A: There are many methods of estimating body fat. The following is a summary of the most common ones.
DEXA (Dual Energy X-ray Absorptiometry)
Today, this method is considered a gold standard because of its reliability, precision, and the fact that it is based on three body components (fat, muscle, bone) rather than two (fat and muscle) as in most other methods including hydrostatic weighing. It allows fat distribution throughout the entire body to be read in a single scan. The equipment used is very expensive and a person must lie perfectly still for 10-20 minutes while the scan is taken. DEXA is found mainly in research facilities.
Done correctly, this method is also quite accurate and considered a gold standard. However, the test is somewhat subjective because it relies upon the subject’s ability to expel all oxygen from their lungs while submerged in a tank of water. Oxygen remaining in the lungs will skew the results. In clinical settings, this procedure is repeated a number of times, and an average is taken. The “tank” is expensive and the inconvenience to the user is considerable. Because of the cost, lengthy testing process, and physical burden to the subject, this method is more suitable for research studies.
Bioelectrical impedance analysis uses a very small electrical signal to measure body impedance. The signal is conducted through the water contained in the body. Lean muscle has much more water than fat tissue and allows the signal to pass easily. Fat causes impedance or resistance to the signal. Conventional Bioelectrical Impedance Analysis methods are accurate, though not as convenient as the Tanita BIA method, and may be somewhat subjective based on the placement of electrodes. The user must be in a horizontal position while electrodes and conductive jelly are placed on a wrist and ankle. This procedure is usually performed in a physician’s office or clinic. Most conventional BIA manufacturers use hydrostatic weighing as the reference method.
Tanita’s leg-to-leg version of BIA produces very accurate results that are highly correlated with both DEXA (Tanita’s reference method) and hydrostatic weighing. Measurements are very repeatable when tests are performed under consistent conditions. The equipment is not expensive, making Tanita a professionally-accepted method that can be adapted easily for home use. There is no physical imposition to the user; no need for a trained technician to operate the equipment; and the entire procedure takes less than one minute.
Skinfold measurements taken by calipers are easy to do, inexpensive, and the method is portable. However, results can be very subjective depending on the skill of the technician and the site(s) measured. The quality of the calipers is also a factor. Inexpensive models sold for home use are usually less accurate than those used by an accredited technician. Additionally, the more obese the subject, the more difficult to “pinch” the skin correctly. Many people find calipers to be uncomfortable and invasive.
(Near Infra-Red) A fiber optic probe measures tissue composition at various sites on the body. This method has become popular because it is simple, fast, non-invasive, and the equipment is relatively inexpensive. However, studies have produced mixed results, and a high degree of error has occurred with very lean and very obese people. Numerous sources report that more research is needed to substantiate this method.