Q: I am 5 feet 7 1/2 inches tall and weigh 162. My personal trainer measured three sites (once) with calipers and came up with a percentage body fat of 20.2 percent. I do not believe my body fat is that low. How do I know if I am getting an accurate reading? — Claire Meehl, Georgia
A: We have to rely on imperfect tools when measuring our percentage body fat in relation to our lean body mass (muscle, bone, tissue). Any measuring option will give you a general idea of your body composition and, more importantly, how you are progressing. But by and large, these are just approximations.
The four most popular methods for determining body fat percentage are hydrodensitometry weighing (underwater weighing), anthropometry-skinfold (calipers), dual energy X-Ray absorptiometry (DEXA) and bioelectrical impedance.
Underwater weighing is based on the fact that fat floats and lean tissue sinks. If you choose this method, you will be weighed outside the tank, then you will sit in a chair that is attached to a scale. You will then be lowered into a tank of water until you are completely immersed; all air must be exhaled from your lungs. In order to get an accurate measurement, the process is repeated at least three times. A lower immersed weight indicates a higher body fat percentage. The good news with this method is that it is quite accurate; the bad news is the process of being immersed, the highly specialized equipment, and the inaccurate results with athletes and those with osteoporosis. Accuracy in general is within 2 to 3 percent.
A calipers/skinfold measurement can be performed by a fitness trainer, physician or other medical technician. They will measure folds of skin and tissue in three to seven areas where fat normally accumulates (such as the back of the arm, waistline and hip). Sites are usually measured two to three times to check accuracy. The assumption with this method is that the fat under those particular spots is representative of the proportion of body fat found throughout the rest of the body. Pluses are that calipers are easy to use, inexpensive and portable. However, results often depend on the precision and skill of the technician who is doing the measuring. Accuracy is within 2 to 4 percent, again depending on the skill of the technician.
DEXA is a whole-body scanner that is used most frequently to determine bone density. The scan takes about 20 minutes, is non-invasive, safe and very precise. The cost of the equipment is high, which means it will be available primarily in clinical settings. However, the readings are so accurate that the DEXA is surpassing the underwater weigh as the new “gold standard.”
Bioelectrical impedance uses a low-level electrical current that passes through fat, lean mass and water in the body. Each of these conducts the electrical current at a different rate, allowing for a fairly accurate reading of lean mass and fat. It is simple, painless and fast. Accuracy is often compromised with extremely lean or obese people, and the method can be inaccurate if the protocols on eating and drinking before the test are not followed.
Linda J. Buch is a certified fitness trainer in Denver; linda@ljbalance.com.
