A Few More Methods for Measuring Body Fat
In my two previous posts, "Lean-to-Fat Ratio is More Important than BMI" and "How to Measure Your Body Fat," we began a conversation about body composition and body fat.
We addressed the difference between the two, the importance of maintaining a healthy level of body fat, the potential health problems of having too little or too much body fat, and different methods of measuring body fat.
The measuring devices discussed in the previous posts were calipers and bioelectrical impedance monitors. Both are pretty basic and like anything else have good and bad points. There are more measuring techniques and devices and some are high grade.
Anthropometric measurements are measurements of body fat. Different parts of the body are measured including height, weight, and skinfold thickness and the circumference at the waist, hips, and chest. The measurements are then examined and give an accurate assessment of a person's body mass index.
Anthropometric measurements are most commonly used during well-baby checkups but using them with adults can help determine if someone is overweight or underweight.
Hydrostatic weighing or underwater weighing compares a person's weight outside of the water with her weight while submerged in water. Through using the two numbers and the density of the water, a person's density can be accurately measured. That number can then be used to estimate body composition.
Bone and muscle are more dense than water, so a person with a large degree of fat-free mass will weigh more in the water and have a lower percent of body fat. Large amounts of fat mass makes the body lighter when in water and it will have a higher percent of body fat.
Hydrostatic weighing is remarkably accurate and has a low percentage of error. The procedure needs to be administered in a lab setting where subjects must sit completely submerged in water.
Dual-Energy X-Ray Absorptiometry
Dual-Energy X-Ray Absorptiometry or DEXA is becoming the best standard for measuring body fat. It divides the body into total body mineral, fat-free soft mass, and fat tissue mass. Hydrostatic weighing uses only a two compartment model.
DEXA also provides a body fat distribution analysis that can be used to figure out how fat is distributed in different parts of the body. A body scanner is used that administers low-dose x-ray, and the testing takes only 10 to 20 minutes.
The upside to DEXA is the level of accuracy, but it is a pricey procedure.
Air-Displacement Plethysmography requires a subject to sit in a small machine where the amount of air displaced can be used to determine body density. The body density is then used to calculate body composition.
As with hydrostatic weighing and DEXA scans, air-displacement plethysmography may take a bit of effort to access. In addition, the procedure is expensive.
When measuring body fat, it is best to let some time pass between testing. A sufficient period to wait between measurements is about six to eight weeks between measurements