| Objectives:To explore the development pattern of body composition of children and adolescents,and analyze the relationship between life behavior factors and healthy body composition,so as to provide scientific evidence for promoting the healthy growth of children and adolescents.Methods:From April to December 2019,stratified cluster sampling was used to select participants.Administration districts of Guangzhou were divided into three levels according to the economic level.From each stratum,one district was selected.Then one middle school and one primary school were selected from each district,and finally a total of 11569 students aged 6-18 were investigated.Quantitative variables were described by mean±standard deviation,and qualitative variables were described by frequency and percentage.Differences between genders were compared by t test orχ2 test.The follow-up statistical analysis was analyzed separately by gender.The skewness coefficient median coefficient of variation method（LMS）was used to simulate the growth and development curves of fat mass index（FMI）,fat free body mass index（FFMI）and FM/FFM.The body composition variables were standardized according to the same age and gender,and the Z values of FMI,FFMI and FM/FFM were calculated.Taking FM/FFM as the dependent variable,Lasso regression was used to screen the life behavior variables related to body composition.Then the candidate variables were converted into two categories.Healthy behavior was recorded as 1-point,unhealthy behavior was recorded as 0-point,and the total score was calculated by gender,so as to construct the healthy life behavior score.The healthy life behavior score was divided into three levels by P33.3 and P66.7 of the same age and gender:high,medium and low.Multiple linear regression was used to evaluate the association between single life behavior,healthy life behavior score and body composition variables.The covariates adjusted in multivariate analysis were the minimum sufficient adjustment set selected by the directed acyclic graph method.Stratified analysis was performed by age groups of 6-11 years and 12-18 years,using the above methods.Results:1.The development pattern of body composition:after excluding those with lack of information and serious diseases,a total of 7888 subjects were finally included for analysis.Among them,there are 4249 boys（53.87%）and3639 girls（46.13%）.（1）Sex comparison:the FMI of boys aged 7-10 years was higher than that of girls with the same age,while the FMI of girls age>11 years was higher than that of boys with the same age（all P<0.05）.In the whole age group,the FFMI of boys was higher than that of girls of the same age（all P<0.05）.After the age of 11 years,the FM/FFM of boys was lower than that of girls of the same age（all P<0.05）.（2）Age distribution:for FMI and FM/FFM,girls show a rapid growth trend with age,while boys increase steadily from 6 to 11 years and decrease slightly after 11 years.For FFMI,both boys and girls increased with age.Before the age of 11,both boys and girls increased slowly,but after the age of 11 years,FFMI showed significant gender differences.Boys’FFMI was in a fast growth trend,while girls’FFMI was still in a slow growth trend.2.Influence of life behavior on body composition:（1）Boys:univariate and multivariate analysis showed that the intake of aquatic products（≥3 times/week）and sufficient exercise were negatively associated with FMI and FM/FFM Z value（all P<0.05）,and the intake of snacks（<3 times/week）.were positively associated with FMI and FM/FFM Z value（all P<0.05）.The intake of eggs（≥3 times/week）and sufficient exercise were positively associated with FFMI（all P<0.05）.In addition,we could not see the association between the healthy life behavior scores and their grade and FMI,FM/FFM,FFMI Z value（all P>0.05）.Stratified analysis showed that in boys aged 6-11,aquatic products（≥3times/week）were negatively associated with FMI and FM/FFM Z value（all P<0.05）.In addition,the intake of breakfast（6-7 times/week）was negatively associated with FM/FFM Z value（P<0.05）.In boys aged 12-18,the intake of milk and dairy products（≥3 times/week）and sufficient exercise were negatively associated with FMI and FM/FFM Z value（all P<0.05）,and the intake of snacks（<3 times/week）were positively associated with FMI and FM/FFM Z value（all P<0.05）.The intake of eggs（≥3 times/week）and sufficient exercise were positively associated with FFMI Z value（all P<0.05）.In addition,we could not see the association between the healthy life behavior scores and their grade and FMI,FM/FFM,FFMI Z value（all P>0.05）.