Having high levels of body fat can put you at risk for a number of health problems, including diabetes and heart disease. Because of this, many people try to monitor their body fat levels and reduce them or keep them at a healthy level. One tool they use for this is body-fat scales.
How They Work
Scales that measure your body fat use bioelectrical impedance in order to calculate the amount of different types of tissue and water in your body. Basically, an electric current that is too small to be felt is sent through your foot, up your leg, across your hips and back down the other leg, and the amount of time this takes is used to estimate body fat levels. Different proportions of fat and muscle will impede the current to different extents, with fat slowing down the current in comparison to water, which is a major component in muscle and other types of body tissue.
Considerations
A number of different factors can affect the accuracy of bioelectrical impedance in determining body fat percentage, according to a National Institutes of Health assessment of bioelectrical impedance done in 1994. These include the amount of water a person has had to drink, whether or not the person ate or exercised recently, the cleanliness of the feet and body temperature.
Accuracy
Consumer Reports did a comparison in 2003 of the results of DEXA body fat results and the results given by body-fat scales and found that none of the scales were really all that accurate, with some overestimating and some underestimating compared to the laboratory results. However, each scale tends to be consistently inaccurate in the same way, meaning that if it underestimates or overestimates your body fat it will continue to be off in the same way, so it can be used for comparison purposes for those who would like to track changes in their body fat. The scales are less accurate than bioelectrical impedance used in a laboratory setting because they only measure the fat in the lower half of your body, rather than the whole body.
Benefits
Using body-weight scales will allow you to get a better idea of whether or not you have a healthy amount of fat. Although they are not perfectly accurate, they can give a lot of motivation to people who are trying to lose fat because they will be able to track the changes in their body fat.
Expert Insight
Consumer Reports suggests that if you need the motivation of seeing the body fat numbers go down, these scales can provide that. It recommends looking for the scale with the most useful features, including allowing you to save profiles for multiple individuals and guest modes that don't require you to use the memory on the scale.
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