Anthropometric studies in children and adolescents are important; since they enable us to screen changes in growth and puberty. In addition, given growth may be affected by nutritional disorders, adolescents anthropometric also reflects nutritional status and health risks (Sodaei et al., 2013). In this regard, the most common index used to assess weight disorders, including underweight, overweight, and obesity, is the body mass index (BMI), which is obtained by dividing weight in kilograms by height squared in meters (Güngör, 2014, Kumar and Kelly, 2017).
Statistics from previous literature have shown that world has witnessed over the past three decades a shift from the high prevalence of underweight to the high prevalence of overweight and obesity in low and middle-income countries (Bentham et al., 2017, Greydanus et al., 2018).The decline in the prevalence of underweight compared to overweight and obesity may be due to urbanization, industrialization, lifestyle changes, food security, and health education (Heidari-Beni and Kelishadi, 2019, Weihrauch-Blüher and Wiegand, 2018). Evidence from the data have shown a significant increase in the prevalence of obesity in each country from 1975 to 2016 (Greydanus et al., 2018). In fact, overweight and obesity has been mentioned as one of the most important health challenges of the 21^st century (World Health Organization, 2018).
Obesity is indeed a multi factorial disease in which genetic and environmental factors, such as physiological, biochemical, metabolic, psychological, and social factors are involved (Khazaei et al., 2017a, Sanyaolu et al., 2019). Increased intake of high-calorie foods, decreased physical activity, and increased sitting activities are the main factors associated with increasing the prevalence of obesity in children and adolescents (Sahoo et al., 2015). On the other hand, it should be noted that children are significantly more likely to be malnourished due to their special nutritional needs for growth (gholami et al., 2014). Underweight also has very negative effects on quality of life and health status. It can be said that obesity it is an important problem , especially in growing children (Heidari-Beni and Kelishadi, 2019).
Many studies have shown that childhood obesity and its associated metabolic effects are transmitted to adulthood (Simmonds et al., 2016) Therefore, identification of children who are at high risk for obesity, reduce the risk of obesity in adulthood if combined with weight loss and improved lifestyle.
Based on epidemiological evidence, obesity in childhood and adolescence increases the risk of some diseases, such as metabolic syndrome (MetS), cardiovascular disease (CVD), hypertension (HTN), type-2 diabetes mellitus (T2DM), dyslipidemia (DL), and arteriosclerosis in adulthood. It also increases the risk of CVD in childhood and adolescence (Weihrauch-Blüher et al., 2019).
Considering the role of childhood and adolescence obesity in adulthood, the consequences of obesity on the growth and development of children in the following years of life, the heavy burden of this disorder for health care systems, as well as having an insight on the prevalence and trend of childhood and adolescents underweight, overweight, and obesity can
provide evidence-based information for health policymakers at national levels in order to plan and implement programs for primary prevention.
Despite previously mentioned evidence which has examined the prevalence of obesity or malnutrition in children and adolescents in different cities of Iran, no study has yet indicated the prevalence of weight disorders in urban and rural areas of Lorestan province. Also, most studies have reported results based on one criterion. However, the present study considered three different criteria for estimating the prevalence. Therefore, this cross sectional study was designed to investigate the prevalence of weight disorders in children and adolescents in Lorestan province based on different cutoffs related to the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), and National Growth Charts for BMI among Iranian children and adolescents to assist policy-makers in developing preventive strategies and guide further research.
Materials and Methods
Study design and participants: This population-based cross-sectional study was done on 30532 children and adolescents aged 6-18 years in the framework of the national survey of Iranian children and adolescents' psychiatric disorders (IRCAP project) in all provinces of Iran using a multistage cluster sampling method.
This project was designed by the Department of Nutrition and Psychiatry and performed by the Psychiatric Research Center of Tehran University of Medical Sciences and funded by the National Institute for the Development of Medical Research (NIMAD).
In this study, children and adolescents aged 6-18 years were selected by multi-stage cluster sampling (cluster sampling and random classification) from urban and rural areas of Lorestan province. Based on the sampling method, 150 clusters of houses were randomly selected based on postal codes in both rural and urban areas. In each cluster, 6 children and adolescents were randomly selected within equal blocks of gender and age groups (6-9 years, 10-14 years, and 15-18 years). If the selected family did not have a child in the age range of 6-18 or no one was at home, the next license plate was referred. The clusters were selected randomly according to the postal code received from the post office. All Iranian citizens aged 6-18 years who resided in Lorestan province for at least one year were eligible to participate in this study. The exclusion criterion included non-Iranian citizens and immigrants. Furthermore, those who did not consent to participate were excluded.
