Body Fat Testing vs. BMI measurements

I've read a little about BMI and have been concerned a little that people put too much value on their BMI "number". A better method for making informed decisions about the composition of your body is through Body Fat Tests. Here is a good article explaining the differences.

Body Fat Testing Methods

Today when you go after health insurance quotes, it's good to be armed with as much detailed information about your overall physical condition as possible. America is an obese nation, so people with a lower body fat percentage may be able to argue for better premiums or deductibles on their policies. There are several methods for calculating body fat including:

• Hydrodensitometry or Underwater (UWW) Weighing - This underwater method calculates whole body density by measuring volume. The subject sits or lies down on a suspended scale over a pool or tank. The subject is weighed, then submerged and weighed again. Fat is less dense in water, so an individual with greater bone and muscle mass will weigh more when submerged. Using standard formulas, a body density figure is calculated. Although considered the "gold standard" for body fat measurement since the 1940s, many subjects are frightened to be submerged and cannot adequately expel air from their lungs to achieve the most accurate numbers possible. Prices vary widely and tend to be high. Only fitness labs, universities, hospitals, and upper end gyms tend to have access to or actually own the required equipment, which can cost in excess of $50,000.


• Anthropometry (Skinfold Measurement with Calipers) - Hand-held calipers are employed to measure skinfold thickness at 3 to 7 key body locations. A sum of the measurements is then used to calculate a body fat percentage. Since more than 3,500 equations have been validated according to age and ethnic group, this can be an extremely challenging method of calculation. It is, however, easy and inexpensive. Accuracy is, however, questionable with this "old school" methodology in the hands of anyone but a skilled practitioner.


• Absorptiometry (Dual Energy X-Ray or DEXA) - This relatively new and highly sophisticated method used a whole body scanner and low dose x-rays that divide the body into total body mineral, lean, and fat tissue mass. Requiring 10 to 20 minutes, the procedure is non-invasive and comfortable and is rapidly replacing total body immersion or UWW as the "gold standard" body fat measurement due to convenience and price. Depending on location, expect to pay $125 to $250.

Other methods of body fat calculation that are used with less frequency (or exclusively in laboratory settings) include:

• Near Infrared Interactance (NIR)


• Magnetic Resonance Imaging (MRI)


• Total Body Electrical Conductivity (TOBEC)


• Computed Tomography (CT)


• Air Displacement (BOD POD)


• Bioelectrical Impedance (BIA)

In addition to body fat percentage measurements, BMI or Body Mass Index is frequently mentioned in fitness and weight loss literature. BMI is an assessment of weight in relation to height and is often used for the morbidly obese as calipers lose any accuracy with overly large skin folds and UWW tanks may not be large enough or may represent a danger to the subject. BMI does not, however distinguish between fat mass and fat free mass, so no fat percentage calculation is achieved nor is there any accurate sense of where on the body fat is stored, which suggests specific risk factors for various obesity-related disease. Given these limitations, body fat calculations give a much clearer picture of a person’s current physical condition and the goals to which they should aspire.