Knowing your body composition is useful for several reasons, especially when trying to lose weight or train for an athletic event. Many exercise physiologists would agree that tracking changes in percent body fat is essential to meeting weight and training goals.
However, with all of the techniques currently used to determine body composition, it can be confusing to decide which technique to use. It's important to know each option and their downfalls.
Hydrostatic (underwater) weighing was the gold standard once upon a time. While it produces results that only error 1-2%, the ability to achieve such results is difficult and dependent on patient skill. During underwater weighing, the participant must exhale all air from their lungs and sit completely submerged in water until the measurement is complete. Not only is this challenging to do right, but it's also very uncomfortable.
Skinfolds are very popular among many trainers due to the lack of equipment needed. Much like hydrostatic weighing, though, accurate results require a high skill level. The technician must collect skinfold data from exactly the right site and ensure they measure only fat and skin. The ability to do that correctly is not common, and even with the best technique, there's still an error of 2-4%.
Bioelectrical Impedance (BIA) is also commonly used among trainers and physiologists. While the technique, when done with 4-limb electrodes, produces decent results, most places use either a hand-to-hand or leg-to-leg device. BIA measures electrical current through water in lean issue as opposed to fat, so going from leg-to-leg results in a reading on only the lower half of the body. Most people are not exactly proportional between upper and lower body, so the estimated results are inaccurate.
Dual Energy X-ray Absorptiometry (DXA) is the current gold standard for body composition assessments. It obtains results with only 0.5-2% error. Unlike the previous mentioned methods that are 2-component, it is based on a 3-component model, meaning it assumes body mass consists of fat mass, lean tissue, and bone mineral as opposed to just fat mass and fat-free mass. In addition, participation from the patient is minimal, as they only need to lay still while the scan runs. It's only downfall is that it assumes lean tissue hydration is a constant 73%. This is true for most healthy individuals but can result in error if the person is over or dehydrated. That is simple enough to fix, though - just hydrate properly before the test.
Dr. David Carfagno is a Board Certified Internist and Sports Physician, who trained at the Cleveland Clinic Foundation
1. Horber, F. (1992). Impact of hydration status on body composition as measured by dual energy x-ray absorptiometry in normal volunteers and patients on haemodialysis. British Journal of Radiology, 65(778), 895-900.
2. Kirkendall, D., et. also. (1991). Field comparison of body composition techniques: Hydrostatic weighing, skinfol thickness, and bioelectrical impedance. Journal of Orthopaedic & Sports Physical Therapy, 13(5), 235-9.
3. Lohman, T., et. al. (2000). Assessing body composition and changes in body composition: Another look at dual-energy x-ray absorptiometry. Annals of the New York Academy of Sciences, 904, 45-54.