| ObjectiveHuman body composition refers to the content of various compositions in the human body?such as fat,muscle and bone,etc.?,which reflects the accumulation of nutrients in the human life process and the nutrients obtained from the external environment to build the body's quality,form and function.Children and adolescents are in the critical period of physical shaping where fat,muscle and bone will change significantly.These change in body composition is closely related to future health.Moreover,the prevalence of overweight and obesity among children and adolescents in China is accelerating and has become a major public health problem.At present,scholars have used body composition to assess the degree of obesity and growth status in children and adolescents.But most studies ignored the close coupling and mutual influence of fat-muscle-bone.From medical statistics view,the relative quantity data of body composition about fat-muscle-bone as a structural whole?fat percentage,muscle percentage,bone mineral percentage?was multivariate compositional data?CoDA?of unit-sum constraint?i.e.the sum of all composition ratios was 1?.For such data,classical statistical analysis methods may lead to problems such as pseudo-correlation,inconsistency with reality,or difficulty in interpretation.Therefore,this study would adopt the CoDA method to explore the body composition distribution characteristics and its influencing factors in children and adolescents,which could take fat-muscle-bone as a structural whole.Moreover,simulation study about CoDA would be conducted to explore the applicability about CoDA method,which mean the impact of different parameters on fitting effect of CoDA method.And the effectiveness of CoDA method applied to body compositon analysis was further verified.MethodsIn this study,three CoDA methods,including Isometric Log Ratio?ILR?,Dirichlet distribution,and Flexible Dirichlet?FD?model,were used to analyze the ratio distribution of body composition?fat,muscle and bone mineral?,various parts?upper limb,lower limb,and trunk?about fat and muscle in 6 to18 years children and adolescents from Guangzhou,China.Then according to the goodness of fit index,the best optimal fitting method was selecting to describe distribution characteristics of body composition,various parts about fat and muscle in children and adolescents.The variation matrix was calculated to reflect the correlation between the compositions.And 95%reference contour region?RCR?about the ratio of fat,muscle and bone mineral,various part about fat and muscle in children and adolescents was established.Further,CoDA regression model was constructed to analyze the influencing factors of fat relative dominance?FRD?,muscle relative dominance?MRD?and bone relative dominance?BRD?about body composition in children and adolescents.Finally,based on the distribution of the optimal CoDA method,CoDA was simulated under different parameters?sample size,composition number,composition ratio,composition variance,and correlation coefficient between compositions?,exploring the effect of each parameter and combination on on fitting effect of CoDA method.Results1.Based on the goodness of fit index,ILR method was selected to analyze the body composition distribution characteristics and influencing factors in children and adolescents.The study results of body composition distribution in children and adolescents showed that fat mass,muscle mass and bone mineral content in boys and girls increased with age.After 12 years old,the fat mass of boys was significantly lower than the girls,and the muscle mass of boys was significantly higher than the girls.The fat percentage in boys increased before the 12 years old,decreased in the age of 12 to 15,and went up with age after 16 years old.Girls'fat percentage increased with age.The muscle percentage in boys decreased with age,but increased after trough in 11 years old,and rase again after peak in 15 years old.The muscle percentage of girls decreased each year.Relative to the percentage of fat and muscle,the change with age about bone mineral percentage was less in boys and girls.But the overall trend was declining.After 12 years old,the fat percentage was significantly lower,while muscle percentage was significantly higher in boys than girls.There was strong correlation between muscle and bone mineral percentage.And 95%RCRs of fat,muscle and bone mineral percentage in children and adolescents at age 6-7 years were[4.11-30.69%],[64.69-90.69%],[4.62-6.93%]for boys;[4.11-29.69%],[65.69-90.11%],[4.62-5.77%]for girls,respectively.The 95%RCRs of percentage about fat,muscle and bone mineral in children and adolescents at age 17-18 years were[14.69-28.69%],[66.69-80.69%],[4.62-4.62%]for boys;[15.11-47.27%],[49.27-79.11%],[3.46-5.77%]for girls,respectively.2.The study results of various parts distribution about fat in children and adolescents showed that the upper limb,lower limb,and trunk fat mass of boys displayed an upward trend with increasing age before the age of 12 and after the age of 16,and a downward trend at the age of 12-15.The various part fat mass in girls gradually increased with age.After 12 years old,the various part fat mass was significantly lower in boys