（2）Girls:univariate and multivariate analysis showed that the intake of breakfast（6-7 times/week）,soft drinks（<3 times/week）were negatively associated with FMI and FM/FFM Z value（all P<0.05）,and the intake of snacks（<3 times/week）were positively associated with FMI and FM/FFM Z value（all P<0.05）.The intake of coarse grain（≥3 times/week）,snacks（<3 times/week）and sufficient exercise were positively associated with FFMI Z value（all P<0.05）.The healthy life behavior scores were negatively associated with FMI and FM/FFM Z value（all P<0.05）,and were positively associated with FFMI Z value（all P<0.05）,each score increase,FMI and FM/FFM will decrease separately by 0.02 and 0.03 standard deviation(adjustedβFMI=-0.02,95%CI=-0.04～0.00;adjustedβFM/FFM=-0.03,95%CI=-0.05～-0.01).And high healthy life behavior score was negatively associated with FMI and FM/FFM Z value（all P<0.05）,compared with the low healthy life behavior score,high healthy life behavior score has a lower FMI and FM/FFM Z value(adjustedβFMI=-0.15,95%CI=-0.25～-0.05;adjustedβFM/FFM=-0.18,95%CI=-0.29～-0.08).Stratified analysis showed that in girls aged 6-11,the intake of breakfast（6-7 times/week）,meat（≥7 times/week）,vegetables（≥7 times/week）,soft drinks（<3 times/week）were negatively associated with FMI and FM/FFM Z value（all P<0.05）.The intake of breakfast（6～7 times/week）was negatively associated with FFMI Z value（P<0.05）,and the intake of snacks（<3 times/week）was positively associated with FFMI Z value（P<0.05）.The healthy life behavior scores were negatively associated with FMI and FM/FFM Z value（all P<0.05）,each score increase,FMI and FM/FFM will decrease by 0.04 standard deviation(adjustedβFMI=-0.04,95%CI=-0.07～-0.01;adjustedβFM/FFM=-0.04,95%CI=-0.07～-0.01).And medium and high healthy life behavior scores were negatively associated with FMI and FM/FFM Z value（all P<0.05）,compared with the low healthy life behavior score,medium and high healthy life behavior scores have a lower FMI and FM/FFM Z value(Medium healthy life behavior scores:adjustedβFMI=-0.19,95%CI=-0.32～-0.05、adjustedβFM/FFM=-0.19,95%CI=-0.32～-0.05;High healthy life behavior scores:adjustedβFMI=-0.24,95%CI=-0.41～-0.08、adjustedβFM/FFM=-0.25,95%CI=-0.41～-0.08).In girls aged 12-18,the intake of breakfast（6～7 times/week）and fine grain（≥7times/week）were negatively associated with FMI and FM/FFM Z value（all P<0.05）,and the intake of snacks（<3 times/week）was positively associated with FMI and FM/FFM Z value（all P<0.05）.The intake of egg（≥3 times/week）and snacks（<3 times/week）were positively associated with FFMI Z value（P<0.05）.In addition,appropriate video viewing was negatively associated with FM/FFM Z value（P<0.05）.The healthy life behavior score was positively associated with FFMI Z value（P<0.05）,each score increase,FFMI will increase by 0.02 standard deviation(adjustedβFFMI=0.02,95%CI=0.00～0.05).Conclusions:1.The development of body composition of children and adolescents in Guangzhou has gender specificity.Before the age of 11 years,the adipose tissue and fat-free tissue development trend of boys and girls are similar;After the age of 11 years,the adipose tissue of girls increases significantly,and the increase of weight growth is due to the joint contribution of fat-free tissue and adipose tissue development.The fat-free tissue of boys increases rapidly,and the weight growth is mainly due to the contribution of fat-free tissue development,and thus the utility of BMI in boys may lead to the overestimation of obesity.2.In boys,regular intake of aquatic products,dairy products,eggs and sufficient exercise are associated with the increase of FFMI or the decrease of FMI;In girls,intake of breakfast,fine grain,meat and vegetables every day,regular intake of coarse grain,aquatic products,eggs,less intake of soft drinks,snacks and sufficient exercise are associated with the increase of FFMI or the decrease of FMI.3.In girls,the healthy life behavior scores and their grades are associated with the increase of FFMI or the decrease of FMI.Above findings need to be further verified by prospective research. |
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