Do Body Fat Measurements Tell You What the Scale Can?t?


Q. I just had my body fat measured. Can I trust the number is accurate?

A. Not necessarily. It depends on how it was measured. Accuracy depends on several factors, but the person doing the measuring and the formulas used for calculations are most important.

All methods are really body fat estimations, not measurements. No method is 100% accurate, because none measure body fat directly. Throw in other variables, like an inexperienced technician or eating breakfast beforehand, and a reading can be 3 to 6 percentage points off either way. {Picture 1}

Why measure body fat? It can reveal what scales can’t?how much of your body is fat as opposed to water, bone and muscle. If you have a large muscle mass, you could be overweight but not overfat. Conversely, you could be at your desirable weight but have an unhealthy amount of body fat. Some body fat is essential. of course?more for women than for men. (See chart.) Here’s what you should know about currently popular methods:

Skinfold Calipers. This is the simplest method available, but in practical use is the least accurate. Using calipers, a technician “pinches” skin and the fat beneath it at certain telltale sites (typically triceps, hip and middle thigh). The numbers are then plugged into a formula to estimate body fat. Calipers can be precise, but only in experienced hands. The method can also be inaccurate if your body fat is unevenly distributed (if you have particularly fat arms, for example) or if your flesh is especially flabby or firm.

Approximate Body Fat Standards

InterpretationPercent Body Fat
 MenWomen
Lean<8<15
Optimal Health8-1515-22
Slightly Fat16-2023-26
Fat21-2427-32
Overfat (Obese)>24>32
= greater than
Adapted from Fitness and Sports Medicine, Second Edition, by David Nieman (1990, Mayfield Publishing Company). Reprinted with permission.

Bioelectrical Impedance. This is an increasingly accurate method. It measures body water by sending a weak electrical current through electrodes placed on the ankle and hand. A computer calculates your percent fat based on the amount of water in your body?more water indicates less fat. Readings may be skewed if you are dehydrated (from exercise or alcohol, for example), bloated (especially if premenstrual) or have just eaten (especially a high-carbohydrate meal).

Near-Infrared Resistance. This method?of unknown reliability?is based on the fact that fat and other tissues absorb light differently. A fiberoptic probe shines an infrared light beam onto the biceps. Body fat is calculated by comparing the absorption of two different wavelengths of light.

Underwater Weighing. This is the gold standard, used mostly in research. The person being tested deeply exhales air before being submerged in a tank of water. Body fat is calculated from underwater weight and the displaced water. Air in the lungs or gas in the intestines can distort the numbers, as can improperly calibrated equipment.

EN’s Body Fat Basics:

  • Seek a trained health professional with a background in exercise physiology or nutrition. Avoid fitness expos and health fairs, where unskilled staff may do the measuring.

  • Don’t give a single reading too much credence. Rather. use several readings to monitor change over time.

  • For consistency, use the same method and the same technician each time.

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