How to Measure Body Composition
Body composition refers to every tissue within the human body. The tissues within your body are divided into two major categories:
• lean body tissue (muscle and body organs)
• body fat levels (fat)
Just as you have muscles, bones, and organ systems running through your body, fat is also found deep within your body as well as between your muscles and your skin. For optimal health, your body needs some body fat but it should be a small percentage of your overall body composition.
Tests have been developed to measure body composition. Most methods of body composition measurement were developed using healthy individuals and may have limited use for those in extreme populations. These methods have also been developed based upon certain assumptions which may need to be considered when interpreting your body composition results, such as water and electrolyte concentrations, body tissue density, and how body components and tissues interrelate and are distributed throughout a healthy individual.
There are three major categories for measuring body composition consisting of several methods.
As the most basic method in assessing body composition, indirect methods describe body mass, size, shape, and level of fat.
• Skin fold - Using calipers, the thickness of the skin is measured, and then used to provide an estimate of the total amount of body fat.
• Height-Weight and Body Mass Index (BMI) Charts developed using extensive national reference data indicate normal weight ranges according to age and sex. They are inaccurate for individuals with a high percentage of muscle, such as athletes.
• Abdominal Measurements - Commonly known as waist measurements or or waist-to-hip ratios, this method is more indicative of overall health risks.
• Bioelectrical Impedance Analysis (BIS) Using a small electrical current, BIA estimates total body water, fat mass, and fat-free mass.
Direct methods measuring body composition focus on specific, identifiable aspects within the body. These tests usually occur in a clinical setting.
• Total Body Water (TBW) - Also known as hydrometry or isotope dilution, TBW measures your water levels before, during, and after drinking a deterium-isotope dilution. This method assumes that the patient is properly hydrated.
• Total Body Counting - Often known simply as body counting, this method measures radioactive potassium 40 (40K) which occurs naturally within your body.
• Neutron Activation - Using neutron radiation, gamma output will measure many elements found within your body, such as carbon, sodium, calcium, and especially nitrogen, which is used to predict the amount of proteins in the body.
These methods of body composition are based on the measurements of two or more variables
• Dual Energy X-Ray Absorptiometry (DXA) - Originally developed to measure bone density, DXA also calculates the values of fat and fat-free mass.
• Underwater Weighing (Hydrodensitometry) - This method compares your weight on land with your weight under water with adjustments made for your air lung capacity.
• Air Displacement Plethysmography or Bod Pod Similar to underwater weighting, this method measure the amount of air displaced as you sit within a chamber, often called a Bod Pod.
• Magnetic Resonance Imaging (MRI) and Computed Topography (CT) Like DXA, MRIs and CT scans can be used to measure areas of the body and the entire body.
Measuring your body composition can be very informative and helpful in assessing your overall health. Some of these methods allow you to make self-assessments while others require clinical professionals.
Duren, Dana L. et al. Body Composition Methods: Comparisons and Interpretation. J Diabetes Sci Technol 2008;2(6):1139-1146
Wells, JCK and MS Fewtrell. Measuring Body Composition. Arch Dis Child 2006;91:612-617