obesity is due to an unbalanced energy equation . worldwide , obesity is a leading cause of morbidity and mortality , and its prevalence has nearly doubled in the recent years [ 2 , 3 ] . burden of obesity disorders , as well as its prevalence and incidence , is increasing in asia . many studies have demonstrated a high prevalence and increasing trend for obesity in iranian people [ 5 , 6 ] . however , investigating trajectories of change in obesity , over time , is always a major concern for researchers and the previous obesity trend studies , in our country , considered only individual changes to investigate trajectories without considering the families effects . body mass index ( bmi ) , defined as weight divided by height squared , is a quantitative measure of obesity . several measures , as waist circumference ( wc ) and its derivatives , were developed for amplifying bmi that also consider the body shape . however , the strong correlation between wc and bmi makes it problematic to estimate the excess risks . to overcome this defect , in 2012 , n. y. krakauer and j. ( absi ) , by adjusting for wc with bmi and height , and concluded that absi is a better predictor for premature mortality hazard , in the american population sample , than bmi and wc . in the study , obesity was measured by three common indicators , bmi and wc and , a new one , absi . the aim of the study is to assess the shape of trajectories of change in obesity indices , bmi , wc , and absi , in tehranian families that participated in the tehran lipid and glucose study ( tlgs ) , using multilevel latent growth curve modeling ( mlgcm ) approach . specifically , we investigated the longitudinal changes in the measurements , across 12 years , within and between families , relation between initial status and growth rate of the indices within individuals or families , and , also , effects of age and sex on the growth rate of obesity indices . the tlgs is an ongoing longitudinal large - scale community - based study , with a 3-year follow - up period , designed to estimate the prevalence of noncommunicable disorders ( ncd ) and included a representative sample of residents of 13 districts of tehran , capital of iran . the tlgs has been implemented in a multistage stratified ( district ) cluster ( families ) random sampling technique , to select more than 15000 people aged > 3 years , from march 1999 to december 2001 . phases ii , iii , and iv were prospective follow - up studies and were performed from 2002 to 2004 , 2006 to 2008 , and 2009 to 2011 , respectively [ 9 , 10 ] . a total of 14761 individuals ( valid case ) were selected from the total participating cases in tlgs , including 3980 families , with an average number of 3.38 individuals , among phase i ( baseline ) . at each phase , individuals with at least one valid value for the anthropometric indices entered the analysis . in more detail , the tlgs protocol was approved by the research institute for endocrine sciences , shahid beheshti university of medical sciences , tehran , iran . the anthropometric indices measured included weight ( kg ) , height ( m ) , and waist circumference ( cm ) . using the world health organization standard protocol , wc was measured at the approximate midpoint between the lower margin of the last palpable rib and the top of the iliac crest , by the trained physicians . first descriptive data , depicted in table 1 , including mean and standard deviation ( sd ) of quantitative variables and sex ratio , were reported . to assess the normal distribution of each measurement , among study time points , skewness , kurtosis , and its standard error , as well as q - q plot , were used . also , to compare magnitude of explained variation between and within families of each outcome , we used intraclass correlation coefficient ( icc ) at each time point . then , we conducted a trend analysis , by repeated measures analysis of variance ( anova ) technique and tested the linear and quadratic trend among four time points . since , for individuals of the tlgs data cluster in families , the multilevel analysis was considered and because the outcomes are measured in four time points , data analysis was conducted using mlgcm in three - level framework ( time , individual , and family ) . the mlgcm is a flexible way to analyze latent growth curves , combining structural equation modeling ( sem ) and multilevel modeling [ 1113 ] . the mlgcm can incorporate factor analysis and can test variety of causal effects in the sem framework in longitudinal complex data . these models were fitted in mplus version 6.12 ( l. muthn and b. muthn , los angeles , ca , usa ) . for diagnosis of the best shape of changes in the longitudinal multilevel structure data , we performed a strategy in three steps and then the interpretation is according to the preferred model , adjusted for age and sex . the effect of age and sex is considered on the intercept and slope of growth . the most common overall fit index in the literature is the mplus robust maximum likelihood chi - square test that is robust to depart from the normality assumption . also , jreskog suggested using ratio /df , as a descriptive index to compare models . to avoid sample size and model complexity dependency problems , the nonnormed fit index ( nnfi ) and root mean square error of approximation ( rmsea ) are commonly used [ 17 , 18 ] . to evaluate multilevel structural equation model standardized root mean square residual ( srmr ) for between model the cutoffs for the ratio /df , rmsea , srmr , nnfi , and confirmatory fit index ( cfi ) are 02 , 0.05 , 0.09 , 0.97 , and 0.97 , respectively , and for acceptable fit , they are 2 - 3 , 0.08 , 0.1 , 0.95 , and 0.95 , respectively , . the mean age  sd of the individuals in the present study , at baseline , was 33.28  19.01 ( range 389 years ) and 50.1% were male . descriptive statistics of age , gender , and anthropometric measurements , for each phase , have been shown in table 1 . based on repeated measures anova model for assessing polynomial mean contrasts , the linear and quadratic trend were significant ( p < 0.001 ) . also , the intraclass correlation coefficients for the three anthropometric measurements are ranged within 0.040.13 . also , it is evidenced to consider the family effect of the participant in our data analysis . by taking into account our large sample size , the estimated skewness and kurtosis values , as well as the shape of q - q plots , suggested that there is no major departure from the normal distribution of the variables . results of the three - step strategy , for model building , are summarized in table 2 . the first model was used to test whether the anthropometric measurement changed or not during the studied phases . because the model ignored the two - level structure of the data for all three anthropometric measurements , the ratio /df is very large , rmsea , cfi , nnfi and srmr suggesting that this