prevalence rates of overweight and obesity in none of the regions . secular trends in prevalence of overweight and obesity in 6-year - old iranian children during 2007 - 2009 in a. northern , b. central and c. southern regions . this study , presenting the national trend of about 2,600,000 children over three years revealed no significant difference of prevalence of overweight and obesity over a 3-year period ( 2007 - 2009 ) . various health policies have been implemented to improve the nutritional status of iranian children from early life . the focus of most of them has been to control underweight and micronutrient deficiency . as recent national studies showed considerably high prevalence of overweight and obesity in iranian adults1819 and school - aged children,20 in addition to the aforementioned policies , primordial and primary prevention of childhood overweight have been considered in the program of health professionals , notably pediatricians , general physicians and child health care providers . moreover , in order to increase the public awareness about the importance of prevention and control of overweight in children , mass media programs were used as a tool to advocate for children 's healthy lifestyle and more specifically preventing child overweight . given that small changes at the individual level may result in large benefits at the population level , such policies might have been effective , so that the childhood overweight and obesity rates have remained constant for at least three years . however , as some regional studies revealed increasing trend of overweight and obesity in adults21 and school - aged children,22 more intensive interventions and legislations are necessary to tackle obesity in older ages . at a very young age , children 's lifestyle is more under control of parents and they can guide their children in making choices that will lead to healthier lives . by getting older , children may feel they have more power over their choice of foods and activity , and may adopt obesogenic lifestyle behaviors . it is noteworthy to mention that in all three surveys , children living in the southern region had the highest prevalence of overweight . this higher prevalence might be because of differences in socioeconomic background of this region , as well as ethnic differences . in general , the southern provinces in iran have lower socioeconomic position than other provinces . some studies in developing countries reported higher rates of childhood obesity in higher socioeconomic populations,12 whereas others reported it in lower socioeconomic class.2325 an increasing body of evidence showed that over the past years , a secular trend toward increase in obesity is more marked among children of lower than higher socioeconomic status , which might be because low - income households can affect a child 's tendency to gain weight by higher intake of energy - dense foods , lower intake of complex carbohydrate , fruits and vegetables.2629 moreover , regarding the ethnic differences in the prevalence and complications of childhood obesity,3031 and considering the popularity of arab ethnicity in southern iran , part of this difference might be explained by ethnicity . future studies about lifestyle behaviors in this region might help to design more effective preventive and interventional programs . in other viewpoint , although there was no significant increase in the prevalence of overweight and obesity in children at school entry , but in general , the prevalence of overweight is high at a level comparable to developed countries . because of the very large sample size of the study in 3 consecutive years , details on socio - economic background and lifestyle habits of the children under study could not be documented . the main strengths of the study are its novelty in reporting national trends of childhood overweight from a developing country , and the nationwide coverage of all schoolentry children . because of the very large sample size of the study in 3 consecutive years , details on socio - economic background and lifestyle habits of the children under study could not be documented . the main strengths of the study are its novelty in reporting national trends of childhood overweight from a developing country , and the nationwide coverage of all schoolentry children . because of the very large sample size of the study in 3 consecutive years , details on socio - economic background and lifestyle habits of the children under study could not be documented . the main strengths of the study are its novelty in reporting national trends of childhood overweight from a developing country , and the nationwide coverage of all schoolentry children . to the best of our knowledge , this study is the first of its kind in reporting the nationwide trend of overweight and obesity among young children living in a developing country . it revealed a considerably high prevalence of overweight and obesity among young iranian children , but with a constant rate in three years . the higher prevalence of overweight in southern region than in central and northern regions in all three surveys might be related to the lower socioeconomic position of this region . at a very young age , children 's lifestyle is more under control of parents and they can guide their children in making choices that will lead to healthier lives , primordial and primary prevention efforts against the overweight epidemic can be effective and shall be further strengthened .