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These Bioelectrical Impedance Analysis (BIA) scales use an imperceptible electrical signal to calculate the amount of water in the body. From this Total Body Water (TBW), it is possible to estimate body fat. This makes these scales quick and easy to use, but there accuracy is limited. The level of hydration has a significant impact on the reading, so readings need to be taken at the same time of day with the same level of hydration. I categorize these scales into three types.
===Lower Body Only===
Most body fat scales have electrodes only on the feet, so the electric current only goes from one foot to the other. This only measures the lower part of the body, not the whole body. Over the years I have found these scales to be near useless; an increase in weight showed was reported disproportionately as fat when other measures show fat levels stayed constant or dropped. I have the Tanita BF680 which retails for [http://www.amazon.com/Tanita-BF680-Scale-Monitor-Athletic/dp/B000094ZGH $60].
http://ecx.images-amazon.com/images/I/41CNM5C5HSL._SS400_.jpg
http://www.tanita.com/data/Image/products/ImageResize/Ironman---BC-558_l.jpg
===Comparison of Lower Body and Full Body Scales===
Over the years I have found lower body scales show that weight loss is disproportionately from non-fat when other measures show fat levels stayed constant or dropped. Here is a recent comparison of weight loss indications from the Tanita and Omron. As you can see, the Omron shows a higher level of fat loss than the Tanita, and I believe that the Omron is more accurate. Notice the large day to day variations; this is why I measure every day and look at the overall average. I use a moving seven day average (the dotted lines) to evaluate the overall progress.
http://fellrnr.com/fellrnr/BFA.JPG
==BOD POD==