model has acceptable fit to the data , although not good for analysis . however , this result is , without regard , multilevel data structure . as shown in table 1 , iccs of the anthropometric measurements are ranged within 0.070.13 , 0.050.15 , and 0.040.09 for bmi , wc , and absi , respectively . step  2 ( models  2 and 3 ) : unconditional mlgcm ( linear and quadratic shape ) . the unconditional mlgcm , in the linear ( model 2 ) and quadratic ( model 3 ) forms , was checked for type of trend shape within multilevel framework . as would be found in table 2 , among three anthropometric measurements , the ratio /df is considerably decreased , compared to the conventional lgcm , in step 1 ( model 1 ) , while still remaining high . also , rmsea , cfi , nnfi , and srmr suggest that this model has acceptable fit to the data , although not good . also , in contrast to model 3 , model 2 has clearly better fit . step  3 ( model  4 ) : conditional mlgcm assessment . after perusing the two preceding steps to examining trends and shape , in this step , we adjusted the model for the effects of age and gender on intercept and slope of the trajectory . as shown in table 2 , across anthropometric measurements , conditional linear mlgcms have a better fit than the unconditional linear format . the results of the model building strategy preferred the conditional mlgcm , adjusting for age and sex . the growth rate means are positive , as expected , and significantly different from 0 . among these three means , variations of initial status in three measurements are significant on individual and family level , as expected . also , this is true for variations of growth rates of the three measurements , on both individual and family levels , except absi on family level . there is a significant correlation between initial status and growth rate , for each of the three measurements , on both individual and family levels , except absi on family level . these significant correlations for bmi and wc are negative and positive , for individual and family level , respectively . this indicated that the most obese individuals had a lower rate of increase and families with a high degree of initial obesity had a faster rate of increase . in all three anthropometric measurements , gender effect on initial status and growth rate is significant , while this effect on bmi is positive and negative on wc and absi . this means that the initial measurement of bmi and its rate of growth in female subjects are greater than in males , while this is opposite for wc and absi . also , the range of r - square of the model for bmi and wc is more than 84% , whereas for absi it is less than 65% . in this study , we used mlgcm adjusted for age and sex on long - term bmi , wc , and absi status on tlgs , for investigating obesity trajectories in change of obesity between and within tehranian families . our essential findings were ( 1 ) obesity among tehranian people has significantly increased , ( 2 ) individuals with more fat become obese slower , while families with more fat become obese faster , and ( 3 ) obesity trajectory in men and women is significantly different , while initial value and growth rate of wc and absi in men are greater than in women , and , in the meantime , the initial value and growth rate of bmi in men are lower than in women . since the wc and absi are included in body shape , as well as fat , we concluded that , in tehranian people , men are more obese and have faster growth rates in terms of body shape than women . however , in terms of fat , without regarding the body shape , the situation is worse for women than men . similar to the present study , several previous reports have shown that obesity is escalating rapidly , in most countries , in the past three decades [ 2 , 3 ] . however , the studies concerning bmi showed that , in developing countries , obesity level for women is higher than for men , similar to our study . assessed obesity and abdominal obesity by bmi , wc , and waist - to - hip ratio , based on the 3 first phases of tlgs . they used a logistic model for each phase and demonstrated an increasing in prevalence of obesity and abdominal obesity in tehranian people . investigated obesity through a meta - analysis in iran , based on 58 studies , and demonstrated that obesity prevalence in women is greater than in men and rates increase with age , especially in women . our study found obesity trajectories among families by mlgcm in a wide age interval by adjusting the effects on intercept and slope of the trajectory . also the age effect could be adjusted by stratification in a new model as multigroup analysis ( mga ) approach . second , according to our knowledge , because absi has been introduced recently , there is no study to investigate the obesity trajectory by the indicator . in longitudinal studies , we used full information maximum likelihood approach to conduct missing at random mechanism that is more efficient and has less bias , compared to common methods , such as mean imputation , listwise and pairwise deletion . in summary , the present study , despite significant differences between families , suggested that the obesity trend among the tehranian people and their families is alarming and , therefore , the burden of obesity in the near future will be problematic . therefore , there is a need for public health interventions and approaches to lifestyle modification , which can address this emerging crisis , and we believe that these public health programs should be more family centered .
objectives . to evaluate the trajectories of change in obesity within and between tehranian families , who participated in the tehran lipid and glucose study ( tlgs ) . methods . 
 this study is a family - based longitudinal design , in four waves . 
 a total of 14761 individuals , within 3980 families , were selected . 
 three anthropometric measurements , body mass index ( bmi ) , waist circumference ( wc ) , and a body shape index ( absi ) , were recorded . 
 multilevel latent growth curve modeling ( mlgcm ) approach was used for evaluating the change trajectories in obesity within and between the families . 
 results . the mean age of the subjects in the present study was 33.28  19.01 ( range 389 years ) and 50.1% were male . 
 obesity was significantly increased ( p < 0.001 ) . 
 individuals with more fat become obese slower , whereas families with more fat become obese faster ( p < 0.001 ) . 
 the initial value and growth rate of wc and absi were greater in men than in women , while this result is contrary to bmi ( p < 0.001 ) . 
 conclusions . 
 our findings demonstrated that there is an alarming increase in the obesity trend in tehranian families . 
 the important role of the family in the prevention of obesity is highlighted , underlining the need for public health programs , as family centered educations to lifestyle modification , which can address this emerging crisis .