Finally, a total of 866 children and adolescents living in urban and rural areas of Lorestan province were evaluated for BMI and entered the epidemiological and analysis stage.
Measurements: Sociodemographic information was collected by a questionnaire developed particularly for this study. Demographic and familial characteristics included gender, age, residential area, parental education levels, parental job, and a history of parental physical or mental illness, the data about which were gathered via self-report using a semi-structured questionnaire. Moreover, accurate measurements of anthropometric indices were collected by the researchers. More detailed information about the study design, participants, and data collection method have been published previously (Mohammadi et al., 2019).
Data collection was done by 6 trained interviewers referring to houses and explained the study process to the interviewees. Parents were invited to take part their children in the study and then written consent form was received from parents and adolescents.
In addition to the main questions of the IRCAP study, the interviewers also collected demographic and anthropometric data, including accurate measurements of height and weight of children and adolescents. BMI was then calculated using the weight (kg)/height (m)² formula.
In the age group of children and adolescents, gender-specific BMI-for-age percentile curves were used to define abnormalities in BMI. Hence, standard percentiles and cutoffs were set by WHO and CDC. Based on these percentages, children and adolescents were classified into different groups, including underweight, normal weight, overweight, and obese. Standard percentages of BMI also depend on other factors, such as genetics (ethnicity), environmental, and demographic-social factors (Albrecht and Gordon-Larsen, 2013, Veghari, 2012). Therefore, national percentiles determined in previous studies in Iran are of great importance.
Ethical considerations: Written consent was obtained from parents of participants aged less than 15 years and from the participants and their parents of adolescents aged 15-18 years. All information about the participants and their families were kept confidential. The Ethics Committee Board of the National Institute for Medical Research Development (NIMAD) approved this study (the ethics code: IR.NIMAD.REC.1395.001).
Data analysis: The collected data were analyzed using SPSS software version 19 (IBM SPSS Statistics for Windows version 19.0, Armonk, NY: IBM Corp) and Chi-square test was used to compare the genders and age groups. In this study, BMI classification was performed according to National Growth Charts for BMI among Iranian children and adolescents in comparison with the WHO and CDC curves as follows (Mohammadi et al., 2020).
Underweight: BMI less than the 5^th percentile of the country.
Normal weight: 5^th to 85^th percentile of the country.
Overweight: 85^th percentile to less than 95^th percentile of the country.
Obesity: more than 95^th percentile of the country.
Therefore, the prevalence of underweight, overweight, and obesity were reported and compared using the cut point of Iran, WHO, and CDC.
Results
Study population characteristics: A total of 866 children and adolescents aged 6-18 years took part in the study, 447(51.6%) of whom were girls and 419 (48.4%) were boys. Moreover, 75.8% of the participants lived in urban areas and others (24.2%) lived in rural areas. Table 1 shows that the total prevalence of overweight and obesity among boys was 17%, while was 12.5 % among girls. The prevalence of underweight in girls was 5.8% (n=26), while it was 4.5% (n=19) in boys. Finally, the results indicated that among three considered status (underweight, overweight, and obesity), the highest rate is primarily related to overweight with a prevalence of 9.7%, then underweight 5.2%, and finally obesity with a prevalence of 5%. There were no significant differences in the prevalence of underweight, overweight, and obesity between urban and rural areas.
Comparison of BMI percentile: Table 2 shows BMI of Iranian children and adolescent percentiles in comparison to CDC and WHO reference data. It shows that the prevalence of underweight, overweight, and obesity according to the WHO criteria are 12%, 13%, and 9.2%, respectively, and based on the CDC reference the prevalence are12.6%, 15.8%, and 4.2%; however, both of these statistics are very different from Iranian criteria. According to Iranian cutoff points, the prevalence of underweight, overweight, and obesity are 5.2%, 9.7%, and 5%, respectively. This shows that Iranian children and adolescents are genetically lower in BMI compared to the American children and adolescents and the fifth BMI percentile was lower in Iranian children and adolescents compared to WHO and CDC fifth percentile. Figure 1 also shows the BMI distribution of children and adolescents in Lorestan province according to Iranian cutoff points, CDC, and WHO and comparisons between them.
Discussion
According to the findings of this study, the prevalence of underweight, overweight, and obesity among children and adolescents were 5.2%, 9.7%, and 5%, respectively. It was also found that boys were more likely to be overweight and obese than girls.