This study presents reference values for body composition and bone mineral density derived from the National Health and Nutrition Examination Survey (NHANES) using dual-energy X-ray absorptiometry (DXA). The data, collected from 1999 to 2004, includes measurements for adults and children, normalized to age, height, or lean mass. Reference values were developed for %fat, fat mass/height², lean mass/height², appendicular lean mass/height², %fat trunk/%fat legs ratio, trunk/limb fat mass ratio, bone mineral content (BMC), and bone mineral density (BMD). These values are useful for evaluating abnormalities in fat, lean, and bone mass, establishing clinical trial entry criteria, and for medical, research, and epidemiological purposes. An obesity classification scheme was developed using Fat Mass Index (FMI), which is fat mass divided by height squared. This index is more specific than body mass index (BMI) as it focuses on fat mass rather than total body weight. The reference values are based on the NHANES dataset, which includes data from three major ethnic groups: Non-Hispanic Whites, Non-Hispanic Blacks, and Mexican Americans. The study also highlights the importance of fat distribution, including indices such as %fat trunk/%fat legs and trunk/limb fat mass ratio, in assessing metabolic syndrome and lipodystrophy. The data were analyzed using the LMS curve fitting method, which is suitable for handling skewed data. The method involves normalizing the data and fitting curves to generate reference values. The study found that FMI classifications are more accurate than BMI for identifying obesity, as they are based on fat mass rather than total body weight. The reference values were validated using statistical methods and showed good fit with the data. The study also discusses the limitations of BMI, including its inability to account for gender and ethnicity, and the potential for misclassification in certain populations. The FMI classifications presented in the study are based on prevalence data and may misclassify fewer individuals than BMI. The study recommends using FMI for obesity classification, particularly in children, where height normalization is appropriate. The reference values are also useful for detecting abnormalities in lean mass accrual and bone-muscle unit function in children. The study emphasizes the importance of using age and height-specific reference values for accurate assessment of body composition and bone density in children.This study presents reference values for body composition and bone mineral density derived from the National Health and Nutrition Examination Survey (NHANES) using dual-energy X-ray absorptiometry (DXA). The data, collected from 1999 to 2004, includes measurements for adults and children, normalized to age, height, or lean mass. Reference values were developed for %fat, fat mass/height², lean mass/height², appendicular lean mass/height², %fat trunk/%fat legs ratio, trunk/limb fat mass ratio, bone mineral content (BMC), and bone mineral density (BMD). These values are useful for evaluating abnormalities in fat, lean, and bone mass, establishing clinical trial entry criteria, and for medical, research, and epidemiological purposes. An obesity classification scheme was developed using Fat Mass Index (FMI), which is fat mass divided by height squared. This index is more specific than body mass index (BMI) as it focuses on fat mass rather than total body weight. The reference values are based on the NHANES dataset, which includes data from three major ethnic groups: Non-Hispanic Whites, Non-Hispanic Blacks, and Mexican Americans. The study also highlights the importance of fat distribution, including indices such as %fat trunk/%fat legs and trunk/limb fat mass ratio, in assessing metabolic syndrome and lipodystrophy. The data were analyzed using the LMS curve fitting method, which is suitable for handling skewed data. The method involves normalizing the data and fitting curves to generate reference values. The study found that FMI classifications are more accurate than BMI for identifying obesity, as they are based on fat mass rather than total body weight. The reference values were validated using statistical methods and showed good fit with the data. The study also discusses the limitations of BMI, including its inability to account for gender and ethnicity, and the potential for misclassification in certain populations. The FMI classifications presented in the study are based on prevalence data and may misclassify fewer individuals than BMI. The study recommends using FMI for obesity classification, particularly in children, where height normalization is appropriate. The reference values are also useful for detecting abnormalities in lean mass accrual and bone-muscle unit function in children. The study emphasizes the importance of using age and height-specific reference values for accurate assessment of body composition and bone density in children.