Weight and body mass index are common ways of determining if you are at a healthy weight. But more than half of the Americans who rate as having a normal body weight actually have too-high body fat percentages, which put them at risk for chronic health problems, reported the Mayo Clinic in 2008. Knowing your body fat helps you to gain a better perspective as to where you fall in terms of a healthy weight range. Measuring body fat can be an expensive and invasive procedure, but home body scales seem to offer a simple and easily accessible alternative.
How Body Fat Scales Work
Scales that measure body fat use bioelectrical impedence analysis. This technique works by transferring a weak electrical current through your body. The scale measures the amount of resistance this current meets along its path. The current passes through muscle much more expediently than it does through fat or bone. The scales really measure your body density and then use a formula to estimate body fat percentage.
Limitations
Because the scales only estimate your body fat, they can be wildly inaccurate. The results can be affected by age, gender, body size and fitness level--some scales ask for information to take these factors into account, some models do not. Consumer Reports tested scales in 2003 and reported their accuracy as "mediocre." They found that even the best scale was only 80 percent accurate. Scales both underestimated and overestimated body fat in the other 20 percent of users, with no clear pattern as to why. When Good Housekeeping tested seven different models, it found that all models overestimated body fat, but offered more accurate results than the caliper method often used in health clubs.
Improving Accuracy
The readings for body fat depend on the temperature of your skin and the room, as well as your hydration levels. To get the most accurate readings, try to measure yourself at the same time every day. Recreate the same hydration level for each test. The website Sports Fitness Advisor suggests drinking the same specific amount of water one hour before you plan to measure yourself. Keep the temperature of the room where the scale is kept consistent. Avoid measuring yourself after intense exercise where you have inevitably sweat out water.
Considerations
If a body fat scale will offer you motivation, it may be worth the investment. You can use the scale, even if it is not completely accurate, to track trends in your body fat over time. It will at least tell you if you are going in the right direction. Scales cost considerably more than your average bathroom model---ranging from $50 to over $100. Consumer Reports suggests looking for a scale that accommodates multiple users so you can have individualized data stored in the scale's memory--increasing the accuracy of your results.
Expert Insight
A study in the Asia-Pacific Journal of Clinical Nutrition in 2008 concluded that a body fat scale offered poor accuracy for individual determination of body composition. The most accurate way to measure body fat is through a DEXA scan--a low-radiation, fully body X-ray--reports CNN. The test is traditionally used to ascertain osteoporosis risk, but does measure fat mass, lean mass and bone mass. The downside is that these tests are not readily available in all clinics and the cost, hundreds of dollars, may be prohibitive.
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