than girls.But the upper and lower limb fat percentage decreased,and trunk fat percentage increased with age in boys and girls.Before 11 years old and after 15 years old,the upper limb fat percentage of boys was lower than girls,while was higher at other ages than girls.The lower limb fat percentage of boys was higher than or closed to girls.The trunk fat percentage of boys was higher than girls before10 years old,and it was lower after that than girls.The upper limb fat percentage was strongly correlated with lower limb fat percentage in boys and girls.And the 95%RCRs of upper limb,lower limb,and trunk fat percentage in children and adolescents at age 6-7 years were[12.75-33.27%],[36.17-78.85%],[1.15-49.65%]for boys;[14.79-34.69%],[41.22-79.85%],[1.15-42.72%]for girls,respectively.The 95%RCRs of upper limb,lower limb,and trunk fat percentage in children and adolescents at age 17-18 years were[8.75-18.64%],[26.40-58.99%],[28.87-62.35%]for boys;[12.17-19.48%],[30.44-44.22%],[41.57-54.27%]for girls,respectively.3.The study results of various parts distribution about muscle in children and adolescents showed that the upper limbs,lower limbs and trunk muscle mass in boys and girls displayed an upward trend with age.After 12 years old,the various part muscle mass of boys was significantly higher than the girls.The upper limb muscle percentage decreased each year before the age of 10,but it was increased after that in boys and girls.On the whole,the lower limb muscle percentage increased,and the trunk muscle percentage was decreased with age in boys and girls.The upper and lower limb muscle percentage in boys was higher than or close to girls,and the trunk muscle percentage of boys was lower than girls.There was a greater correlation between the various parts muscle percentages in boys and girls.And the 95%RCRs of upper limb,lower limb,and trunk muscle percentage in children and adolescents at age 6-7 years were[7.65-11.29%],[30.98-39.02%],[51.96-60.04%]for boys;[7.13-11.29%],[31.56-37.29%],[54.27-60.04%]for girls,respectively.The 95%RCRs of upper limb,lower limb,and trunk muscle percentage in children and adolescents at age 17-18 years were[10.17-12.17%],[37.60-42.33%],[47.34-50.81%]for boys;[8.44-12.02%],[34.86-41.17%],[49.65-54.27%]for girls,respectively.4.The study results of the influencing factors about body composition in children and adolescents showed that birth weight(?FRD=0.06;?MRD=-0.03),father BMI(?FRD=0.05;?MRD=-0.02;?BRD=-0.02),and mother BMI(?FRD=0.05;?MRD=-0.02;?BRD=-0.02)were positively related to fat relative dominance,and negatively related to muscle or bone relative dominance for boys?all P?0.039?.Age(?13 years vs.10-12 years,?FRD=-0.33;?MRD=0.20;?BRD=0.13),aquatic products intake(3-5 times/week vs.<1 time/week,?FRD=-0.19;?MRD=0.10;?BRD=0.10),and pure milk intake(<1 time/week vs.never,?FRD=-0.26;?MRD=0.13;?BRD=0.12)were significantly associated with a lower fat relative dominance,a higher muscle relative dominance,and bone relative dominance in boys?all P?0.032?.The bone relative dominance of boys was higher in the?1 time/week group than never eating group about milk powder(?BRD=0.11,P=0.023).Similarly,age(?13 years vs.10-12 years,?FRD=0.36;?MRD=-0.18;?BRD=-0.18),birth weight(?FRD=0.09;?MRD=-0.04;?BRD=-0.04),father BMI(?FRD=0.03;?MRD=-0.02;?BRD=-0.02),and mother BMI(?FRD=0.05;?MRD=-0.03;?BRD=-0.03)were positively correlated with fat relative dominance and negatively correlated with muscle relative dominance and bone relative dominance for girls.Compared with the girls who never ate milk powder,the girls in the?1 time/week group had lower fat relative dominance(?FRD=-0.14,P=0.042)and higher muscle relative dominance(?MRD=0.07,P=0.047).In contrast,compared with<1 time/week group about the eggs/duck eggs or other eggs,girls in the other groups had higher fat relative dominance(all?FRD?0.20,P?0.010),lower muscle relative dominance(all?MRD?-0.09,P?0.015)and bone relative dominance(all?MRD?-0.11,P?0.009).5.Regardless of the number of compositions?2 compositions,3compositions,and 4 compositions?,the study results of compositional data simulation showed that the fitting effect of compositional data,which met a larger sample size,larger differences between composition ratio,smaller variance of composition,and larger value of correlation coefficients between compositions,was better by using ILR method.ConclusionILR method could better analyze body composition characteristics and influencing factors.There were aged differences of fat-muscle-bone percentage,various part percentage about fat and muscle in boys and girls.The study further established 95%reference contour region of fat-muscle-bone percentage,various part percentage about fat and muscle in different ages in children and adolescents.The influencing factors of body composition in children and adolescents included age,gender,birth weight,father BMI,mother BMI,aquatic products,eggs/duck eggs or other eggs,pure milk,and milk powder.The results of this study could provide reference for the growth and development assessment of children and adolescents,and scientific basis for the development of dietary guidelines for children and adolescents. |
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