Login or Register

What Is the Most Accurate Way to Measure Body Fat?

Mar 28, 2011 | By Deirdre Denholm
What Is the Most Accurate Way to Measure Body Fat?
Photo Credit x-ray of bones image by Tammy Mobley from Fotolia.com

Most methods of measuring body fat have some margin of error. Accurate measures consider more variables. Dehydration and extreme body fat can distort results. Approaches to determining body composition and fat concern the number of components, or compartments, measured. For example, a two-compartment model measures bone and the rest of body mass, while a three-compartment model determines bone, lean mass and fat. A four-compartment model measures fat and breaks lean mass down into water, protein and mineral components. The most accurate way of measuring body fat is dual energy X-ray absorptiometry, or DXA, based on at least a three-compartment model.

What Is Dual Energy X-Ray Absorptiometry?

Dual energy x-ray absorptiometry, used in medical diagnosis and for clinical research typically measure bone density. However, DXA can measure entire body composition according to a three- or four-compartment model. During a scan you lie down and a scanner above you moves over your entire body. The scanner emits at least two energies of radiation beams, which calculates differences between the amounts of certain tissue depending on the rate of energy absorption of each beam.

Advantages of DXA

A DXA scan takes slightly more than 10 minutes to complete and does not require any contact with your body. You can remain comfortable and fully clothed during the scan, but you must not wear any metal. The results of the scan can give you an analysis of not only the amount of body fat but also the amount of lean body mass and the density of your bones. It is useful to know the amount of lean mass, especially if you are planning to lose weight. You can then determine how much fat you are losing compared with lean mass. According to an article by Miriam Bredella and colleagues published in the November 2010 issue of the journal "Obesity," DXA results are not dependent upon the amount of body hydration, except in the region of the thigh, where it may underestimate the amount of fat.

Disadvantages of DXA

DXA involves exposure to low levels of radiation, and this risk must be taken into account. The test should not be done if you are pregnant. DXA can be somewhat expensive, ranging from about $75 to $300. You must find a clinic offering this type of body composition analysis, which may not be available in some geographical areas. DXA may not be able to measure extremely obese people, due to equipment limitations. The study by Bredella also points out that DXA may not be accurate when measuring "markedly obese women."

DXA Accuracy Compared With Other Measures

While CT and MRI scans are accurate when measuring body composition in some people, they are impractical for wide spread use in measuring body fat. CT and MRI scanners cannot accurately measure very obese people and usually measure smaller body regions. DXA is more accurate than hydrostatic weighing, another commonly used method of determining body fat. Hydrostatic weighing only uses a two-compartment model and is less accurate than DXA. This comparison is also true for DXA versus the Bod Pod, or air displacement plethysmography. A seven-site skinfold measure taken with calipers has a margin of error of about plus or minus 3 percent, according to Georgia State University's department of kinesiology and health. However, if you can find a clinic to perform a DXA scan, you will get a much more accurate measure.

References

Article reviewed by Contributing Writer Last updated on: Mar 28, 2011

Must see: Photo Galleries

Member Comments