Introduction

Dual energy x-ray absorptiometry (DXA) has long been accepted as the primary method for measuring bone mineral content and bone mineral density because of its high precision, accuracy, and low radiation exposure. More recently, whole body DXA has become a valuable method of measuring body composition due to its speed, ease of use, and strong correlation with criterion methods of assessing body composition. In addition, DXA has been shown to be comparable in reliability and accuracy to alternative methods of assessing body composition in defined body regions. The assessment of body composition by DXA has taken on added importance as the prevalence of obesity in the United States over the past 40 years has increased steadily among both adults and children.

National Health and Nutrition Examination Survey (NHANES)

Although BMI (Body Mass Index), which is calculated based on weight and height, has been used as the standard measure of obesity in the United States and other countries, there are recognized limitations to the use of BMI in assessing obesity since the relationship of body fat to BMI varies with age, sex, ethnicity, and physical conditioning. Because DXA assesses the proportions of fat mass and fat-free mass in the body, it can provide a more accurate measure of body fat than BMI is able to do. The National Health and Nutrition Examination Survey (NHANES) implemented whole body DXA scans of survey participants age 8 years and older to provide nationally representative data on body composition and data to study the association between. body composition and other health conditions and risk factors, such as cardiovascular disease, diabetes, hypertension, and activity and dietary patterns. NHANES are conducted by CDC, National Center for Health Statistics (NCHS). The results of this study are valuable not only for understanding the subject of body composition, but also for providing context to DXA scan results to any individual completing the scan. This includes how the individual compares with the rest of the population based on age, sex, and race and ethnicity.

Average (mean) body fat percentage by age, sex, and race and ethnicity.

Selected Highlights

• Females had higher percentage body fat than males at all ages.

• Among males overall and within each of the three male race and ethnic groups, percentage body fat was lowest at ages 16–19 years.

• Among females overall and in non-Hispanic white and non-Hispanic black females, percentage body fat was lowest at ages 8–15 years.

• Among males overall and in non-Hispanic white and non-Hispanic black males, percentage body fat was highest at ages 60–79 years and older.

• Among females overall and in non-Hispanic white females, percentage body fat was highest at ages 60–79 years.

• Non-Hispanic black males had lower percentage body fat than either non-Hispanic white males or Mexican-American males from ages 8–11 years through 60–79 years.

  At 80 years of age and older, there were no differences in percentage body fat among the three race and ethnic groups.

• Mexican-American females had higher percentage body fat than non-Hispanic black females from ages 8–11 years through 16–19 years and higher than non-Hispanic white females from ages 12–15 years through 40–59 years.

  From age 60 years and older, there were no differences in percentage body fat among the three race and ethnic groups.

Source: Body Composition Data for Individuals 8 Years of Age and Older: U.S. Population, 1999–2004

Review a simplified body fat percentage chart.