Weight alone is not a reliable tool to determine your fitness. Your weight is the sum total of your fat, muscle, bone and water, and simply relying on a lower number on the scale as a measurement of weight loss leaves out a few variables. Fat loss is what really counts, and the only way to track that is to periodically measure your body fat percentage. There are several different methods with varying degrees of accuracy.
Body Mass Index
The Body Mass Index is the most commonly used method of estimating body fat percentage because it doesn't require any special knowledge or equipment. In fact, many gyms and doctors' offices have charts that allow you to match your height and weight to a specific point to instantly find your estimate. According to the Centers for Disease Control and Prevention, the BMI scale doesn't measure body fat directly, but it correlates to body fat percentages in most people -- people with a high percentage of muscle may obtain a false reading. There are many BMI calculators online, and a normal reading is between 18.5 to 24.9 percent body fat.
Skinfold Calipers
The skinfold method is more accurate than the BMI and is widely used by personal trainers. The trainers use a set of calipers to measure the thickness of a skinfold at three different locations on the body, and then plug the numbers into a formula to determine your body fat percentage. You can buy skinfold calipers to use at home, but the results are more accurate if the measurements are taken by an experienced professional. Taking the measurements in the wrong place or using the calipers incorrectly will skew your results. Acceptable body fat levels using this method range from 14 to 31 percent for women and 6 to 24 percent for men, according to the American Council on Exercise.
Hydrostatic Weighing
Hydrostatic weighing involves sitting on a scale underwater and comparing your buoyancy to your weight. Fat floats -- so the greater the difference is between your dry weight and wet weight, the more fat you likely have. The numbers are run through a series of calculations to determine an exact percentage, and the result is considered more accurate the either the BMI scale or the skinfold method. The problem is that hydrostatic weighing requires a large setup of specialized equipment, as well as trained personnel, so it is only available at sports clinics and other large facilities.
Dual-Energy X-Ray Absorptiometry
Dual-energy X-ray absorptiometry is considered the "gold-standard" when it comes to accuracy in measuring body fat. The test is painless, and the results are considered even more reliable than hydrostatic weighing. The body is scanned with X-ray beams of two different strengths that penetrate to different degrees. The image from each wavelength is then read by the machine, which combines the two images to present a total picture of body composition, including body fat, muscle mass and bone density. Although it's the most reliable method yet found, the procedure requires trained personnel and some very expensive equipment. The procedure is not available in all areas and is generally not covered by insurance.
References
- San Diego State University: Body Composition: Hydrostatic (Underwater) Weighing
- PubMed.gov: Validity of Fan-Beam Dual-Energy X-Ray Absorptiometry for Measuring Fat-Free Mass and Leg Muscle Mass. Health, Aging, and Body Composition Study--Dual-Energy X-Ray Absorptiometry and Body Composition Working Group
- American Council on Exercise: Percent Body Fat Calculator
- Centers for Disease Control and Prevention: About BMI for Adults
- Invision Sally Jobe: DXA Body Composition Analysis (Body Fat Test)
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