How to Measure Body Composition

By: Yuri Elkaim, BPHE, CK, RHN


Obesity is a major problem in our society, being related to hypertension, diabetes, and so much more. In order to deal with this problem we must be able to monitor changes in "body fatness" not just change in weight. After all, weight loss is useless if you lose muscle mass. The goal is to burn fat. But how do we measure that?


Don't Use the BMI

First off, let me warn you about the use of the body mass index (BMI). This is a measure of your weight devided by your height (squared). It is commonly used in medical circles and by pretty much all doctors. However, the problem with the BMI is that it does not detect any change in body fat, only body weight.

Thus, an athlete who may appear to overweight according to the BMI may in fact only have 10% body fat, but you would never know unless you actually measured his body fat using the following methods.


Hydrostatic Underwater Weighing (the gold standard)

Water has a density of about 1 gram/ml, and body fat, with a density of about 0.9 gram/ml, will float in water. Lean (muscle) tissue has a density of about 1.1 gram/ml and will thus sink in water. Therefore, whole body density (using underwater weighing) provides very accurate information about how much of your body is fat and how much is lean tissue. But good luck getting access to this type of measurement. Unless you're at a university, taking part in a scientific study, or are a professional athlete, this type of body fat measure is pretty unrealistic. But there are 2 more that are much more attainable.


Bioelectrial Impedance Analysis (BIA)

The form of body fat testing uses a small portable instrument that your hold with both hands. An electrical (which you don't feel) is then passed through and the resistance to that current (based on the resistance and conductivity of fat-free mass) is then measured. Total body water is calculated and then this value can be used to measure percent body fat. This technique is probably the easiest to use and most accessible. The test takes no more than 10 seconds and its accuracy is pretty good.


Skinfold Thickness

In this test, an estimate of total body fatness is made from a measure of subcutaneous fat. A number of skinfold measurements are taken using skinfold calipers and then these measurements are entered into mathematical equations to calculate body density. This is another accessible technique but it is less reliable because it depends on the accuracy of the measurer selecting the "exact" points to measure skinfold. Also, it can be more invasive than BIA because you are actually grabbing skin and fat in areas that may make you feel uncomfortable.


So there you go. Three of the best ways to measure your body fat. But remember, even if you're working out to lose weight, your goal is really to lose body because you want to preserve your muscle. It is the muscle that, in the long run, will keep you a lean, mean, exercising machine!


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